# orm/properties.py
# Copyright (C) 2005-2012 the SQLAlchemy authors and contributors <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""MapperProperty implementations.

This is a private module which defines the behavior of invidual ORM-
mapped attributes.

"""

from sqlalchemy import sql, util, log, exc as sa_exc
from sqlalchemy.sql.util import ClauseAdapter, criterion_as_pairs, \
    join_condition, _shallow_annotate
from sqlalchemy.sql import operators, expression
from sqlalchemy.orm import attributes, dependency, mapper, \
    object_mapper, strategies, configure_mappers
from sqlalchemy.orm.util import CascadeOptions, _class_to_mapper, \
    _orm_annotate, _orm_deannotate

from sqlalchemy.orm.interfaces import MANYTOMANY, MANYTOONE, \
    MapperProperty, ONETOMANY, PropComparator, StrategizedProperty
mapperlib = util.importlater("sqlalchemy.orm", "mapperlib")
NoneType = type(None)

__all__ = ('ColumnProperty', 'CompositeProperty', 'SynonymProperty',
           'ComparableProperty', 'RelationshipProperty', 'RelationProperty')

from descriptor_props import CompositeProperty, SynonymProperty, \
            ComparableProperty,ConcreteInheritedProperty

class ColumnProperty(StrategizedProperty):
    """Describes an object attribute that corresponds to a table column.
    
    Public constructor is the :func:`.orm.column_property` function.
    
    """

    def __init__(self, *columns, **kwargs):
        """Construct a ColumnProperty.

        Note the public constructor is the :func:`.orm.column_property` function.

        :param \*columns: The list of `columns` describes a single
          object property. If there are multiple tables joined
          together for the mapper, this list represents the equivalent
          column as it appears across each table.

        :param group:

        :param deferred:

        :param comparator_factory:

        :param descriptor:

        :param expire_on_flush:

        :param extension:

        """
        self._orig_columns = [expression._labeled(c) for c in columns]
        self.columns = [expression._labeled(_orm_deannotate(c)) 
                            for c in columns]
        self.group = kwargs.pop('group', None)
        self.deferred = kwargs.pop('deferred', False)
        self.instrument = kwargs.pop('_instrument', True)
        self.comparator_factory = kwargs.pop('comparator_factory',
                                            self.__class__.Comparator)
        self.descriptor = kwargs.pop('descriptor', None)
        self.extension = kwargs.pop('extension', None)
        self.active_history = kwargs.pop('active_history', False)
        self.expire_on_flush = kwargs.pop('expire_on_flush', True)

        if 'doc' in kwargs:
            self.doc = kwargs.pop('doc')
        else:
            for col in reversed(self.columns):
                doc = getattr(col, 'doc', None)
                if doc is not None:
                    self.doc = doc
                    break
            else:
                self.doc = None

        if kwargs:
            raise TypeError(
                "%s received unexpected keyword argument(s): %s" % (
                    self.__class__.__name__, 
                    ', '.join(sorted(kwargs.keys()))))

        util.set_creation_order(self)
        if not self.instrument:
            self.strategy_class = strategies.UninstrumentedColumnLoader
        elif self.deferred:
            self.strategy_class = strategies.DeferredColumnLoader
        else:
            self.strategy_class = strategies.ColumnLoader

    def instrument_class(self, mapper):
        if not self.instrument:
            return

        attributes.register_descriptor(
            mapper.class_, 
            self.key, 
            comparator=self.comparator_factory(self, mapper), 
            parententity=mapper,
            doc=self.doc
            )

    def do_init(self):
        super(ColumnProperty, self).do_init()
        if len(self.columns) > 1 and \
                set(self.parent.primary_key).issuperset(self.columns):
            util.warn(
                ("On mapper %s, primary key column '%s' is being combined "
                 "with distinct primary key column '%s' in attribute '%s'.  "
                 "Use explicit properties to give each column its own mapped "
                 "attribute name.") % (self.parent, self.columns[1],
                                       self.columns[0], self.key))

    def copy(self):
        return ColumnProperty(
                        deferred=self.deferred, 
                        group=self.group, 
                        active_history=self.active_history,
                        *self.columns)

    def _getcommitted(self, state, dict_, column, 
                    passive=attributes.PASSIVE_OFF):
        return state.get_impl(self.key).\
                    get_committed_value(state, dict_, passive=passive)

    def merge(self, session, source_state, source_dict, dest_state, 
                                dest_dict, load, _recursive):
        if not self.instrument:
            return
        elif self.key in source_dict:
            value = source_dict[self.key]

            if not load:
                dest_dict[self.key] = value
            else:
                impl = dest_state.get_impl(self.key)
                impl.set(dest_state, dest_dict, value, None)
        elif dest_state.has_identity and self.key not in dest_dict:
            dest_state.expire_attributes(dest_dict, [self.key])

    class Comparator(PropComparator):
        @util.memoized_instancemethod
        def __clause_element__(self):
            if self.adapter:
                return self.adapter(self.prop.columns[0])
            else:
                return self.prop.columns[0]._annotate({
                                                "parententity": self.mapper,
                                                "parentmapper":self.mapper})

        def operate(self, op, *other, **kwargs):
            return op(self.__clause_element__(), *other, **kwargs)

        def reverse_operate(self, op, other, **kwargs):
            col = self.__clause_element__()
            return op(col._bind_param(op, other), col, **kwargs)

    # TODO: legacy..do we need this ? (0.5)
    ColumnComparator = Comparator

    def __str__(self):
        return str(self.parent.class_.__name__) + "." + self.key

log.class_logger(ColumnProperty)

class RelationshipProperty(StrategizedProperty):
    """Describes an object property that holds a single item or list
    of items that correspond to a related database table.
    
    Public constructor is the :func:`.orm.relationship` function.
    
    Of note here is the :class:`.RelationshipProperty.Comparator`
    class, which implements comparison operations for scalar-
    and collection-referencing mapped attributes.
    
