# mapper.py
# Copyright (C) 2005, 2006, 2007, 2008, 2009 Michael Bayer mike_mp@zzzcomputing.com
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""Logic to map Python classes to and from selectables.

Defines the :class:`~sqlalchemy.orm.mapper.Mapper` class, the central configurational
unit which associates a class with a database table.

This is a semi-private module; the main configurational API of the ORM is
available in :class:`~sqlalchemy.orm.`.

"""

import types
import weakref
import operator
from itertools import chain
deque = __import__('collections').deque

from sqlalchemy import sql, util, log, exc as sa_exc
from sqlalchemy.sql import expression, visitors, operators, util as sqlutil
from sqlalchemy.orm import attributes, exc, sync
from sqlalchemy.orm.interfaces import (
    MapperProperty, EXT_CONTINUE, PropComparator
    )
from sqlalchemy.orm.util import (
     ExtensionCarrier, _INSTRUMENTOR, _class_to_mapper, _state_has_identity,
     _state_mapper, class_mapper, instance_str, state_str,
     )

__all__ = (
    'Mapper',
    '_mapper_registry',
    'class_mapper',
    'object_mapper',
    )

_mapper_registry = weakref.WeakKeyDictionary()
_new_mappers = False
_already_compiling = False

# a list of MapperExtensions that will be installed in all mappers by default
global_extensions = []

# a constant returned by _get_attr_by_column to indicate
# this mapper is not handling an attribute for a particular
# column
NO_ATTRIBUTE = util.symbol('NO_ATTRIBUTE')

# lock used to synchronize the "mapper compile" step
_COMPILE_MUTEX = util.threading.RLock()

# initialize these lazily
ColumnProperty = None
SynonymProperty = None
ComparableProperty = None
RelationProperty = None
ConcreteInheritedProperty = None
_expire_state = None
_state_session = None

class Mapper(object):
    """Define the correlation of class attributes to database table
    columns.

    Instances of this class should be constructed via the
    :func:`~sqlalchemy.orm.mapper` function.

    """
    def __init__(self,
                 class_,
                 local_table,
                 properties = None,
                 primary_key = None,
                 non_primary = False,
                 inherits = None,
                 inherit_condition = None,
                 inherit_foreign_keys = None,
                 extension = None,
                 order_by = False,
                 always_refresh = False,
                 version_id_col = None,
                 polymorphic_on=None,
                 _polymorphic_map=None,
                 polymorphic_identity=None,
                 polymorphic_fetch=None,
                 concrete=False,
                 select_table=None,
                 with_polymorphic=None,
                 allow_null_pks=False,
                 batch=True,
                 column_prefix=None,
                 include_properties=None,
                 exclude_properties=None,
                 eager_defaults=False):
        """Construct a new mapper.

        Mappers are normally constructed via the :func:`~sqlalchemy.orm.mapper`
        function.  See for details.

        """

        self.class_ = util.assert_arg_type(class_, type, 'class_')

        self.class_manager = None

        self.primary_key_argument = primary_key
        self.non_primary = non_primary

        if order_by:
            self.order_by = util.to_list(order_by)
        else:
            self.order_by = order_by
        
        self.always_refresh = always_refresh
        self.version_id_col = version_id_col
        self.concrete = concrete
        self.single = False
        self.inherits = inherits
        self.local_table = local_table
        self.inherit_condition = inherit_condition
        self.inherit_foreign_keys = inherit_foreign_keys
        self.extension = extension
        self._init_properties = properties or {}
        self.allow_null_pks = allow_null_pks
        self.delete_orphans = []
        self.batch = batch
        self.eager_defaults = eager_defaults
        self.column_prefix = column_prefix
        self.polymorphic_on = polymorphic_on
        self._dependency_processors = []
        self._validators = {}
        self._clause_adapter = None
        self._requires_row_aliasing = False
        self._inherits_equated_pairs = None


        self.select_table = select_table
        if select_table:
            util.warn_deprecated('select_table option is deprecated.  Use with_polymorphic=("*", selectable) '
                            'instead.')

            if with_polymorphic:
                raise sa_exc.ArgumentError("select_table can't be used with "
                            "with_polymorphic (they define conflicting settings)")
            self.with_polymorphic = ('*', select_table)
        else:
            if with_polymorphic == '*':
                self.with_polymorphic = ('*', None)
            elif isinstance(with_polymorphic, (tuple, list)):
                if isinstance(with_polymorphic[0], (basestring, tuple, list)):
                    self.with_polymorphic = with_polymorphic
                else:
                    self.with_polymorphic = (with_polymorphic, None)
            elif with_polymorphic is not None:
                raise sa_exc.ArgumentError("Invalid setting for with_polymorphic")
            else:
                self.with_polymorphic = None

        if isinstance(self.local_table, expression._SelectBaseMixin):
            util.warn("mapper %s creating an alias for the given "
                        "selectable.  References to the original selectable "
                        "may be misinterpreted by queries, polymorphic_on, etc. "
                        " Consider passing an explicit selectable.alias() construct instead." % self)
            self.local_table = self.local_table.alias()

        if self.with_polymorphic and isinstance(self.with_polymorphic[1], expression._SelectBaseMixin):
            self.with_polymorphic = (self.with_polymorphic[0], self.with_polymorphic[1].alias())

        # our 'polymorphic identity', a string name that when located in a result set row
        # indicates this Mapper should be used to construct the object instance for that row.
        self.polymorphic_identity = polymorphic_identity

        if polymorphic_fetch:
            util.warn_deprecated('polymorphic_fetch option is deprecated.  Unloaded columns '
                            'load as deferred in all cases; loading can be controlled '
                            'using the "with_polymorphic" option.')

        # a dictionary of 'polymorphic identity' names, associating those names with
        # Mappers that will be used to construct object instances upon a select operation.
        if _polymorphic_map is None:
            self.polymorphic_map = {}
        else:
            self.polymorphic_map = _polymorphic_map

        self.include_properties = include_properties
        self.exclude_properties = exclude_properties

        self.compiled = False

        self._configure_inheritance()
        self._configure_extensions()
        self._configure_class_instrumentation()
        self._configure_properties()
        self._configure_pks()
        global _new_mappers
        _new_mappers = True
        self._log("constructed")

    # configurational / mutating methods.  not threadsafe
    # except for compile().
    
    def _configure_inheritance(self):
        """Configure settings related to inherting and/or inherited mappers being present."""

        # a set of all mappers which inherit from this one.
        self._inheriting_mappers = set()

        if self.inherits:
            if isinstance(self.inherits, type):
                self.inherits = class_mapper(self.inherits, compile=False)
            if not issubclass(self.class_, self.inherits.class_):
                raise sa_exc.ArgumentError(
                        "Class '%s' does not inherit from '%s'" % 
                        (self.class_.__name__, self.inherits.class_.__name__))
            if self.non_primary != self.inherits.non_primary:
                np = not self.non_primary and "primary" or "non-primary"
                raise sa_exc.ArgumentError("Inheritance of %s mapper for class '%s' is "
                        "only allowed from a %s mapper" % (np, self.class_.__name__, np))
            # inherit_condition is optional.
            if self.local_table is None:
                self.local_table = self.inherits.local_table
                self.mapped_table = self.inherits.mapped_table
                self.single = True
            elif not self.local_table is self.inherits.local_table:
                if self.concrete:
                    self.mapped_table = self.local_table
                    for mapper in self.iterate_to_root():
                        if mapper.polymorphic_on:
                            mapper._requires_row_aliasing = True
                else:
                    if not self.inherit_condition:
                        # figure out inherit condition from our table to the immediate table
                        # of the inherited mapper, not its full table which could pull in other
                        # stuff we dont want (allows test/inheritance.InheritTest4 to pass)
                        self.inherit_condition = sqlutil.join_condition(self.inherits.local_table, self.local_table)
                    self.mapped_table = sql.join(self.inherits.mapped_table, self.local_table, self.inherit_condition)

