# orm/interfaces.py
# Copyright (C) 2005-2013 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
"""
Contains various base classes used throughout the ORM.
Defines the now deprecated ORM extension classes as well
as ORM internals.
Other than the deprecated extensions, this module and the
classes within should be considered mostly private.
"""
from __future__ import absolute_import
from .. import exc as sa_exc, util, inspect
from ..sql import operators
from collections import deque
orm_util = util.importlater('sqlalchemy.orm', 'util')
collections = util.importlater('sqlalchemy.orm', 'collections')
__all__ = (
'AttributeExtension',
'EXT_CONTINUE',
'EXT_STOP',
'ExtensionOption',
'InstrumentationManager',
'LoaderStrategy',
'MapperExtension',
'MapperOption',
'MapperProperty',
'PropComparator',
'PropertyOption',
'SessionExtension',
'StrategizedOption',
'StrategizedProperty',
)
EXT_CONTINUE = util.symbol('EXT_CONTINUE')
EXT_STOP = util.symbol('EXT_STOP')
ONETOMANY = util.symbol('ONETOMANY')
MANYTOONE = util.symbol('MANYTOONE')
MANYTOMANY = util.symbol('MANYTOMANY')
from .deprecated_interfaces import AttributeExtension, \
SessionExtension, \
MapperExtension
NOT_EXTENSION = util.symbol('NOT_EXTENSION')
"""Symbol indicating an :class:`_InspectionAttr` that's
not part of sqlalchemy.ext.
Is assigned to the :attr:`._InspectionAttr.extension_type`
attibute.
"""
class _InspectionAttr(object):
"""A base class applied to all ORM objects that can be returned
by the :func:`.inspect` function.
The attributes defined here allow the usage of simple boolean
checks to test basic facts about the object returned.
While the boolean checks here are basically the same as using
the Python isinstance() function, the flags here can be used without
the need to import all of these classes, and also such that
the SQLAlchemy class system can change while leaving the flags
here intact for forwards-compatibility.
"""
is_selectable = False
"""Return True if this object is an instance of :class:`.Selectable`."""
is_aliased_class = False
"""True if this object is an instance of :class:`.AliasedClass`."""
is_instance = False
"""True if this object is an instance of :class:`.InstanceState`."""
is_mapper = False
"""True if this object is an instance of :class:`.Mapper`."""
is_property = False
"""True if this object is an instance of :class:`.MapperProperty`."""
is_attribute = False
"""True if this object is a Python :term:`descriptor`.
This can refer to one of many types. Usually a
:class:`.QueryableAttribute` which handles attributes events on behalf
of a :class:`.MapperProperty`. But can also be an extension type
such as :class:`.AssociationProxy` or :class:`.hybrid_property`.
The :attr:`._InspectionAttr.extension_type` will refer to a constant
identifying the specific subtype.
.. seealso::
:attr:`.Mapper.all_orm_descriptors`
"""
is_clause_element = False
"""True if this object is an instance of :class:`.ClauseElement`."""
extension_type = NOT_EXTENSION
"""The extension type, if any.
Defaults to :data:`.interfaces.NOT_EXTENSION`
.. versionadded:: 0.8.0
.. seealso::
:data:`.HYBRID_METHOD`
:data:`.HYBRID_PROPERTY`
:data:`.ASSOCIATION_PROXY`
"""
class _MappedAttribute(object):
"""Mixin for attributes which should be replaced by mapper-assigned
attributes.
"""
class MapperProperty(_MappedAttribute, _InspectionAttr):
"""Manage the relationship of a ``Mapper`` to a single class
attribute, as well as that attribute as it appears on individual
instances of the class, including attribute instrumentation,
attribute access, loading behavior, and dependency calculations.
The most common occurrences of :class:`.MapperProperty` are the
mapped :class:`.Column`, which is represented in a mapping as
an instance of :class:`.ColumnProperty`,
and a reference to another class produced by :func:`.relationship`,
represented in the mapping as an instance of
:class:`.RelationshipProperty`.
"""
cascade = frozenset()
"""The set of 'cascade' attribute names.
This collection is checked before the 'cascade_iterator' method is called.
"""
is_property = True
def setup(self, context, entity, path, adapter, **kwargs):
"""Called by Query for the purposes of constructing a SQL statement.