    """

    strategy_wildcard_key = 'relationship:*'

    def __init__(self, argument,
        secondary=None, primaryjoin=None,
        secondaryjoin=None, 
        foreign_keys=None,
        uselist=None,
        order_by=False,
        backref=None,
        back_populates=None,
        post_update=False,
        cascade=False, extension=None,
        viewonly=False, lazy=True,
        collection_class=None, passive_deletes=False,
        passive_updates=True, remote_side=None,
        enable_typechecks=True, join_depth=None,
        comparator_factory=None,
        single_parent=False, innerjoin=False,
        doc=None,
        active_history=False,
        cascade_backrefs=True,
        load_on_pending=False,
        strategy_class=None, _local_remote_pairs=None, 
        query_class=None):

        self.uselist = uselist
        self.argument = argument
        self.secondary = secondary
        self.primaryjoin = primaryjoin
        self.secondaryjoin = secondaryjoin
        self.post_update = post_update
        self.direction = None
        self.viewonly = viewonly
        self.lazy = lazy
        self.single_parent = single_parent
        self._user_defined_foreign_keys = foreign_keys
        self.collection_class = collection_class
        self.passive_deletes = passive_deletes
        self.cascade_backrefs = cascade_backrefs
        self.passive_updates = passive_updates
        self.remote_side = remote_side
        self.enable_typechecks = enable_typechecks
        self.query_class = query_class
        self.innerjoin = innerjoin
        self.doc = doc
        self.active_history = active_history
        self.join_depth = join_depth
        self.local_remote_pairs = _local_remote_pairs
        self.extension = extension
        self.load_on_pending = load_on_pending
        self.comparator_factory = comparator_factory or \
                                    RelationshipProperty.Comparator
        self.comparator = self.comparator_factory(self, None)
        util.set_creation_order(self)

        if strategy_class:
            self.strategy_class = strategy_class
        elif self.lazy== 'dynamic':
            from sqlalchemy.orm import dynamic
            self.strategy_class = dynamic.DynaLoader
        else:
            self.strategy_class = strategies.factory(self.lazy)

        self._reverse_property = set()

        if cascade is not False:
            self.cascade = CascadeOptions(cascade)
        else:
            self.cascade = CascadeOptions("save-update, merge")

        if self.passive_deletes == 'all' and \
                    ("delete" in self.cascade or 
                    "delete-orphan" in self.cascade):
            raise sa_exc.ArgumentError(
                            "Can't set passive_deletes='all' in conjunction "
                            "with 'delete' or 'delete-orphan' cascade")

        self.order_by = order_by

        self.back_populates = back_populates

        if self.back_populates:
            if backref:
                raise sa_exc.ArgumentError(
                            "backref and back_populates keyword arguments "
                            "are mutually exclusive")
            self.backref = None
        else:
            self.backref = backref


    def instrument_class(self, mapper):
        attributes.register_descriptor(
            mapper.class_, 
            self.key, 
            comparator=self.comparator_factory(self, mapper), 
            parententity=mapper,
            doc=self.doc,
            )

    class Comparator(PropComparator):
        """Produce comparison operations for :func:`~.orm.relationship`-based
         attributes."""

        def __init__(self, prop, mapper, of_type=None, adapter=None):
            """Construction of :class:`.RelationshipProperty.Comparator`
            is internal to the ORM's attribute mechanics.
            
            """
            self.prop = prop
            self.mapper = mapper
            self.adapter = adapter
            if of_type:
                self._of_type = _class_to_mapper(of_type)

        def adapted(self, adapter):
            """Return a copy of this PropComparator which will use the
            given adaption function on the local side of generated
            expressions.

            """

            return self.__class__(self.property, self.mapper,
                                  getattr(self, '_of_type', None),
                                  adapter)

        @property
        def parententity(self):
            return self.property.parent

        def __clause_element__(self):
            elem = self.property.parent._with_polymorphic_selectable
            if self.adapter:
                return self.adapter(elem)
            else:
                return elem

        def of_type(self, cls):
            """Produce a construct that represents a particular 'subtype' of
            attribute for the parent class.
            
            Currently this is usable in conjunction with :meth:`.Query.join`
            and :meth:`.Query.outerjoin`.
            
            """
            return RelationshipProperty.Comparator(
                                        self.property, 
                                        self.mapper, 
                                        cls, adapter=self.adapter)

        def in_(self, other):
            """Produce an IN clause - this is not implemented 
            for :func:`~.orm.relationship`-based attributes at this time.
            
            """
            raise NotImplementedError('in_() not yet supported for '
                    'relationships.  For a simple many-to-one, use '
                    'in_() against the set of foreign key values.')

        __hash__ = None

        def __eq__(self, other):
            """Implement the ``==`` operator.

            In a many-to-one context, such as::

              MyClass.some_prop == <some object>

            this will typically produce a
            clause such as::
  
              mytable.related_id == <some id>
  
            Where ``<some id>`` is the primary key of the given 
            object.
  
            The ``==`` operator provides partial functionality for non-
            many-to-one comparisons:
  
            * Comparisons against collections are not supported.
              Use :meth:`~.RelationshipProperty.Comparator.contains`.
            * Compared to a scalar one-to-many, will produce a 
              clause that compares the target columns in the parent to
              the given target. 
            * Compared to a scalar many-to-many, an alias
              of the association table will be rendered as
              well, forming a natural join that is part of the
              main body of the query. This will not work for
              queries that go beyond simple AND conjunctions of
              comparisons, such as those which use OR. Use
              explicit joins, outerjoins, or
              :meth:`~.RelationshipProperty.Comparator.has` for
              more comprehensive non-many-to-one scalar
              membership tests.
            * Comparisons against ``None`` given in a one-to-many
              or many-to-many context produce a NOT EXISTS clause.

            """
            if isinstance(other, (NoneType, expression._Null)):
                if self.property.direction in [ONETOMANY, MANYTOMANY]:
                    return ~self._criterion_exists()
                else:
                    return _orm_annotate(self.property._optimized_compare(
                            None, adapt_source=self.adapter))
            elif self.property.uselist:
                raise sa_exc.InvalidRequestError("Can't compare a colle"
                        "ction to an object or collection; use "
                        "contains() to test for membership.")
            else:
                return _orm_annotate(self.property._optimized_compare(other,
                        adapt_source=self.adapter))

        def _criterion_exists(self, criterion=None, **kwargs):
            if getattr(self, '_of_type', None):
                target_mapper = self._of_type
                to_selectable = target_mapper._with_polymorphic_selectable
                if self.property._is_self_referential:
                    to_selectable = to_selectable.alias()

                single_crit = target_mapper._single_table_criterion
                if single_crit is not None:
                    if criterion is not None:
                        criterion = single_crit & criterion
                    else:
                        criterion = single_crit
            else:
                to_selectable = None

            if self.adapter:
                source_selectable = self.__clause_element__()
            else:
                source_selectable = None

            pj, sj, source, dest, secondary, target_adapter = \
                self.property._create_joins(dest_polymorphic=True,
                        dest_selectable=to_selectable,
                        source_selectable=source_selectable)

            for k in kwargs:
                crit = getattr(self.property.mapper.class_, k) == kwargs[k]
                if criterion is None:
                    criterion = crit
                else:
                    criterion = criterion & crit