                    fks = util.to_set(self.inherit_foreign_keys)
                    self._inherits_equated_pairs = sqlutil.criterion_as_pairs(self.mapped_table.onclause, consider_as_foreign_keys=fks)
            else:
                self.mapped_table = self.local_table

            if self.polymorphic_identity and not self.concrete:
                self._identity_class = self.inherits._identity_class
            else:
                self._identity_class = self.class_

            if self.version_id_col is None:
                self.version_id_col = self.inherits.version_id_col

            for mapper in self.iterate_to_root():
                util.reset_memoized(mapper, '_equivalent_columns')
                util.reset_memoized(mapper, '_sorted_tables')
                
            if self.order_by is False and not self.concrete and self.inherits.order_by is not False:
                self.order_by = self.inherits.order_by

            self.polymorphic_map = self.inherits.polymorphic_map
            self.batch = self.inherits.batch
            self.inherits._inheriting_mappers.add(self)
            self.base_mapper = self.inherits.base_mapper
            self._all_tables = self.inherits._all_tables

            if self.polymorphic_identity is not None:
                self.polymorphic_map[self.polymorphic_identity] = self
                if not self.polymorphic_on:
                    for mapper in self.iterate_to_root():
                        # try to set up polymorphic on using correesponding_column(); else leave
                        # as None
                        if mapper.polymorphic_on:
                            self.polymorphic_on = self.mapped_table.corresponding_column(mapper.polymorphic_on)
                            break
        else:
            self._all_tables = set()
            self.base_mapper = self
            self.mapped_table = self.local_table
            if self.polymorphic_identity:
                self.polymorphic_map[self.polymorphic_identity] = self
            self._identity_class = self.class_

        if self.mapped_table is None:
            raise sa_exc.ArgumentError("Mapper '%s' does not have a mapped_table specified." % self)

    def _configure_extensions(self):
        """Go through the global_extensions list as well as the list
        of ``MapperExtensions`` specified for this ``Mapper`` and
        creates a linked list of those extensions.
        
        """
        extlist = util.OrderedSet()

        extension = self.extension
        if extension:
            for ext_obj in util.to_list(extension):
                # local MapperExtensions have already instrumented the class
                extlist.add(ext_obj)

        if self.inherits:
            for ext in self.inherits.extension:
                if ext not in extlist:
                    extlist.add(ext)
        else:
            for ext in global_extensions:
                if isinstance(ext, type):
                    ext = ext()
                if ext not in extlist:
                    extlist.add(ext)

        self.extension = ExtensionCarrier()
        for ext in extlist:
            self.extension.append(ext)

    def _configure_class_instrumentation(self):
        """If this mapper is to be a primary mapper (i.e. the
        non_primary flag is not set), associate this Mapper with the
        given class_ and entity name.

        Subsequent calls to ``class_mapper()`` for the class_/entity
        name combination will return this mapper.  Also decorate the
        `__init__` method on the mapped class to include optional
        auto-session attachment logic.

        """
        manager = attributes.manager_of_class(self.class_)

        if self.non_primary:
            if not manager or manager.mapper is None:
                raise sa_exc.InvalidRequestError(
                    "Class %s has no primary mapper configured.  Configure "
                    "a primary mapper first before setting up a non primary "
                    "Mapper.")
            self.class_manager = manager
            _mapper_registry[self] = True
            return

        if manager is not None:
            assert manager.class_ is self.class_
            if manager.mapper:
                raise sa_exc.ArgumentError(
                    "Class '%s' already has a primary mapper defined. "
                    "Use non_primary=True to "
                    "create a non primary Mapper.  clear_mappers() will "
                    "remove *all* current mappers from all classes." %
                    self.class_)
            #else:
                # a ClassManager may already exist as 
                # ClassManager.instrument_attribute() creates 
                # new managers for each subclass if they don't yet exist.
                
        _mapper_registry[self] = True

        self.extension.instrument_class(self, self.class_)

        if manager is None:
            manager = attributes.register_class(self.class_, 
                deferred_scalar_loader = _load_scalar_attributes
            )

        self.class_manager = manager

        manager.mapper = self

        # The remaining members can be added by any mapper, e_name None or not.
        if manager.info.get(_INSTRUMENTOR, False):
            return

        event_registry = manager.events
        event_registry.add_listener('on_init', _event_on_init)
        event_registry.add_listener('on_init_failure', _event_on_init_failure)
        event_registry.add_listener('on_resurrect', _event_on_resurrect)
        
        for key, method in util.iterate_attributes(self.class_):
            if isinstance(method, types.FunctionType):
                if hasattr(method, '__sa_reconstructor__'):
                    event_registry.add_listener('on_load', method)
                elif hasattr(method, '__sa_validators__'):
                    for name in method.__sa_validators__:
                        self._validators[name] = method

        if 'reconstruct_instance' in self.extension:
            def reconstruct(instance):
                self.extension.reconstruct_instance(self, instance)
            event_registry.add_listener('on_load', reconstruct)

        manager.info[_INSTRUMENTOR] = self

    def dispose(self):
        # Disable any attribute-based compilation.
        self.compiled = True
        
        if hasattr(self, '_compile_failed'):
            del self._compile_failed
            
        if not self.non_primary and self.class_manager.mapper is self:
            attributes.unregister_class(self.class_)

    def _configure_pks(self):

        self.tables = sqlutil.find_tables(self.mapped_table)

        if not self.tables:
            raise sa_exc.InvalidRequestError("Could not find any Table objects in mapped table '%s'" % str(self.mapped_table))

        self._pks_by_table = {}
        self._cols_by_table = {}

        all_cols = util.column_set(chain(*[col.proxy_set for col in self._columntoproperty]))
        pk_cols = util.column_set(c for c in all_cols if c.primary_key)

        # identify primary key columns which are also mapped by this mapper.
        tables = set(self.tables + [self.mapped_table])
        self._all_tables.update(tables)
        for t in tables:
            if t.primary_key and pk_cols.issuperset(t.primary_key):
                # ordering is important since it determines the ordering of mapper.primary_key (and therefore query.get())
                self._pks_by_table[t] = util.ordered_column_set(t.primary_key).intersection(pk_cols)
            self._cols_by_table[t] = util.ordered_column_set(t.c).intersection(all_cols)

        # determine cols that aren't expressed within our tables; mark these
        # as "read only" properties which are refreshed upon INSERT/UPDATE
        self._readonly_props = set(
            self._columntoproperty[col]
            for col in self._columntoproperty
            if not hasattr(col, 'table') or col.table not in self._cols_by_table)

        # if explicit PK argument sent, add those columns to the primary key mappings
        if self.primary_key_argument:
            for k in self.primary_key_argument:
                if k.table not in self._pks_by_table:
                    self._pks_by_table[k.table] = util.OrderedSet()
                self._pks_by_table[k.table].add(k)

        if self.mapped_table not in self._pks_by_table or len(self._pks_by_table[self.mapped_table]) == 0:
            raise sa_exc.ArgumentError("Mapper %s could not assemble any primary "
                    "key columns for mapped table '%s'" % (self, self.mapped_table.description))

        if self.inherits and not self.concrete and not self.primary_key_argument:
            # if inheriting, the "primary key" for this mapper is that of the inheriting (unless concrete or explicit)
            self.primary_key = self.inherits.primary_key
        else:
            # determine primary key from argument or mapped_table pks - reduce to the minimal set of columns
            if self.primary_key_argument:
                primary_key = sqlutil.reduce_columns(
                    [self.mapped_table.corresponding_column(c) for c in self.primary_key_argument],
                    ignore_nonexistent_tables=True)
            else:
                primary_key = sqlutil.reduce_columns(
                    self._pks_by_table[self.mapped_table], ignore_nonexistent_tables=True)

            if len(primary_key) == 0:
                raise sa_exc.ArgumentError("Mapper %s could not assemble any primary "
                    "key columns for mapped table '%s'" % (self, self.mapped_table.description))

            self.primary_key = primary_key
            self._log("Identified primary key columns: " + str(primary_key))

    def _configure_properties(self):
        