Each MapperProperty associated with the target mapper processes the
statement referenced by the query context, adding columns and/or
criterion as appropriate.
"""
pass
def create_row_processor(self, context, path,
mapper, row, adapter):
"""Return a 3-tuple consisting of three row processing functions.
"""
return None, None, None
def cascade_iterator(self, type_, state, visited_instances=None,
halt_on=None):
"""Iterate through instances related to the given instance for
a particular 'cascade', starting with this MapperProperty.
Return an iterator3-tuples (instance, mapper, state).
Note that the 'cascade' collection on this MapperProperty is
checked first for the given type before cascade_iterator is called.
See PropertyLoader for the related instance implementation.
"""
return iter(())
def set_parent(self, parent, init):
self.parent = parent
def instrument_class(self, mapper): # pragma: no-coverage
raise NotImplementedError()
@util.memoized_property
def info(self):
"""Info dictionary associated with the object, allowing user-defined
data to be associated with this :class:`.MapperProperty`.
The dictionary is generated when first accessed. Alternatively,
it can be specified as a constructor argument to the
:func:`.column_property`, :func:`.relationship`, or :func:`.composite`
functions.
.. versionadded:: 0.8 Added support for .info to all
:class:`.MapperProperty` subclasses.
.. seealso::
:attr:`.QueryableAttribute.info`
:attr:`.SchemaItem.info`
"""
return {}
_configure_started = False
_configure_finished = False
def init(self):
"""Called after all mappers are created to assemble
relationships between mappers and perform other post-mapper-creation
initialization steps.
"""
self._configure_started = True
self.do_init()
self._configure_finished = True
@property
def class_attribute(self):
"""Return the class-bound descriptor corresponding to this
:class:`.MapperProperty`.
This is basically a ``getattr()`` call::
return getattr(self.parent.class_, self.key)
I.e. if this :class:`.MapperProperty` were named ``addresses``,
and the class to which it is mapped is ``User``, this sequence
is possible::
>>> from sqlalchemy import inspect
>>> mapper = inspect(User)
>>> addresses_property = mapper.attrs.addresses
>>> addresses_property.class_attribute is User.addresses
True
>>> User.addresses.property is addresses_property
True
"""
return getattr(self.parent.class_, self.key)
def do_init(self):
"""Perform subclass-specific initialization post-mapper-creation
steps.
This is a template method called by the ``MapperProperty``
object's init() method.
"""
pass
def post_instrument_class(self, mapper):
"""Perform instrumentation adjustments that need to occur
after init() has completed.
"""
pass
def is_primary(self):
"""Return True if this ``MapperProperty``'s mapper is the
primary mapper for its class.
This flag is used to indicate that the ``MapperProperty`` can
define attribute instrumentation for the class at the class
level (as opposed to the individual instance level).
"""
return not self.parent.non_primary
def merge(self, session, source_state, source_dict, dest_state,
dest_dict, load, _recursive):
"""Merge the attribute represented by this ``MapperProperty``
from source to destination object"""
pass
def compare(self, operator, value, **kw):
"""Return a compare operation for the columns represented by
this ``MapperProperty`` to the given value, which may be a
column value or an instance. 'operator' is an operator from
the operators module, or from sql.Comparator.
By default uses the PropComparator attached to this MapperProperty
under the attribute name "comparator".
"""
return operator(self.comparator, value)
def __repr__(self):
return '<%s at 0x%x; %s>' % (
self.__class__.__name__,
id(self), getattr(self, 'key', 'no key'))
class PropComparator(operators.ColumnOperators):
"""Defines boolean, comparison, and other operators for
:class:`.MapperProperty` objects.
SQLAlchemy allows for operators to
be redefined at both the Core and ORM level. :class:`.PropComparator`
is the base class of operator redefinition for ORM-level operations,
including those of :class:`.ColumnProperty`,
:class:`.RelationshipProperty`, and :class:`.CompositeProperty`.
.. note:: With the advent of Hybrid properties introduced in SQLAlchemy
0.7, as well as Core-level operator redefinition in
SQLAlchemy 0.8, the use case for user-defined :class:`.PropComparator`
instances is extremely rare. See :ref:`hybrids_toplevel` as well
as :ref:`types_operators`.