            # annotate the *local* side of the join condition, in the case
            # of pj + sj this is the full primaryjoin, in the case of just
            # pj its the local side of the primaryjoin.
            if sj is not None:
                j = _orm_annotate(pj) & sj
            else:
                j = _orm_annotate(pj, exclude=self.property.remote_side)

            if criterion is not None and target_adapter:
                # limit this adapter to annotated only?
                criterion = target_adapter.traverse(criterion)

            # only have the "joined left side" of what we 
            # return be subject to Query adaption.  The right
            # side of it is used for an exists() subquery and 
            # should not correlate or otherwise reach out
            # to anything in the enclosing query.
            if criterion is not None:
                criterion = criterion._annotate({'no_replacement_traverse': True})

            crit = j & criterion

            return sql.exists([1], crit, from_obj=dest).\
                            correlate(source._annotate({'_orm_adapt':True}))

        def any(self, criterion=None, **kwargs):
            """Produce an expression that tests a collection against
            particular criterion, using EXISTS.
            
            An expression like::
            
                session.query(MyClass).filter(
                    MyClass.somereference.any(SomeRelated.x==2)
                )
                
                
            Will produce a query like::
            
                SELECT * FROM my_table WHERE
                EXISTS (SELECT 1 FROM related WHERE related.my_id=my_table.id 
                AND related.x=2)
                
            Because :meth:`~.RelationshipProperty.Comparator.any` uses
            a correlated subquery, its performance is not nearly as
            good when compared against large target tables as that of
            using a join.
            
            :meth:`~.RelationshipProperty.Comparator.any` is particularly
            useful for testing for empty collections::
            
                session.query(MyClass).filter(
                    ~MyClass.somereference.any()
                )
            
            will produce::
            
                SELECT * FROM my_table WHERE
                NOT EXISTS (SELECT 1 FROM related WHERE related.my_id=my_table.id)
                
            :meth:`~.RelationshipProperty.Comparator.any` is only
            valid for collections, i.e. a :func:`.relationship`
            that has ``uselist=True``.  For scalar references,
            use :meth:`~.RelationshipProperty.Comparator.has`.
            
            """
            if not self.property.uselist:
                raise sa_exc.InvalidRequestError(
                            "'any()' not implemented for scalar "
                            "attributes. Use has()."
                        )

            return self._criterion_exists(criterion, **kwargs)

        def has(self, criterion=None, **kwargs):
            """Produce an expression that tests a scalar reference against
            particular criterion, using EXISTS.

            An expression like::
            
                session.query(MyClass).filter(
                    MyClass.somereference.has(SomeRelated.x==2)
                )
                
                
            Will produce a query like::
            
                SELECT * FROM my_table WHERE
                EXISTS (SELECT 1 FROM related WHERE related.id==my_table.related_id
                AND related.x=2)

            Because :meth:`~.RelationshipProperty.Comparator.has` uses
            a correlated subquery, its performance is not nearly as
            good when compared against large target tables as that of
            using a join.
            
            :meth:`~.RelationshipProperty.Comparator.has` is only
            valid for scalar references, i.e. a :func:`.relationship`
            that has ``uselist=False``.  For collection references,
            use :meth:`~.RelationshipProperty.Comparator.any`.
            
            """
            if self.property.uselist:
                raise sa_exc.InvalidRequestError(
                            "'has()' not implemented for collections.  "
                            "Use any().")
            return self._criterion_exists(criterion, **kwargs)

        def contains(self, other, **kwargs):
            """Return a simple expression that tests a collection for 
            containment of a particular item.
            
            :meth:`~.RelationshipProperty.Comparator.contains` is
            only valid for a collection, i.e. a
            :func:`~.orm.relationship` that implements
            one-to-many or many-to-many with ``uselist=True``.
            
            When used in a simple one-to-many context, an 
            expression like::
            
                MyClass.contains(other)
                
            Produces a clause like::
            
                mytable.id == <some id>
                
            Where ``<some id>`` is the value of the foreign key
            attribute on ``other`` which refers to the primary
            key of its parent object. From this it follows that
            :meth:`~.RelationshipProperty.Comparator.contains` is
            very useful when used with simple one-to-many
            operations.
            
            For many-to-many operations, the behavior of
            :meth:`~.RelationshipProperty.Comparator.contains`
            has more caveats. The association table will be
            rendered in the statement, producing an "implicit"
            join, that is, includes multiple tables in the FROM
            clause which are equated in the WHERE clause::
            
                query(MyClass).filter(MyClass.contains(other))
                
            Produces a query like::
            
                SELECT * FROM my_table, my_association_table AS
                my_association_table_1 WHERE
                my_table.id = my_association_table_1.parent_id
                AND my_association_table_1.child_id = <some id>
                
            Where ``<some id>`` would be the primary key of
            ``other``. From the above, it is clear that
            :meth:`~.RelationshipProperty.Comparator.contains`
            will **not** work with many-to-many collections when
            used in queries that move beyond simple AND
            conjunctions, such as multiple
            :meth:`~.RelationshipProperty.Comparator.contains`
            expressions joined by OR. In such cases subqueries or
            explicit "outer joins" will need to be used instead.
            See :meth:`~.RelationshipProperty.Comparator.any` for
            a less-performant alternative using EXISTS, or refer
            to :meth:`.Query.outerjoin` as well as :ref:`ormtutorial_joins`
            for more details on constructing outer joins.
            