        # Column and other ClauseElement objects which are mapped
        self.columns = self.c = util.OrderedProperties()

        # object attribute names mapped to MapperProperty objects
        self._props = util.OrderedDict()

        # table columns mapped to lists of MapperProperty objects
        # using a list allows a single column to be defined as
        # populating multiple object attributes
        self._columntoproperty = util.column_dict()

        # load custom properties
        if self._init_properties:
            for key, prop in self._init_properties.iteritems():
                self._configure_property(key, prop, False)

        # pull properties from the inherited mapper if any.
        if self.inherits:
            for key, prop in self.inherits._props.iteritems():
                if key not in self._props and not self._should_exclude(key, key, local=False):
                    self._adapt_inherited_property(key, prop, False)

        # create properties for each column in the mapped table,
        # for those columns which don't already map to a property
        for column in self.mapped_table.columns:
            if column in self._columntoproperty:
                continue

            column_key = (self.column_prefix or '') + column.key

            if self._should_exclude(column.key, column_key, local=self.local_table.c.contains_column(column)):
                continue

            # adjust the "key" used for this column to that
            # of the inheriting mapper
            for mapper in self.iterate_to_root():
                if column in mapper._columntoproperty:
                    column_key = mapper._columntoproperty[column].key

            self._configure_property(column_key, column, init=False, setparent=True)

        # do a special check for the "discriminiator" column, as it may only be present
        # in the 'with_polymorphic' selectable but we need it for the base mapper
        if self.polymorphic_on and self.polymorphic_on not in self._columntoproperty:
            col = self.mapped_table.corresponding_column(self.polymorphic_on)
            if not col:
                dont_instrument = True
                col = self.polymorphic_on
            else:
                dont_instrument = False
            if self._should_exclude(col.key, col.key, local=False):
                raise sa_exc.InvalidRequestError("Cannot exclude or override the discriminator column %r" % col.key)
            self._configure_property(col.key, ColumnProperty(col, _no_instrument=dont_instrument), init=False, setparent=True)

    def _adapt_inherited_property(self, key, prop, init):
        if not self.concrete:
            self._configure_property(key, prop, init=False, setparent=False)
        elif key not in self._props:
            self._configure_property(key, ConcreteInheritedProperty(), init=init, setparent=True)
            
    def _configure_property(self, key, prop, init=True, setparent=True):
        self._log("_configure_property(%s, %s)" % (key, prop.__class__.__name__))

        if not isinstance(prop, MapperProperty):
            # we were passed a Column or a list of Columns; generate a ColumnProperty
            columns = util.to_list(prop)
            column = columns[0]
            if not expression.is_column(column):
                raise sa_exc.ArgumentError("%s=%r is not an instance of MapperProperty or Column" % (key, prop))

            prop = self._props.get(key, None)

            if isinstance(prop, ColumnProperty):
                # TODO: the "property already exists" case is still not well defined here.
                # assuming single-column, etc.

                if prop.parent is not self:
                    # existing ColumnProperty from an inheriting mapper.
                    # make a copy and append our column to it
                    prop = prop.copy()
                prop.columns.append(column)
                self._log("appending to existing ColumnProperty %s" % (key))
            elif prop is None or isinstance(prop, ConcreteInheritedProperty):
                mapped_column = []
                for c in columns:
                    mc = self.mapped_table.corresponding_column(c)
                    if not mc:
                        raise sa_exc.ArgumentError("Column '%s' is not represented in mapper's table.  "
                            "Use the `column_property()` function to force this column "
                            "to be mapped as a read-only attribute." % c)
                    mapped_column.append(mc)
                prop = ColumnProperty(*mapped_column)
            else:
                raise sa_exc.ArgumentError("WARNING: column '%s' conflicts with property '%r'.  "
                    "To resolve this, map the column to the class under a different "
                    "name in the 'properties' dictionary.  Or, to remove all awareness "
                    "of the column entirely (including its availability as a foreign key), "
                    "use the 'include_properties' or 'exclude_properties' mapper arguments "
                    "to control specifically which table columns get mapped." % (column.key, prop))

        if isinstance(prop, ColumnProperty):
            col = self.mapped_table.corresponding_column(prop.columns[0])
            # col might not be present! the selectable given to the mapper need not include "deferred"
            # columns (included in zblog tests)
            if col is None:
                col = prop.columns[0]

                # column is coming in after _readonly_props was initialized; check
                # for 'readonly'
                if hasattr(self, '_readonly_props') and \
                    (not hasattr(col, 'table') or col.table not in self._cols_by_table):
                        self._readonly_props.add(prop)

            else:
                # if column is coming in after _cols_by_table was initialized, ensure the col is in the
                # right set
                if hasattr(self, '_cols_by_table') and col.table in self._cols_by_table and col not in self._cols_by_table[col.table]:
                    self._cols_by_table[col.table].add(col)
            
            # if this ColumnProperty represents the "polymorphic discriminator"
            # column, mark it.  We'll need this when rendering columns
            # in SELECT statements.
            if not hasattr(prop, '_is_polymorphic_discriminator'):
                prop._is_polymorphic_discriminator = (col is self.polymorphic_on or prop.columns[0] is self.polymorphic_on)
                
            self.columns[key] = col
            for col in prop.columns:
                for col in col.proxy_set:
                    self._columntoproperty[col] = prop

        elif isinstance(prop, (ComparableProperty, SynonymProperty)) and setparent:
            if prop.descriptor is None:
                desc = getattr(self.class_, key, None)
                if self._is_userland_descriptor(desc):
                    prop.descriptor = desc
            if getattr(prop, 'map_column', False):
                if key not in self.mapped_table.c:
                    raise sa_exc.ArgumentError(
                        "Can't compile synonym '%s': no column on table '%s' named '%s'" 
                         % (prop.name, self.mapped_table.description, key))
                self._configure_property(prop.name, ColumnProperty(self.mapped_table.c[key]), init=init, setparent=setparent)

        self._props[key] = prop
        prop.key = key

        if setparent:
            prop.set_parent(self)

        if not self.non_primary:
            prop.instrument_class(self)

        for mapper in self._inheriting_mappers:
            mapper._adapt_inherited_property(key, prop, init)

        if init:
            prop.init()
            prop.post_instrument_class(self)


    def compile(self):
        """Compile this mapper and all other non-compiled mappers.

        This method checks the local compiled status as well as for
        any new mappers that have been defined, and is safe to call
        repeatedly.

        """
        global _new_mappers
        if self.compiled and not _new_mappers:
            return self

        _COMPILE_MUTEX.acquire()
        try:
            try:
                global _already_compiling
                if _already_compiling:
                    # re-entrance to compile() occurs rarely, when a class-mapped construct is
                    # used within a ForeignKey, something that is possible
                    # when using the declarative layer
                    self._post_configure_properties()
                    return
                _already_compiling = True
                try:

                    # double-check inside mutex
                    if self.compiled and not _new_mappers:
                        return self

                    # initialize properties on all mappers
                    for mapper in list(_mapper_registry):
                        if getattr(mapper, '_compile_failed', False):
                            raise sa_exc.InvalidRequestError("One or more mappers failed to compile.  Exception was probably "
                                    "suppressed within a hasattr() call. "
                                    "Message was: %s" % mapper._compile_failed)
                        if not mapper.compiled:
                            mapper._post_configure_properties()

                    _new_mappers = False
                    return self
                finally:
                    _already_compiling = False
            except:
                import sys
                exc = sys.exc_info()[1]
                self._compile_failed = exc
                raise
        finally:
            _COMPILE_MUTEX.release()

    def _post_configure_properties(self):
        """Call the ``init()`` method on all ``MapperProperties``
        attached to this mapper.