            """
            if not self.property.uselist:
                raise sa_exc.InvalidRequestError(
                            "'contains' not implemented for scalar "
                            "attributes.  Use ==")
            clause = self.property._optimized_compare(other,
                    adapt_source=self.adapter)

            if self.property.secondaryjoin is not None:
                clause.negation_clause = \
                    self.__negated_contains_or_equals(other)

            return clause

        def __negated_contains_or_equals(self, other):
            if self.property.direction == MANYTOONE:
                state = attributes.instance_state(other)

                def state_bindparam(x, state, col):
                    o = state.obj() # strong ref
                    return sql.bindparam(x, unique=True, callable_=lambda : \
                        self.property.mapper._get_committed_attr_by_column(o,
                            col))

                def adapt(col):
                    if self.adapter:
                        return self.adapter(col)
                    else:
                        return col

                if self.property._use_get:
                    return sql.and_(*[
                        sql.or_(
                        adapt(x) != state_bindparam(adapt(x), state, y),
                        adapt(x) == None)
                        for (x, y) in self.property.local_remote_pairs])

            criterion = sql.and_(*[x==y for (x, y) in 
                                zip(
                                    self.property.mapper.primary_key,
                                    self.property.\
                                            mapper.\
                                            primary_key_from_instance(other))
                                    ])
            return ~self._criterion_exists(criterion)

        def __ne__(self, other):
            """Implement the ``!=`` operator.

            In a many-to-one context, such as::
  
              MyClass.some_prop != <some object>
  
            This will typically produce a clause such as::
  
              mytable.related_id != <some id>
  
            Where ``<some id>`` is the primary key of the
            given object.
  
            The ``!=`` operator provides partial functionality for non-
            many-to-one comparisons:
  
            * Comparisons against collections are not supported.
              Use
              :meth:`~.RelationshipProperty.Comparator.contains`
              in conjunction with :func:`~.expression.not_`.
            * Compared to a scalar one-to-many, will produce a 
              clause that compares the target columns in the parent to
              the given target. 
            * Compared to a scalar many-to-many, an alias
              of the association table will be rendered as
              well, forming a natural join that is part of the
              main body of the query. This will not work for
              queries that go beyond simple AND conjunctions of
              comparisons, such as those which use OR. Use
              explicit joins, outerjoins, or
              :meth:`~.RelationshipProperty.Comparator.has` in
              conjunction with :func:`~.expression.not_` for
              more comprehensive non-many-to-one scalar
              membership tests.
            * Comparisons against ``None`` given in a one-to-many
              or many-to-many context produce an EXISTS clause.
                
            """
            if isinstance(other, (NoneType, expression._Null)):
                if self.property.direction == MANYTOONE:
                    return sql.or_(*[x != None for x in
                                   self.property._calculated_foreign_keys])
                else:
                    return self._criterion_exists()
            elif self.property.uselist:
                raise sa_exc.InvalidRequestError("Can't compare a collection"
                        " to an object or collection; use "
                        "contains() to test for membership.")
            else:
                return self.__negated_contains_or_equals(other)

        @util.memoized_property
        def property(self):
            if mapperlib.module._new_mappers:
                configure_mappers()
            return self.prop

    def compare(self, op, value, 
                            value_is_parent=False, 
                            alias_secondary=True):
        if op == operators.eq:
            if value is None:
                if self.uselist:
                    return ~sql.exists([1], self.primaryjoin)
                else:
                    return self._optimized_compare(None, 
                                    value_is_parent=value_is_parent,
                                    alias_secondary=alias_secondary)
            else:
                return self._optimized_compare(value, 
                                value_is_parent=value_is_parent,
                                alias_secondary=alias_secondary)
        else:
            return op(self.comparator, value)

    def _optimized_compare(self, value, value_is_parent=False, 
                                    adapt_source=None, 
                                    alias_secondary=True):
        if value is not None:
            value = attributes.instance_state(value)
        return self._get_strategy(strategies.LazyLoader).lazy_clause(value,
                reverse_direction=not value_is_parent,
                alias_secondary=alias_secondary,
                adapt_source=adapt_source)

    def __str__(self):
        return str(self.parent.class_.__name__) + "." + self.key

    def merge(self, 
                    session,
                    source_state,
                    source_dict,
                    dest_state,
                    dest_dict, 
                    load, _recursive):

        if load:
            for r in self._reverse_property:
                if (source_state, r) in _recursive:
                    return


        if not "merge" in self.cascade:
            return

        if self.key not in source_dict:
            return

        if self.uselist:
            instances = source_state.get_impl(self.key).\
                            get(source_state, source_dict)
            if hasattr(instances, '_sa_adapter'):
                # convert collections to adapters to get a true iterator
                instances = instances._sa_adapter

            if load:
                # for a full merge, pre-load the destination collection,
                # so that individual _merge of each item pulls from identity
                # map for those already present.
                # also assumes CollectionAttrbiuteImpl behavior of loading
                # "old" list in any case
                dest_state.get_impl(self.key).get(dest_state, dest_dict)

            dest_list = []
            for current in instances:
                current_state = attributes.instance_state(current)
                current_dict = attributes.instance_dict(current)
                _recursive[(current_state, self)] = True
                obj = session._merge(current_state, current_dict,
                        load=load, _recursive=_recursive)
                if obj is not None:
                    dest_list.append(obj)

            if not load:
                coll = attributes.init_state_collection(dest_state,
                        dest_dict, self.key)
                for c in dest_list:
                    coll.append_without_event(c)
            else:
                dest_state.get_impl(self.key)._set_iterable(dest_state,
                        dest_dict, dest_list)
        else:
            current = source_dict[self.key]
            if current is not None:
                current_state = attributes.instance_state(current)
                current_dict = attributes.instance_dict(current)
                _recursive[(current_state, self)] = True
                obj = session._merge(current_state, current_dict,
                        load=load, _recursive=_recursive)
            else:
                obj = None

            if not load:
                dest_dict[self.key] = obj
            else:
                dest_state.get_impl(self.key).set(dest_state,
                        dest_dict, obj, None)

    def cascade_iterator(self, type_, state, dict_, visited_states, halt_on=None):
        #assert type_ in self.cascade

        # only actively lazy load on the 'delete' cascade
        if type_ != 'delete' or self.passive_deletes:
            passive = attributes.PASSIVE_NO_INITIALIZE
        else:
            passive = attributes.PASSIVE_OFF

        if type_ == 'save-update':
            tuples = state.manager[self.key].impl.\
                        get_all_pending(state, dict_)

        else:
            tuples = state.value_as_iterable(dict_, self.key,
                            passive=passive)

        skip_pending = type_ == 'refresh-expire' and 'delete-orphan' \
            not in self.cascade

        for instance_state, c in tuples:
            if instance_state in visited_states:
                continue

            if c is None:
                # would like to emit a warning here, but
                # would not be consistent with collection.append(None)
                # current behavior of silently skipping.
                # see [ticket:2229]
                continue

            instance_dict = attributes.instance_dict(c)

            if halt_on and halt_on(instance_state):
                continue

            if skip_pending and not instance_state.key:
                continue

            instance_mapper = instance_state.manager.mapper

            if not instance_mapper.isa(self.mapper.class_manager.mapper):
                raise AssertionError("Attribute '%s' on class '%s' "
                                    "doesn't handle objects "
                                    "of type '%s'" % (
                                        self.key, 
                                        self.parent.class_, 
                                        c.__class__
                                    ))

            visited_states.add(instance_state)

            yield c, instance_mapper, instance_state, instance_dict


    def _add_reverse_property(self, key):
        other = self.mapper.get_property(key, _compile_mappers=False)
        self._reverse_property.add(other)
        other._reverse_property.add(self)

        if not other.mapper.common_parent(self.parent):
            raise sa_exc.ArgumentError('reverse_property %r on '
                    'relationship %s references relationship %s, which '
                    'does not reference mapper %s' % (key, self, other,
                    self.parent))
        if self.direction in (ONETOMANY, MANYTOONE) and self.direction \
            == other.direction:
            raise sa_exc.ArgumentError('%s and back-reference %s are '
                    'both of the same direction %r.  Did you mean to '
                    'set remote_side on the many-to-one side ?'
                    % (other, self, self.direction))

    @util.memoized_property
    def mapper(self):
        """Return the targeted :class:`.Mapper` for this 
        :class:`.RelationshipProperty`.
        
        This is a lazy-initializing static attribute.
        
        """
        if isinstance(self.argument, type):
            mapper_ = mapper.class_mapper(self.argument,
                    compile=False)
        elif isinstance(self.argument, mapper.Mapper):
            mapper_ = self.argument
        elif util.callable(self.argument):

            # accept a callable to suit various deferred-
            # configurational schemes

            mapper_ = mapper.class_mapper(self.argument(),
                    compile=False)
        else:
            raise sa_exc.ArgumentError("relationship '%s' expects "
                    "a class or a mapper argument (received: %s)"
                    % (self.key, type(self.argument)))
        assert isinstance(mapper_, mapper.Mapper), mapper_
        return mapper_

    @util.memoized_property
    @util.deprecated("0.7", "Use .target")
    def table(self):
        """Return the selectable linked to this 
        :class:`.RelationshipProperty` object's target 
        :class:`.Mapper`."""
        return self.target

    def do_init(self):
        self._check_conflicts()
        self._process_dependent_arguments()
        self._determine_joins()
        self._determine_synchronize_pairs()
        self._determine_direction()
        self._determine_local_remote_pairs()
        self._post_init()
        self._generate_backref()
        super(RelationshipProperty, self).do_init()

    def _check_conflicts(self):
        """Test that this relationship is legal, warn about 
        inheritance conflicts."""

        if not self.is_primary() \
            and not mapper.class_mapper(
                                self.parent.class_,
                                compile=False).has_property(self.key):
            raise sa_exc.ArgumentError("Attempting to assign a new "
                    "relationship '%s' to a non-primary mapper on "
                    "class '%s'.  New relationships can only be added "
                    "to the primary mapper, i.e. the very first mapper "
                    "created for class '%s' " % (self.key,
                    self.parent.class_.__name__,
                    self.parent.class_.__name__))

        # check for conflicting relationship() on superclass
        if not self.parent.concrete:
            for inheriting in self.parent.iterate_to_root():
                if inheriting is not self.parent \
                    and inheriting.has_property(self.key):
                    util.warn("Warning: relationship '%s' on mapper "
                              "'%s' supersedes the same relationship "
                              "on inherited mapper '%s'; this can "
                              "cause dependency issues during flush"
                              % (self.key, self.parent, inheriting))

    def _process_dependent_arguments(self):
        """Convert incoming configuration arguments to their 
        proper form.
        
        Callables are resolved, ORM annotations removed.
        
        """
        # accept callables for other attributes which may require
        # deferred initialization.  This technique is used
        # by declarative "string configs" and some recipes.
        for attr in (
            'order_by',
            'primaryjoin',
            'secondaryjoin',
            'secondary',
            '_user_defined_foreign_keys',
            'remote_side',
            ):
            attr_value = getattr(self, attr)
            if util.callable(attr_value):
                setattr(self, attr, attr_value())

        # remove "annotations" which are present if mapped class
        # descriptors are used to create the join expression.
        for attr in 'primaryjoin', 'secondaryjoin':
            val = getattr(self, attr)
            if val is not None:
                setattr(self, attr, _orm_deannotate(
                    expression._only_column_elements(val, attr))
                )

        # ensure expressions in self.order_by, foreign_keys,
        # remote_side are all columns, not strings.
        if self.order_by is not False and self.order_by is not None:
            self.order_by = [
                    expression._only_column_elements(x, "order_by") 
                    for x in
                    util.to_list(self.order_by)]

        self._user_defined_foreign_keys = \
            util.column_set(
                    expression._only_column_elements(x, "foreign_keys") 
                    for x in util.to_column_set(
                        self._user_defined_foreign_keys
                    ))

        self.remote_side = \
            util.column_set(
                    expression._only_column_elements(x, "remote_side") 
                    for x in
                    util.to_column_set(self.remote_side))

        self.target = self.mapper.mapped_table

        if self.cascade.delete_orphan:
            self.mapper.primary_mapper().delete_orphans.append(
                            (self.key, self.parent.class_)
                        )

    def _determine_joins(self):
        """Determine the 'primaryjoin' and 'secondaryjoin' attributes,
        if not passed to the constructor already.
        
        This is based on analysis of the foreign key relationships
        between the parent and target mapped selectables.
        