        This is a deferred configuration step which is intended
        to execute once all mappers have been constructed.
        
        """

        self._log("_post_configure_properties() started")
        l = [(key, prop) for key, prop in self._props.iteritems()]
        for key, prop in l:
            self._log("initialize prop " + key)
            
            if prop.parent is self and not prop._compile_started:
                prop.init()
            
            if prop._compile_finished:
                prop.post_instrument_class(self)
            
        self._log("_post_configure_properties() complete")
        self.compiled = True
            
    def add_properties(self, dict_of_properties):
        """Add the given dictionary of properties to this mapper,
        using `add_property`.

        """
        for key, value in dict_of_properties.iteritems():
            self.add_property(key, value)

    def add_property(self, key, prop):
        """Add an individual MapperProperty to this mapper.

        If the mapper has not been compiled yet, just adds the
        property to the initial properties dictionary sent to the
        constructor.  If this Mapper has already been compiled, then
        the given MapperProperty is compiled immediately.

        """
        self._init_properties[key] = prop
        self._configure_property(key, prop, init=self.compiled)


    # class formatting / logging.
    
    def _log(self, msg):
        if self._should_log_info:
            self.logger.info(
                "(" + self.class_.__name__ + 
                "|" + 
                (self.local_table and self.local_table.description or str(self.local_table)) +
                (self.non_primary and "|non-primary" or "") + ") " + 
                msg)

    def _log_debug(self, msg):
        if self._should_log_debug:
            self.logger.debug(
                "(" + self.class_.__name__ + 
                "|" + 
                (self.local_table and self.local_table.description or str(self.local_table)) + 
                (self.non_primary and "|non-primary" or "") + ") " + 
                msg)

    def __repr__(self):
        return '<Mapper at 0x%x; %s>' % (
            id(self), self.class_.__name__)

    def __str__(self):
        return "Mapper|" + self.class_.__name__ + "|" + \
                (self.local_table and self.local_table.description or str(self.local_table)) + \
                (self.non_primary and "|non-primary" or "")

    # informational / status
    
    def _is_orphan(self, state):
        o = False
        for mapper in self.iterate_to_root():
            for (key, cls) in mapper.delete_orphans:
                if attributes.manager_of_class(cls).has_parent(
                    state, key, optimistic=_state_has_identity(state)):
                    return False
            o = o or bool(mapper.delete_orphans)
        return o

    def has_property(self, key):
        return key in self._props

    def get_property(self, key, resolve_synonyms=False, raiseerr=True):
        """return a MapperProperty associated with the given key."""

        self.compile()
        return self._get_property(key, resolve_synonyms=resolve_synonyms, raiseerr=raiseerr)

    def _get_property(self, key, resolve_synonyms=False, raiseerr=True):
        prop = self._props.get(key, None)
        if resolve_synonyms:
            while isinstance(prop, SynonymProperty):
                prop = self._props.get(prop.name, None)
        if prop is None and raiseerr:
            raise sa_exc.InvalidRequestError("Mapper '%s' has no property '%s'" % (str(self), key))
        return prop
    
    @property
    def iterate_properties(self):
        """return an iterator of all MapperProperty objects."""
        self.compile()
        return self._props.itervalues()

    def _mappers_from_spec(self, spec, selectable):
        """given a with_polymorphic() argument, return the set of mappers it represents.

        Trims the list of mappers to just those represented within the given selectable, if present.
        This helps some more legacy-ish mappings.

        """
        if spec == '*':
            mappers = list(self.polymorphic_iterator())
        elif spec:
            mappers = [_class_to_mapper(m) for m in util.to_list(spec)]
            for m in mappers:
                if not m.isa(self):
                    raise sa_exc.InvalidRequestError("%r does not inherit from %r"  % (m, self))
        else:
            mappers = []

        if selectable:
            tables = set(sqlutil.find_tables(selectable, include_aliases=True))
            mappers = [m for m in mappers if m.local_table in tables]

        return mappers

    def _selectable_from_mappers(self, mappers):
        """given a list of mappers (assumed to be within this mapper's inheritance hierarchy),
        construct an outerjoin amongst those mapper's mapped tables.

        """
        
        from_obj = self.mapped_table
        for m in mappers:
            if m is self:
                continue
            if m.concrete:
                raise sa_exc.InvalidRequestError("'with_polymorphic()' requires 'selectable' argument when concrete-inheriting mappers are used.")
            elif not m.single:
                from_obj = from_obj.outerjoin(m.local_table, m.inherit_condition)

        return from_obj

    @property
    def _single_table_criterion(self):
        if self.single and \
            self.inherits and \
            self.polymorphic_on and \
            self.polymorphic_identity is not None:
            return self.polymorphic_on.in_(
                m.polymorphic_identity
                for m in self.polymorphic_iterator())
        else:
            return None
        
    
    @util.memoized_property
    def _with_polymorphic_mappers(self):
        if not self.with_polymorphic:
            return [self]
        return self._mappers_from_spec(*self.with_polymorphic)

    @util.memoized_property
    def _with_polymorphic_selectable(self):
        if not self.with_polymorphic:
            return self.mapped_table

        spec, selectable = self.with_polymorphic
        if selectable:
            return selectable
        else:
            return self._selectable_from_mappers(self._mappers_from_spec(spec, selectable))

    def _with_polymorphic_args(self, spec=None, selectable=False):
        if self.with_polymorphic:
            if not spec:
                spec = self.with_polymorphic[0]
            if selectable is False:
                selectable = self.with_polymorphic[1]

        mappers = self._mappers_from_spec(spec, selectable)
        if selectable:
            return mappers, selectable
        else:
            return mappers, self._selectable_from_mappers(mappers)

    def _iterate_polymorphic_properties(self, mappers=None):
        """Return an iterator of MapperProperty objects which will render into a SELECT."""
        
        if mappers is None:
            mappers = self._with_polymorphic_mappers

        if not mappers:
            for c in self.iterate_properties:
                yield c
        else:
            # in the polymorphic case, filter out discriminator columns
            # from other mappers, as these are sometimes dependent on that
            # mapper's polymorphic selectable (which we don't want rendered)
            for c in util.unique_list(
                chain(*[list(mapper.iterate_properties) for mapper in [self] + mappers])
            ):
                if getattr(c, '_is_polymorphic_discriminator', False) and \
                    (not self.polymorphic_on or c.columns[0] is not self.polymorphic_on):
                        continue
                yield c
    
    @property
    def properties(self):
        raise NotImplementedError("Public collection of MapperProperty objects is "
                    "provided by the get_property() and iterate_properties accessors.")

    @util.memoized_property
    def _get_clause(self):
        """create a "get clause" based on the primary key.  this is used
        by query.get() and many-to-one lazyloads to load this item
        by primary key.

        """
        params = [(primary_key, sql.bindparam(None, type_=primary_key.type)) for primary_key in self.primary_key]
        return sql.and_(*[k==v for (k, v) in params]), util.column_dict(params)

    @util.memoized_property
    def _equivalent_columns(self):
        """Create a map of all *equivalent* columns, based on
        the determination of column pairs that are equated to
        one another based on inherit condition.  This is designed
        to work with the queries that util.polymorphic_union
        comes up with, which often don't include the columns from
        the base table directly (including the subclass table columns
        only).

        The resulting structure is a dictionary of columns mapped
        to lists of equivalent columns, i.e.