        """
        if self.secondaryjoin is not None and self.secondary is None:
            raise sa_exc.ArgumentError("Property '" + self.key
                    + "' specified with secondary join condition but "
                    "no secondary argument")

        # if join conditions were not specified, figure them out based
        # on foreign keys

        def _search_for_join(mapper, table):
            # find a join between the given mapper's mapped table and
            # the given table. will try the mapper's local table first
            # for more specificity, then if not found will try the more
            # general mapped table, which in the case of inheritance is
            # a join.
            return join_condition(mapper.mapped_table, table, 
                                        a_subset=mapper.local_table)

        try:
            if self.secondary is not None:
                if self.secondaryjoin is None:
                    self.secondaryjoin = _search_for_join(self.mapper,
                            self.secondary)
                if self.primaryjoin is None:
                    self.primaryjoin = _search_for_join(self.parent,
                            self.secondary)
            else:
                if self.primaryjoin is None:
                    self.primaryjoin = _search_for_join(self.parent,
                            self.target)
        except sa_exc.ArgumentError, e:
            raise sa_exc.ArgumentError("Could not determine join "
                    "condition between parent/child tables on "
                    "relationship %s.  Specify a 'primaryjoin' "
                    "expression.  If 'secondary' is present, "
                    "'secondaryjoin' is needed as well."
                    % self)

    def _columns_are_mapped(self, *cols):
        """Return True if all columns in the given collection are 
        mapped by the tables referenced by this :class:`.Relationship`.
        
        """
        for c in cols:
            if self.secondary is not None \
                and self.secondary.c.contains_column(c):
                continue
            if not self.parent.mapped_table.c.contains_column(c) and \
                not self.target.c.contains_column(c):
                return False
        return True

    def _sync_pairs_from_join(self, join_condition, primary):
        """Determine a list of "source"/"destination" column pairs
        based on the given join condition, as well as the
        foreign keys argument.
        
        "source" would be a column referenced by a foreign key,
        and "destination" would be the column who has a foreign key
        reference to "source".
        
        """

        fks = self._user_defined_foreign_keys
        # locate pairs
        eq_pairs = criterion_as_pairs(join_condition,
                consider_as_foreign_keys=fks,
                any_operator=self.viewonly)

        # couldn't find any fks, but we have 
        # "secondary" - assume the "secondary" columns
        # are the fks
        if not eq_pairs and \
                self.secondary is not None and \
                not fks:
            fks = set(self.secondary.c)
            eq_pairs = criterion_as_pairs(join_condition,
                    consider_as_foreign_keys=fks,
                    any_operator=self.viewonly)

            if eq_pairs:
                util.warn("No ForeignKey objects were present "
                            "in secondary table '%s'.  Assumed referenced "
                            "foreign key columns %s for join condition '%s' "
                            "on relationship %s" % (
                            self.secondary.description,
                            ", ".join(sorted(["'%s'" % col for col in fks])),
                            join_condition,
                            self
                        ))

        # Filter out just to columns that are mapped.
        # If viewonly, allow pairs where the FK col
        # was part of "foreign keys" - the column it references
        # may be in an un-mapped table - see 
        # test.orm.test_relationships.ViewOnlyComplexJoin.test_basic
        # for an example of this.
        eq_pairs = [(l, r) for (l, r) in eq_pairs
                    if self._columns_are_mapped(l, r)
                    or self.viewonly and 
                    r in fks]

        if eq_pairs:
            return eq_pairs

        # from here below is just determining the best error message
        # to report.  Check for a join condition using any operator 
        # (not just ==), perhaps they need to turn on "viewonly=True".
        if not self.viewonly and criterion_as_pairs(join_condition,
                consider_as_foreign_keys=self._user_defined_foreign_keys,
                any_operator=True):

            err = "Could not locate any "\
                    "foreign-key-equated, locally mapped column "\
                    "pairs for %s "\
                    "condition '%s' on relationship %s." % (
                        primary and 'primaryjoin' or 'secondaryjoin', 
                        join_condition, 
                        self
                    )

            if not self._user_defined_foreign_keys:
                err += "  Ensure that the "\
                        "referencing Column objects have a "\
                        "ForeignKey present, or are otherwise part "\
                        "of a ForeignKeyConstraint on their parent "\
                        "Table, or specify the foreign_keys parameter "\
                        "to this relationship."

            err += "  For more "\
                    "relaxed rules on join conditions, the "\
                    "relationship may be marked as viewonly=True."

            raise sa_exc.ArgumentError(err)
        else:
            if self._user_defined_foreign_keys:
                raise sa_exc.ArgumentError("Could not determine "
                        "relationship direction for %s condition "
                        "'%s', on relationship %s, using manual "
                        "'foreign_keys' setting.  Do the columns "
                        "in 'foreign_keys' represent all, and "
                        "only, the 'foreign' columns in this join "
                        "condition?  Does the %s Table already "
                        "have adequate ForeignKey and/or "
                        "ForeignKeyConstraint objects established "
                        "(in which case 'foreign_keys' is usually "
                        "unnecessary)?" 
                        % (
                            primary and 'primaryjoin' or 'secondaryjoin',
                            join_condition, 
                            self,
                            primary and 'mapped' or 'secondary'
                        ))
            else:
                raise sa_exc.ArgumentError("Could not determine "
                        "relationship direction for %s condition "
                        "'%s', on relationship %s. Ensure that the "
                        "referencing Column objects have a "
                        "ForeignKey present, or are otherwise part "
                        "of a ForeignKeyConstraint on their parent "
                        "Table, or specify the foreign_keys parameter " 
                        "to this relationship."
                        % (
                            primary and 'primaryjoin' or 'secondaryjoin', 
                            join_condition, 
                            self
                        ))

    def _determine_synchronize_pairs(self):
        """Resolve 'primary'/foreign' column pairs from the primaryjoin
        and secondaryjoin arguments.
        
        """
        if self.local_remote_pairs:
            if not self._user_defined_foreign_keys:
                raise sa_exc.ArgumentError(
                        "foreign_keys argument is "
                        "required with _local_remote_pairs argument")
            self.synchronize_pairs = []
            for l, r in self.local_remote_pairs:
                if r in self._user_defined_foreign_keys:
                    self.synchronize_pairs.append((l, r))
                elif l in self._user_defined_foreign_keys:
                    self.synchronize_pairs.append((r, l))
        else:
            self.synchronize_pairs = self._sync_pairs_from_join(
                                                self.primaryjoin, 
                                                True)

        self._calculated_foreign_keys = util.column_set(
                                r for (l, r) in
                                self.synchronize_pairs)

        if self.secondaryjoin is not None:
            self.secondary_synchronize_pairs = self._sync_pairs_from_join(
                                                        self.secondaryjoin, 
                                                        False)
            self._calculated_foreign_keys.update(
                                r for (l, r) in
                                self.secondary_synchronize_pairs)
        else:
            self.secondary_synchronize_pairs = None

    def _determine_direction(self):
        """Determine if this relationship is one to many, many to one, 
        many to many.
        
        This is derived from the primaryjoin, presence of "secondary",
        and in the case of self-referential the "remote side".
        
        """
        if self.secondaryjoin is not None:
            self.direction = MANYTOMANY
        elif self._refers_to_parent_table():

            # self referential defaults to ONETOMANY unless the "remote"
            # side is present and does not reference any foreign key
            # columns

            if self.local_remote_pairs:
                remote = [r for (l, r) in self.local_remote_pairs]
            elif self.remote_side:
                remote = self.remote_side
            else:
                remote = None
            if not remote or self._calculated_foreign_keys.difference(l for (l,
                    r) in self.synchronize_pairs).intersection(remote):
                self.direction = ONETOMANY
            else:
                self.direction = MANYTOONE
        else:
            parentcols = util.column_set(self.parent.mapped_table.c)
            targetcols = util.column_set(self.mapper.mapped_table.c)

            # fk collection which suggests ONETOMANY.
            onetomany_fk = targetcols.intersection(
                            self._calculated_foreign_keys)

            # fk collection which suggests MANYTOONE.

            manytoone_fk = parentcols.intersection(
                            self._calculated_foreign_keys)

            if onetomany_fk and manytoone_fk:
                # fks on both sides.  do the same test only based on the
                # local side.
                referents = [c for (c, f) in self.synchronize_pairs]
                onetomany_local = parentcols.intersection(referents)
                manytoone_local = targetcols.intersection(referents)

                if onetomany_local and not manytoone_local:
                    self.direction = ONETOMANY
                elif manytoone_local and not onetomany_local:
                    self.direction = MANYTOONE
                else:
                    raise sa_exc.ArgumentError(
                            "Can't determine relationship"
                            " direction for relationship '%s' - foreign "
                            "key columns are present in both the parent "
                            "and the child's mapped tables.  Specify "
                            "'foreign_keys' argument." % self)
            elif onetomany_fk:
                self.direction = ONETOMANY
            elif manytoone_fk:
                self.direction = MANYTOONE
            else:
                raise sa_exc.ArgumentError("Can't determine relationship "
                        "direction for relationship '%s' - foreign "
                        "key columns are present in neither the parent "
                        "nor the child's mapped tables" % self)

        if self.cascade.delete_orphan and not self.single_parent \
            and (self.direction is MANYTOMANY or self.direction
                 is MANYTOONE):
            util.warn('On %s, delete-orphan cascade is not supported '
                      'on a many-to-many or many-to-one relationship '
                      'when single_parent is not set.   Set '
                      'single_parent=True on the relationship().'
                      % self)
        if self.direction is MANYTOONE and self.passive_deletes:
            util.warn("On %s, 'passive_deletes' is normally configured "
                      "on one-to-many, one-to-one, many-to-many "
                      "relationships only."
                       % self)

    def _determine_local_remote_pairs(self):
        """Determine pairs of columns representing "local" to 
        "remote", where "local" columns are on the parent mapper,
        "remote" are on the target mapper.
        
        These pairs are used on the load side only to generate
        lazy loading clauses.

        """
        if not self.local_remote_pairs and not self.remote_side:
            # the most common, trivial case.   Derive 
            # local/remote pairs from the synchronize pairs.
            eq_pairs = util.unique_list(
                            self.synchronize_pairs + 
                            (self.secondary_synchronize_pairs or []))
            if self.direction is MANYTOONE:
                self.local_remote_pairs = [(r, l) for l, r in eq_pairs]
            else:
                self.local_remote_pairs = eq_pairs

        # "remote_side" specified, derive from the primaryjoin
        # plus remote_side, similarly to how synchronize_pairs
        # were determined.
        elif self.remote_side:
            if self.local_remote_pairs:
                raise sa_exc.ArgumentError('remote_side argument is '
                    'redundant against more detailed '
                    '_local_remote_side argument.')
            if self.direction is MANYTOONE:
                self.local_remote_pairs = [(r, l) for (l, r) in
                        criterion_as_pairs(self.primaryjoin,
                        consider_as_referenced_keys=self.remote_side,
                        any_operator=True)]

            else:
                self.local_remote_pairs = \
                    criterion_as_pairs(self.primaryjoin,
                        consider_as_foreign_keys=self.remote_side,
                        any_operator=True)
            if not self.local_remote_pairs:
                raise sa_exc.ArgumentError('Relationship %s could '
                        'not determine any local/remote column '
                        'pairs from remote side argument %r'
                        % (self, self.remote_side))
        # else local_remote_pairs were sent explcitly via
        # ._local_remote_pairs.

        # create local_side/remote_side accessors
        self.local_side = util.ordered_column_set(
                            l for l, r in self.local_remote_pairs)
        self.remote_side = util.ordered_column_set(
                            r for l, r in self.local_remote_pairs)

        # check that the non-foreign key column in the local/remote
        # collection is mapped.  The foreign key
        # which the individual mapped column references directly may
        # itself be in a non-mapped table; see
        # test.orm.test_relationships.ViewOnlyComplexJoin.test_basic
        # for an example of this.
        if self.direction is ONETOMANY:
            for col in self.local_side:
                if not self._columns_are_mapped(col):
                    raise sa_exc.ArgumentError(
                            "Local column '%s' is not "
                            "part of mapping %s.  Specify remote_side "
                            "argument to indicate which column lazy join "
                            "condition should compare against." % (col,
                            self.parent))
        elif self.direction is MANYTOONE:
            for col in self.remote_side:
                if not self._columns_are_mapped(col):
                    raise sa_exc.ArgumentError(
                            "Remote column '%s' is not "
                            "part of mapping %s. Specify remote_side "
                            "argument to indicate which column lazy join "
                            "condition should bind." % (col, self.mapper))