        {
            tablea.col1:
                set([tableb.col1, tablec.col1]),
            tablea.col2:
                set([tabled.col2])
        }

        """
        result = util.column_dict()
        def visit_binary(binary):
            if binary.operator == operators.eq:
                if binary.left in result:
                    result[binary.left].add(binary.right)
                else:
                    result[binary.left] = util.column_set((binary.right,))
                if binary.right in result:
                    result[binary.right].add(binary.left)
                else:
                    result[binary.right] = util.column_set((binary.left,))
        for mapper in self.base_mapper.polymorphic_iterator():
            if mapper.inherit_condition:
                visitors.traverse(mapper.inherit_condition, {}, {'binary':visit_binary})

        return result

    def _is_userland_descriptor(self, obj):
        return not isinstance(obj, (MapperProperty, attributes.InstrumentedAttribute)) and hasattr(obj, '__get__')

    def _should_exclude(self, name, assigned_name, local):
        """determine whether a particular property should be implicitly present on the class.

        This occurs when properties are propagated from an inherited class, or are
        applied from the columns present in the mapped table.

        """

        # check for descriptors, either local or from
        # an inherited class
        if local:
            if self.class_.__dict__.get(assigned_name, None)\
                and self._is_userland_descriptor(self.class_.__dict__[assigned_name]):
                return True
        else:
            if getattr(self.class_, assigned_name, None)\
                and self._is_userland_descriptor(getattr(self.class_, assigned_name)):
                return True

        if (self.include_properties is not None and
            name not in self.include_properties):
            self._log("not including property %s" % (name))
            return True

        if (self.exclude_properties is not None and
            name in self.exclude_properties):
            self._log("excluding property %s" % (name))
            return True

        return False

    def common_parent(self, other):
        """Return true if the given mapper shares a common inherited parent as this mapper."""

        return self.base_mapper is other.base_mapper

    def _canload(self, state, allow_subtypes):
        s = self.primary_mapper()
        if self.polymorphic_on or allow_subtypes:
            return _state_mapper(state).isa(s)
        else:
            return _state_mapper(state) is s

    def isa(self, other):
        """Return True if the this mapper inherits from the given mapper."""

        m = self
        while m and m is not other:
            m = m.inherits
        return bool(m)

    def iterate_to_root(self):
        m = self
        while m:
            yield m
            m = m.inherits

    def polymorphic_iterator(self):
        """Iterate through the collection including this mapper and
        all descendant mappers.

        This includes not just the immediately inheriting mappers but
        all their inheriting mappers as well.

        To iterate through an entire hierarchy, use
        ``mapper.base_mapper.polymorphic_iterator()``.
        
        """
        stack = deque([self])
        while stack:
            item = stack.popleft()
            yield item
            stack.extend(item._inheriting_mappers)

    def primary_mapper(self):
        """Return the primary mapper corresponding to this mapper's class key (class)."""
        
        return self.class_manager.mapper

    def identity_key_from_row(self, row, adapter=None):
        """Return an identity-map key for use in storing/retrieving an
        item from the identity map.

        row
          A ``sqlalchemy.engine.base.RowProxy`` instance or a
          dictionary corresponding result-set ``ColumnElement``
          instances to their values within a row.

        """
        pk_cols = self.primary_key
        if adapter:
            pk_cols = [adapter.columns[c] for c in pk_cols]

        return (self._identity_class, tuple(row[column] for column in pk_cols))

    def identity_key_from_primary_key(self, primary_key):
        """Return an identity-map key for use in storing/retrieving an
        item from an identity map.

        primary_key
          A list of values indicating the identifier.

        """
        return (self._identity_class, tuple(util.to_list(primary_key)))

    def identity_key_from_instance(self, instance):
        """Return the identity key for the given instance, based on
        its primary key attributes.

        This value is typically also found on the instance state under the
        attribute name `key`.

        """
        return self.identity_key_from_primary_key(self.primary_key_from_instance(instance))

    def _identity_key_from_state(self, state):
        return self.identity_key_from_primary_key(self._primary_key_from_state(state))

    def primary_key_from_instance(self, instance):
        """Return the list of primary key values for the given
        instance.

        """
        state = attributes.instance_state(instance)
        return self._primary_key_from_state(state)

    def _primary_key_from_state(self, state):
        return [self._get_state_attr_by_column(state, column) for column in self.primary_key]

    def _get_col_to_prop(self, column):
        try:
            return self._columntoproperty[column]
        except KeyError:
            prop = self._props.get(column.key, None)
            if prop:
                raise exc.UnmappedColumnError("Column '%s.%s' is not available, due to conflicting property '%s':%s" % (column.table.name, column.name, column.key, repr(prop)))
            else:
                raise exc.UnmappedColumnError("No column %s is configured on mapper %s..." % (column, self))

    # TODO: improve names?
    def _get_state_attr_by_column(self, state, column):
        return self._get_col_to_prop(column).getattr(state, column)

    def _set_state_attr_by_column(self, state, column, value):
        return self._get_col_to_prop(column).setattr(state, value, column)

    def _get_committed_attr_by_column(self, obj, column):
        state = attributes.instance_state(obj)
        return self._get_committed_state_attr_by_column(state, column)

    def _get_committed_state_attr_by_column(self, state, column, passive=False):
        return self._get_col_to_prop(column).getcommitted(state, column, passive=passive)

    def _optimized_get_statement(self, state, attribute_names):
        """assemble a WHERE clause which retrieves a given state by primary key, using a minimized set of tables.
        
        Applies to a joined-table inheritance mapper where the 
        requested attribute names are only present on joined tables,
        not the base table.  The WHERE clause attempts to include 
        only those tables to minimize joins.
        
        """
        props = self._props
        tables = set(props[key].parent.local_table for key in attribute_names)
        if self.base_mapper.local_table in tables:
            return None

        class ColumnsNotAvailable(Exception):
            pass

        def visit_binary(binary):
            leftcol = binary.left
            rightcol = binary.right
            if leftcol is None or rightcol is None:
                return

            if leftcol.table not in tables:
                leftval = self._get_committed_state_attr_by_column(state, leftcol, passive=True)
                if leftval is attributes.PASSIVE_NORESULT:
                    raise ColumnsNotAvailable()
                binary.left = sql.bindparam(None, leftval, type_=binary.right.type)
            elif rightcol.table not in tables:
                rightval = self._get_committed_state_attr_by_column(state, rightcol, passive=True)
                if rightval is attributes.PASSIVE_NORESULT:
                    raise ColumnsNotAvailable()
                binary.right = sql.bindparam(None, rightval, type_=binary.right.type)

        allconds = []

        try:
            start = False
            for mapper in reversed(list(self.iterate_to_root())):
                if mapper.local_table in tables:
                    start = True
                if start and not mapper.single:
                    allconds.append(visitors.cloned_traverse(mapper.inherit_condition, {}, {'binary':visit_binary}))
        except ColumnsNotAvailable:
            return None

        cond = sql.and_(*allconds)
        return sql.select(tables, cond, use_labels=True)

    def cascade_iterator(self, type_, state, halt_on=None):
        """Iterate each element and its mapper in an object graph,
        for all relations that meet the given cascade rule.

        ``type\_``:
          The name of the cascade rule (i.e. save-update, delete,
          etc.)

        ``state``:
          The lead InstanceState.  child items will be processed per
          the relations defined for this object's mapper.

        the return value are object instances; this provides a strong
        reference so that they don't fall out of scope immediately.

        """
        visited_instances = util.IdentitySet()
        visitables = [(self._props.itervalues(), 'property', state)]

        while visitables:
            iterator, item_type, parent_state = visitables[-1]
            try:
                if item_type == 'property':
                    prop = iterator.next()
                    visitables.append((prop.cascade_iterator(type_, parent_state, visited_instances, halt_on), 'mapper', None))
                elif item_type == 'mapper':
                    instance, instance_mapper, corresponding_state  = iterator.next()
                    yield (instance, instance_mapper)
                    visitables.append((instance_mapper._props.itervalues(), 'property', corresponding_state))
            except StopIteration:
                visitables.pop()

    # persistence

    @util.memoized_property
    def _sorted_tables(self):
        table_to_mapper = {}
        for mapper in self.base_mapper.polymorphic_iterator():
            for t in mapper.tables:
                table_to_mapper[t] = mapper
        
        sorted_ = sqlutil.sort_tables(table_to_mapper.iterkeys())
        ret = util.OrderedDict()
        for t in sorted_:
            ret[t] = table_to_mapper[t]
        return ret

    def _save_obj(self, states, uowtransaction, postupdate=False, post_update_cols=None, single=False):
        """Issue ``INSERT`` and/or ``UPDATE`` statements for a list of objects.

        This is called within the context of a UOWTransaction during a
        flush operation.

        `_save_obj` issues SQL statements not just for instances mapped
        directly by this mapper, but for instances mapped by all
        inheriting mappers as well.  This is to maintain proper insert
        ordering among a polymorphic chain of instances. Therefore
        _save_obj is typically called only on a *base mapper*, or a
        mapper which does not inherit from any other mapper.
        
        """
        if self._should_log_debug:
            self._log_debug("_save_obj() start, " + (single and "non-batched" or "batched"))

        # if batch=false, call _save_obj separately for each object
        if not single and not self.batch:
            for state in _sort_states(states):
                self._save_obj([state], uowtransaction, postupdate=postupdate, post_update_cols=post_update_cols, single=True)
            return

        # if session has a connection callable,
        # organize individual states with the connection to use for insert/update
        tups = []
        if 'connection_callable' in uowtransaction.mapper_flush_opts:
            connection_callable = uowtransaction.mapper_flush_opts['connection_callable']
            for state in _sort_states(states):
                m = _state_mapper(state)
                tups.append(
                    (
                        state, 
                        m, 
                        connection_callable(self, state.obj()), 
                        _state_has_identity(state), 
                        state.key or m._identity_key_from_state(state)
                    )
                )
        else:
            connection = uowtransaction.transaction.connection(self)
            for state in _sort_states(states):
                m = _state_mapper(state)
                tups.append(
                    (
                        state, 
                        m, 
                        connection,
                        _state_has_identity(state), 
                        state.key or m._identity_key_from_state(state)
                    )
                )

        if not postupdate:
            # call before_XXX extensions
            for state, mapper, connection, has_identity, instance_key in tups:
                if not has_identity:
                    if 'before_insert' in mapper.extension:
                        mapper.extension.before_insert(mapper, connection, state.obj())
                else:
                    if 'before_update' in mapper.extension:
                        mapper.extension.before_update(mapper, connection, state.obj())

        row_switches = set()
        if not postupdate:
            for state, mapper, connection, has_identity, instance_key in tups:
                # detect if we have a "pending" instance (i.e. has no instance_key attached to it),
                # and another instance with the same identity key already exists as persistent.  convert to an
                # UPDATE if so.
                if not has_identity and instance_key in uowtransaction.session.identity_map:
                    instance = uowtransaction.session.identity_map[instance_key]
                    existing = attributes.instance_state(instance)
                    if not uowtransaction.is_deleted(existing):
                        raise exc.FlushError(
                            "New instance %s with identity key %s conflicts with persistent instance %s" % 
                            (state_str(state), instance_key, state_str(existing)))
                    if self._should_log_debug:
                        self._log_debug(
                            "detected row switch for identity %s.  will update %s, remove %s from transaction", 
                            instance_key, state_str(state), state_str(existing))
                            
                    # remove the "delete" flag from the existing element
                    uowtransaction.set_row_switch(existing)
                    row_switches.add(state)
        
        table_to_mapper = self._sorted_tables

        for table in table_to_mapper.iterkeys():
            insert = []
            update = []

            for state, mapper, connection, has_identity, instance_key in tups:
                if table not in mapper._pks_by_table:
                    continue
                    
                pks = mapper._pks_by_table[table]
                
                if self._should_log_debug:
                    self._log_debug("_save_obj() table '%s' instance %s identity %s" % (table.name, state_str(state), str(instance_key)))

                isinsert = not has_identity and not postupdate and state not in row_switches
                
                params = {}
                value_params = {}
                hasdata = False

                if isinsert:
                    for col in mapper._cols_by_table[table]:
                        if col is mapper.version_id_col:
                            params[col.key] = 1
                        elif mapper.polymorphic_on and mapper.polymorphic_on.shares_lineage(col):
                            if self._should_log_debug:
                                self._log_debug("Using polymorphic identity '%s' for insert column '%s'" % (mapper.polymorphic_identity, col.key))
                            value = mapper.polymorphic_identity
                            if ((col.default is None and
                                 col.server_default is None) or
                                value is not None):
                                params[col.key] = value
                        elif col in pks:
                            value = mapper._get_state_attr_by_column(state, col)
                            if value is not None:
                                params[col.key] = value
                        else:
                            value = mapper._get_state_attr_by_column(state, col)
                            if ((col.default is None and
                                 col.server_default is None) or
                                value is not None):
                                if isinstance(value, sql.ClauseElement):
                                    value_params[col] = value
                                else:
                                    params[col.key] = value
                    insert.append((state, params, mapper, connection, value_params))
                else:
                    for col in mapper._cols_by_table[table]:
                        if col is mapper.version_id_col:
                            params[col._label] = mapper._get_state_attr_by_column(state, col)
                            params[col.key] = params[col._label] + 1
                            for prop in mapper._columntoproperty.itervalues():
                                history = attributes.get_state_history(state, prop.key, passive=True)
                                if history.added:
                                    hasdata = True
                        elif mapper.polymorphic_on and mapper.polymorphic_on.shares_lineage(col):
                            pass
                        else:
                            if post_update_cols is not None and col not in post_update_cols:
                                if col in pks:
                                    params[col._label] = mapper._get_state_attr_by_column(state, col)
                                continue

                            prop = mapper._columntoproperty[col]
                            history = attributes.get_state_history(state, prop.key, passive=True)
                            if history.added:
                                if isinstance(history.added[0], sql.ClauseElement):
                                    value_params[col] = history.added[0]
                                else:
                                    params[col.key] = prop.get_col_value(col, history.added[0])
                                if col in pks:
                                    if history.deleted:
                                        params[col._label] = prop.get_col_value(col, history.deleted[0])
                                        hasdata = True
                                    else:
                                        # row switch logic can reach us here
                                        # remove the pk from the update params so the update doesn't
                                        # attempt to include the pk in the update statement
                                        del params[col.key]
                                        params[col._label] = prop.get_col_value(col, history.added[0])
                                else:
                                    hasdata = True
                            elif col in pks:
                                params[col._label] = mapper._get_state_attr_by_column(state, col)
                    if hasdata:
                        update.append((state, params, mapper, connection, value_params))

            if update:
                mapper = table_to_mapper[table]
                clause = sql.and_()

                for col in mapper._pks_by_table[table]:
                    clause.clauses.append(col == sql.bindparam(col._label, type_=col.type))

                if mapper.version_id_col and table.c.contains_column(mapper.version_id_col):
                    clause.clauses.append(mapper.version_id_col == sql.bindparam(mapper.version_id_col._label, type_=col.type))

                statement = table.update(clause)
                rows = 0
                for state, params, mapper, connection, value_params in update:
                    c = connection.execute(statement.values(value_params), params)
                    mapper._postfetch(uowtransaction, connection, table, state, c, c.last_updated_params(), value_params)

                    rows += c.rowcount

                if c.supports_sane_rowcount() and rows != len(update):
                    raise exc.ConcurrentModificationError("Updated rowcount %d does not match number of objects updated %d" % (rows, len(update)))

            if insert:
                statement = table.insert()
                for state, params, mapper, connection, value_params in insert:
                    c = connection.execute(statement.values(value_params), params)
                    primary_key = c.last_inserted_ids()

                    if primary_key is not None:
                        # set primary key attributes
                        for i, col in enumerate(mapper._pks_by_table[table]):
                            if mapper._get_state_attr_by_column(state, col) is None and len(primary_key) > i:
                                mapper._set_state_attr_by_column(state, col, primary_key[i])
                    mapper._postfetch(uowtransaction, connection, table, state, c, c.last_inserted_params(), value_params)