    def _generate_backref(self):
        if not self.is_primary():
            return
        if self.backref is not None and not self.back_populates:
            if isinstance(self.backref, basestring):
                backref_key, kwargs = self.backref, {}
            else:
                backref_key, kwargs = self.backref
            mapper = self.mapper.primary_mapper()
            if mapper.has_property(backref_key):
                raise sa_exc.ArgumentError("Error creating backref "
                        "'%s' on relationship '%s': property of that "
                        "name exists on mapper '%s'" % (backref_key,
                        self, mapper))
            if self.secondary is not None:
                pj = kwargs.pop('primaryjoin', self.secondaryjoin)
                sj = kwargs.pop('secondaryjoin', self.primaryjoin)
            else:
                pj = kwargs.pop('primaryjoin', self.primaryjoin)
                sj = kwargs.pop('secondaryjoin', None)
                if sj:
                    raise sa_exc.InvalidRequestError(
                        "Can't assign 'secondaryjoin' on a backref against "
                        "a non-secondary relationship."
                            )
            foreign_keys = kwargs.pop('foreign_keys',
                    self._user_defined_foreign_keys)
            parent = self.parent.primary_mapper()
            kwargs.setdefault('viewonly', self.viewonly)
            kwargs.setdefault('post_update', self.post_update)
            kwargs.setdefault('passive_updates', self.passive_updates)
            self.back_populates = backref_key
            relationship = RelationshipProperty(
                parent,
                self.secondary,
                pj,
                sj,
                foreign_keys=foreign_keys,
                back_populates=self.key,
                **kwargs
                )
            mapper._configure_property(backref_key, relationship)

        if self.back_populates:
            self._add_reverse_property(self.back_populates)

    def _post_init(self):
        self.logger.info('%s setup primary join %s', self,
                         self.primaryjoin)
        self.logger.info('%s setup secondary join %s', self,
                         self.secondaryjoin)
        self.logger.info('%s synchronize pairs [%s]', self,
                         ','.join('(%s => %s)' % (l, r) for (l, r) in
                         self.synchronize_pairs))
        self.logger.info('%s secondary synchronize pairs [%s]', self,
                         ','.join('(%s => %s)' % (l, r) for (l, r) in
                         self.secondary_synchronize_pairs or []))
        self.logger.info('%s local/remote pairs [%s]', self,
                         ','.join('(%s / %s)' % (l, r) for (l, r) in
                         self.local_remote_pairs))
        self.logger.info('%s relationship direction %s', self,
                         self.direction)
        if self.uselist is None:
            self.uselist = self.direction is not MANYTOONE
        if not self.viewonly:
            self._dependency_processor = \
                dependency.DependencyProcessor.from_relationship(self)

    @util.memoized_property
    def _use_get(self):
        """memoize the 'use_get' attribute of this RelationshipLoader's
        lazyloader."""

        strategy = self._get_strategy(strategies.LazyLoader)
        return strategy.use_get

    def _refers_to_parent_table(self):
        pt = self.parent.mapped_table
        mt = self.mapper.mapped_table
        for c, f in self.synchronize_pairs:
            if (
                pt.is_derived_from(c.table) and \
                pt.is_derived_from(f.table) and \
                mt.is_derived_from(c.table) and \
                mt.is_derived_from(f.table)
            ):
                return True
        else:
            return False

    @util.memoized_property
    def _is_self_referential(self):
        return self.mapper.common_parent(self.parent)

    def per_property_preprocessors(self, uow):
        if not self.viewonly and self._dependency_processor:
            self._dependency_processor.per_property_preprocessors(uow)

    def _create_joins(self, source_polymorphic=False, 
                            source_selectable=None, dest_polymorphic=False, 
                            dest_selectable=None, of_type=None):
        if source_selectable is None:
            if source_polymorphic and self.parent.with_polymorphic:
                source_selectable = self.parent._with_polymorphic_selectable

        aliased = False
        if dest_selectable is None:
            if dest_polymorphic and self.mapper.with_polymorphic:
                dest_selectable = self.mapper._with_polymorphic_selectable
                aliased = True
            else:
                dest_selectable = self.mapper.mapped_table

            if self._is_self_referential and source_selectable is None:
                dest_selectable = dest_selectable.alias()
                aliased = True
        else:
            aliased = True

        # place a barrier on the destination such that
        # replacement traversals won't ever dig into it.
        # its internal structure remains fixed 
        # regardless of context.
        dest_selectable = _shallow_annotate(
                                dest_selectable, 
                                {'no_replacement_traverse':True})

        aliased = aliased or (source_selectable is not None)

        primaryjoin, secondaryjoin, secondary = self.primaryjoin, \
            self.secondaryjoin, self.secondary

        # adjust the join condition for single table inheritance,
        # in the case that the join is to a subclass
        # this is analogous to the "_adjust_for_single_table_inheritance()"
        # method in Query.

        dest_mapper = of_type or self.mapper

        single_crit = dest_mapper._single_table_criterion
        if single_crit is not None:
            if secondaryjoin is not None:
                secondaryjoin = secondaryjoin & single_crit
            else:
                primaryjoin = primaryjoin & single_crit

        if aliased:
            if secondary is not None:
                secondary = secondary.alias()
                primary_aliasizer = ClauseAdapter(secondary)
                secondary_aliasizer = \
                    ClauseAdapter(dest_selectable,
                        equivalents=self.mapper._equivalent_columns).\
                        chain(primary_aliasizer)
                if source_selectable is not None:
                    primary_aliasizer = \
                        ClauseAdapter(secondary).\
                            chain(ClauseAdapter(source_selectable,
                            equivalents=self.parent._equivalent_columns))
                secondaryjoin = \
                    secondary_aliasizer.traverse(secondaryjoin)
            else:
                primary_aliasizer = ClauseAdapter(dest_selectable,
                        exclude=self.local_side,
                        equivalents=self.mapper._equivalent_columns)
                if source_selectable is not None:
                    primary_aliasizer.chain(
                        ClauseAdapter(source_selectable,
                            exclude=self.remote_side,
                            equivalents=self.parent._equivalent_columns))
                secondary_aliasizer = None
            primaryjoin = primary_aliasizer.traverse(primaryjoin)
            target_adapter = secondary_aliasizer or primary_aliasizer
            target_adapter.include = target_adapter.exclude = None
        else:
            target_adapter = None
        if source_selectable is None:
            source_selectable = self.parent.local_table
        if dest_selectable is None:
            dest_selectable = self.mapper.local_table
        return (
            primaryjoin,
            secondaryjoin,
            source_selectable,
            dest_selectable,
            secondary,
            target_adapter,
            )

PropertyLoader = RelationProperty = RelationshipProperty
log.class_logger(RelationshipProperty)