                    # synchronize newly inserted ids from one table to the next
                    # TODO: this performs some unnecessary attribute transfers
                    # from an attribute to itself, since the attribute is often mapped
                    # to multiple, equivalent columns.  it also may fire off more
                    # than needed overall.
                    for m in mapper.iterate_to_root():
                        if m._inherits_equated_pairs:
                            sync.populate(state, m, state, m, m._inherits_equated_pairs)

        if not postupdate:
            for state, mapper, connection, has_identity, instance_key in tups:

                # expire readonly attributes
                readonly = state.unmodified.intersection(
                    p.key for p in mapper._readonly_props
                )

                if readonly:
                    _expire_state(state, readonly)

                # if specified, eagerly refresh whatever has
                # been expired.
                if self.eager_defaults and state.unloaded:
                    state.key = self._identity_key_from_state(state)
                    uowtransaction.session.query(self)._get(
                        state.key, refresh_state=state,
                        only_load_props=state.unloaded)

                # call after_XXX extensions
                if not has_identity:
                    if 'after_insert' in mapper.extension:
                        mapper.extension.after_insert(mapper, connection, state.obj())
                else:
                    if 'after_update' in mapper.extension:
                        mapper.extension.after_update(mapper, connection, state.obj())

    def _postfetch(self, uowtransaction, connection, table, state, resultproxy, params, value_params):
        """Expire attributes in need of newly persisted database state."""

        postfetch_cols = resultproxy.postfetch_cols()
        generated_cols = list(resultproxy.prefetch_cols())

        if self.polymorphic_on:
            po = table.corresponding_column(self.polymorphic_on)
            if po:
                generated_cols.append(po)

        if self.version_id_col:
            generated_cols.append(self.version_id_col)

        for c in generated_cols:
            if c.key in params and c in self._columntoproperty:
                self._set_state_attr_by_column(state, c, params[c.key])

        deferred_props = [prop.key for prop in [self._columntoproperty[c] for c in postfetch_cols]]

        if deferred_props:
            _expire_state(state, deferred_props)

    def _delete_obj(self, states, uowtransaction):
        """Issue ``DELETE`` statements for a list of objects.

        This is called within the context of a UOWTransaction during a
        flush operation.

        """
        if self._should_log_debug:
            self._log_debug("_delete_obj() start")

        if 'connection_callable' in uowtransaction.mapper_flush_opts:
            connection_callable = uowtransaction.mapper_flush_opts['connection_callable']
            tups = [(state, _state_mapper(state), connection_callable(self, state.obj())) for state in _sort_states(states)]
        else:
            connection = uowtransaction.transaction.connection(self)
            tups = [(state, _state_mapper(state), connection) for state in _sort_states(states)]

        for state, mapper, connection in tups:
            if 'before_delete' in mapper.extension:
                mapper.extension.before_delete(mapper, connection, state.obj())

        table_to_mapper = self._sorted_tables

        for table in reversed(table_to_mapper.keys()):
            delete = {}
            for state, mapper, connection in tups:
                if table not in mapper._pks_by_table:
                    continue

                params = {}
                if not _state_has_identity(state):
                    continue
                else:
                    delete.setdefault(connection, []).append(params)
                for col in mapper._pks_by_table[table]:
                    params[col.key] = mapper._get_state_attr_by_column(state, col)
                if mapper.version_id_col and table.c.contains_column(mapper.version_id_col):
                    params[mapper.version_id_col.key] = mapper._get_state_attr_by_column(state, mapper.version_id_col)

            for connection, del_objects in delete.iteritems():
                mapper = table_to_mapper[table]
                clause = sql.and_()
                for col in mapper._pks_by_table[table]:
                    clause.clauses.append(col == sql.bindparam(col.key, type_=col.type))
                if mapper.version_id_col and table.c.contains_column(mapper.version_id_col):
                    clause.clauses.append(
                        mapper.version_id_col == 
                        sql.bindparam(mapper.version_id_col.key, type_=mapper.version_id_col.type))
                statement = table.delete(clause)
                c = connection.execute(statement, del_objects)
                if c.supports_sane_multi_rowcount() and c.rowcount != len(del_objects):
                    raise exc.ConcurrentModificationError("Deleted rowcount %d does not match "
                            "number of objects deleted %d" % (c.rowcount, len(del_objects)))

        for state, mapper, connection in tups:
            if 'after_delete' in mapper.extension:
                mapper.extension.after_delete(mapper, connection, state.obj())

    def _register_dependencies(self, uowcommit):
        """Register ``DependencyProcessor`` instances with a
        ``unitofwork.UOWTransaction``.

        This call `register_dependencies` on all attached
        ``MapperProperty`` instances.
        
        """
        for dep in self._props.values() + self._dependency_processors:
            dep.register_dependencies(uowcommit)

    def _register_processors(self, uowcommit):
        for dep in self._props.values() + self._dependency_processors:
            dep.register_processors(uowcommit)

    # result set conversion

    def _instance_processor(self, context, path, adapter, polymorphic_from=None, extension=None, only_load_props=None, refresh_state=None, polymorphic_discriminator=None):
        """Produce a mapper level row processor callable which processes rows into mapped instances."""
        
        pk_cols = self.primary_key

        if polymorphic_from or refresh_state:
            polymorphic_on = None
        else:
            polymorphic_on = polymorphic_discriminator or self.polymorphic_on
            polymorphic_instances = util.PopulateDict(self._configure_subclass_mapper(context, path, adapter))

        version_id_col = self.version_id_col

        if adapter:
            pk_cols = [adapter.columns[c] for c in pk_cols]
            if polymorphic_on:
                polymorphic_on = adapter.columns[polymorphic_on]
            if version_id_col:
                version_id_col = adapter.columns[version_id_col]

        identity_class = self._identity_class
        def identity_key(row):
            return (identity_class, tuple(row[column] for column in pk_cols))

        new_populators = []
        existing_populators = []

        def populate_state(state, dict_, row, isnew, only_load_props, **flags):
            if isnew:
                if context.options:
                    state.load_options = context.options
                if state.load_options:
                    state.load_path = context.query._current_path + path

            if not new_populators:
                new_populators[:], existing_populators[:] = self._populators(context, path, row, adapter)

            if isnew:
                populators = new_populators
            else:
                populators = existing_populators

            if only_load_props:
                populators = [p for p in populators if p[0] in only_load_props]

            for key, populator in populators:
                populator(state, dict_, row, isnew=isnew, **flags)

        session_identity_map = context.session.identity_map

        if not extension:
            extension = self.extension

        translate_row = extension.get('translate_row', None)
        create_instance = extension.get('create_instance', None)
        populate_instance = extension.get('populate_instance', None)
        append_result = extension.get('append_result', None)
        populate_existing = context.populate_existing or self.always_refresh

        def _instance(row, result):
            if translate_row:
                ret = translate_row(self, context, row)
                if ret is not EXT_CONTINUE:
                    row = ret

            if polymorphic_on:
                discriminator = row[polymorphic_on]
                if discriminator is not None:
                    _instance = polymorphic_instances[discriminator]
                    if _instance:
                        return _instance(row, result)

            # determine identity key
            if refresh_state:
                identitykey = refresh_state.key
                if identitykey is None:
                    # super-rare condition; a refresh is being called
                    # on a non-instance-key instance; this is meant to only
                    # occur within a flush()
                    identitykey = self._identity_key_from_state(refresh_state)
            else:
                identitykey = identity_key(row)

            if identitykey in session_identity_map:
                instance = session_identity_map[identitykey]
                state = attributes.instance_state(instance)
                dict_ = attributes.instance_dict(instance)

                if self._should_log_debug:
                    self._log_debug("_instance(): using existing instance %s identity %s",
                                        instance_str(instance), identitykey)

                isnew = state.runid != context.runid
                currentload = not isnew
                loaded_instance = False

                if not currentload and version_id_col and context.version_check and \
                        self._get_state_attr_by_column(state, self.version_id_col) != row[version_id_col]:
                    raise exc.ConcurrentModificationError(
                            "Instance '%s' version of %s does not match %s" 
                            % (state_str(state), self._get_state_attr_by_column(state, self.version_id_col), row[version_id_col]))
            elif refresh_state:
                # out of band refresh_state detected (i.e. its not in the session.identity_map)
                # honor it anyway.  this can happen if a _get() occurs within save_obj(), such as
                # when eager_defaults is True.
                state = refresh_state
                instance = state.obj()
                dict_ = attributes.instance_dict(instance)
                isnew = state.runid != context.runid
                currentload = True
                loaded_instance = False
            else:
                if self._should_log_debug:
                    self._log_debug("_instance(): identity key %s not in session", identitykey)

                if self.allow_null_pks:
                    for x in identitykey[1]:
                        if x is not None:
                            break
                    else:
                        return None
                else:
                    if None in identitykey[1]:
                        return None
                isnew = True
                currentload = True
                loaded_instance = True

                if create_instance:
                    instance = create_instance(self, context, row, self.class_)
                    if instance is EXT_CONTINUE:
                        instance = self.class_manager.new_instance()
                    else:
                        manager = attributes.manager_of_class(instance.__class__)
                        # TODO: if manager is None, raise a friendly error about
                        # returning instances of unmapped types
                        manager.setup_instance(instance)
                else:
                    instance = self.class_manager.new_instance()

                if self._should_log_debug:
                    self._log_debug("_instance(): created new instance %s identity %s",
                                instance_str(instance), identitykey)

                dict_ = attributes.instance_dict(instance)
                state = attributes.instance_state(instance)
                state.key = identitykey

                # manually adding instance to session.  for a complete add,
                # session._finalize_loaded() must be called.
                state.session_id = context.session.hash_key
                session_identity_map.add(state)

            if currentload or populate_existing:
                if isnew:
                    state.runid = context.runid
                    context.progress[state] = dict_

                if not populate_instance or \
                        populate_instance(self, context, row, instance, 
                            only_load_props=only_load_props, instancekey=identitykey, isnew=isnew) is EXT_CONTINUE:
                    populate_state(state, dict_, row, isnew, only_load_props)

            else:
                # populate attributes on non-loading instances which have been expired
                # TODO: apply eager loads to un-lazy loaded collections ?
                if state in context.partials or state.unloaded:

                    if state in context.partials:
                        isnew = False
                        (d_, attrs) = context.partials[state]
                    else:
                        isnew = True
                        attrs = state.unloaded
                        context.partials[state] = (dict_, attrs)  #<-- allow query.instances to commit the subset of attrs

                    if not populate_instance or \
                            populate_instance(self, context, row, instance, 
                                only_load_props=attrs, instancekey=identitykey, isnew=isnew) is EXT_CONTINUE:
                        populate_state(state, dict_, row, isnew, attrs, instancekey=identitykey)

            if loaded_instance:
                state._run_on_load(instance)

            if result is not None and \
                        (not append_result or 
                            append_result(self, context, row, instance, result, instancekey=identitykey, isnew=isnew) is EXT_CONTINUE):
                result.append(instance)

            return instance
        return _instance

    def _populators(self, context, path, row, adapter):
        """Produce a collection of attribute level row processor callables."""
        
        new_populators, existing_populators = [], []
        for prop in self._props.itervalues():
            newpop, existingpop = prop.create_row_processor(context, path, self, row, adapter)
            if newpop:
                new_populators.append((prop.key, newpop))
            if existingpop:
                existing_populators.append((prop.key, existingpop))
        return new_populators, existing_populators

    def _configure_subclass_mapper(self, context, path, adapter):
        """Produce a mapper level row processor callable factory for mappers inheriting this one."""
        
        def configure_subclass_mapper(discriminator):
            try:
                mapper = self.polymorphic_map[discriminator]
            except KeyError:
                raise AssertionError("No such polymorphic_identity %r is defined" % discriminator)
            if mapper is self:
                return None
            return mapper._instance_processor(context, path, adapter, polymorphic_from=self)
        return configure_subclass_mapper

log.class_logger(Mapper)


def reconstructor(fn):
    """Decorate a method as the 'reconstructor' hook.

    Designates a method as the "reconstructor", an ``__init__``-like
    method that will be called by the ORM after the instance has been
    loaded from the database or otherwise reconstituted.

    The reconstructor will be invoked with no arguments.  Scalar
    (non-collection) database-mapped attributes of the instance will
    be available for use within the function.  Eagerly-loaded
    collections are generally not yet available and will usually only
    contain the first element.  ORM state changes made to objects at
    this stage will not be recorded for the next flush() operation, so
    the activity within a reconstructor should be conservative.

    """
    fn.__sa_reconstructor__ = True
    return fn

def validates(*names):
    """Decorate a method as a 'validator' for one or more named properties.

    Designates a method as a validator, a method which receives the
    name of the attribute as well as a value to be assigned, or in the
    case of a collection to be added to the collection.  The function
    can then raise validation exceptions to halt the process from continuing,
    or can modify or replace the value before proceeding.   The function
    should otherwise return the given value.

    """
    def wrap(fn):
        fn.__sa_validators__ = names
        return fn
    return wrap

def _event_on_init(state, instance, args, kwargs):
    """Trigger mapper compilation and run init_instance hooks."""

    instrumenting_mapper = state.manager.info[_INSTRUMENTOR]
    # compile() always compiles all mappers
    instrumenting_mapper.compile()
    if 'init_instance' in instrumenting_mapper.extension:
        instrumenting_mapper.extension.init_instance(
            instrumenting_mapper, instrumenting_mapper.class_,
            state.manager.events.original_init,
            instance, args, kwargs)

def _event_on_init_failure(state, instance, args, kwargs):
    """Run init_failed hooks."""

    instrumenting_mapper = state.manager.info[_INSTRUMENTOR]
    if 'init_failed' in instrumenting_mapper.extension:
        util.warn_exception(
            instrumenting_mapper.extension.init_failed,
            instrumenting_mapper, instrumenting_mapper.class_,
            state.manager.events.original_init, instance, args, kwargs)

def _event_on_resurrect(state, instance):
    # re-populate the primary key elements
    # of the dict based on the mapping.
    instrumenting_mapper = state.manager.info[_INSTRUMENTOR]
    for col, val in zip(instrumenting_mapper.primary_key, state.key[1]):
        instrumenting_mapper._set_state_attr_by_column(state, col, val)
    
    
def _sort_states(states):
    return sorted(states, key=operator.attrgetter('sort_key'))

def _load_scalar_attributes(state, attribute_names):
    """initiate a column-based attribute refresh operation."""
    
    mapper = _state_mapper(state)
    session = _state_session(state)
    if not session:
        raise sa_exc.UnboundExecutionError("Instance %s is not bound to a Session; "
                    "attribute refresh operation cannot proceed" % (state_str(state)))

    has_key = _state_has_identity(state)

    result = False
    if mapper.inherits and not mapper.concrete:
        statement = mapper._optimized_get_statement(state, attribute_names)
        if statement:
            result = session.query(mapper).from_statement(statement)._get(None, only_load_props=attribute_names, refresh_state=state)

    if result is False:
        if has_key:
            identity_key = state.key
        else:
            identity_key = mapper._identity_key_from_state(state)
        result = session.query(mapper)._get(identity_key, refresh_state=state, only_load_props=attribute_names)

    # if instance is pending, a refresh operation may not complete (even if PK attributes are assigned)
    if has_key and result is None:
        raise exc.ObjectDeletedError("Instance '%s' has been deleted." % state_str(state))