User-defined subclasses of :class:`.PropComparator` may be created. The
built-in Python comparison and math operator methods, such as
:meth:`.operators.ColumnOperators.__eq__`,
:meth:`.operators.ColumnOperators.__lt__`, and
:meth:`.operators.ColumnOperators.__add__`, can be overridden to provide
new operator behavior. The custom :class:`.PropComparator` is passed to
the :class:`.MapperProperty` instance via the ``comparator_factory``
argument. In each case,
the appropriate subclass of :class:`.PropComparator` should be used::
# definition of custom PropComparator subclasses
from sqlalchemy.orm.properties import \\
ColumnProperty,\\
CompositeProperty,\\
RelationshipProperty
class MyColumnComparator(ColumnProperty.Comparator):
def __eq__(self, other):
return self.__clause_element__() == other
class MyRelationshipComparator(RelationshipProperty.Comparator):
def any(self, expression):
"define the 'any' operation"
# ...
class MyCompositeComparator(CompositeProperty.Comparator):
def __gt__(self, other):
"redefine the 'greater than' operation"
return sql.and_(*[a>b for a, b in
zip(self.__clause_element__().clauses,
other.__composite_values__())])
# application of custom PropComparator subclasses
from sqlalchemy.orm import column_property, relationship, composite
from sqlalchemy import Column, String
class SomeMappedClass(Base):
some_column = column_property(Column("some_column", String),
comparator_factory=MyColumnComparator)
some_relationship = relationship(SomeOtherClass,
comparator_factory=MyRelationshipComparator)
some_composite = composite(
Column("a", String), Column("b", String),
comparator_factory=MyCompositeComparator
)
Note that for column-level operator redefinition, it's usually
simpler to define the operators at the Core level, using the
:attr:`.TypeEngine.comparator_factory` attribute. See
:ref:`types_operators` for more detail.
See also:
:class:`.ColumnProperty.Comparator`
:class:`.RelationshipProperty.Comparator`
:class:`.CompositeProperty.Comparator`
:class:`.ColumnOperators`
:ref:`types_operators`
:attr:`.TypeEngine.comparator_factory`
"""
def __init__(self, prop, parentmapper, adapter=None):
self.prop = self.property = prop
self._parentmapper = parentmapper
self.adapter = adapter
def __clause_element__(self):
raise NotImplementedError("%r" % self)
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.prop, self._parentmapper, adapter)
@util.memoized_property
def info(self):
return self.property.info
@staticmethod
def any_op(a, b, **kwargs):
return a.any(b, **kwargs)
@staticmethod
def has_op(a, b, **kwargs):
return a.has(b, **kwargs)
@staticmethod
def of_type_op(a, class_):
return a.of_type(class_)
def of_type(self, class_):
"""Redefine this object in terms of a polymorphic subclass.
Returns a new PropComparator from which further criterion can be
evaluated.
e.g.::
query.join(Company.employees.of_type(Engineer)).\\
filter(Engineer.name=='foo')
:param \class_: a class or mapper indicating that criterion will be
against this specific subclass.
"""
return self.operate(PropComparator.of_type_op, class_)
def any(self, criterion=None, **kwargs):
"""Return true if this collection contains any member that meets the
given criterion.
The usual implementation of ``any()`` is
:meth:`.RelationshipProperty.Comparator.any`.
:param criterion: an optional ClauseElement formulated against the
member class' table or attributes.
:param \**kwargs: key/value pairs corresponding to member class
attribute names which will be compared via equality to the
corresponding values.
"""
return self.operate(PropComparator.any_op, criterion, **kwargs)
def has(self, criterion=None, **kwargs):
"""Return true if this element references a member which meets the
given criterion.
The usual implementation of ``has()`` is
:meth:`.RelationshipProperty.Comparator.has`.
:param criterion: an optional ClauseElement formulated against the
member class' table or attributes.
:param \**kwargs: key/value pairs corresponding to member class
attribute names which will be compared via equality to the
corresponding values.
"""
return self.operate(PropComparator.has_op, criterion, **kwargs)
class StrategizedProperty(MapperProperty):
"""A MapperProperty which uses selectable strategies to affect
loading behavior.
There is a single strategy selected by default. Alternate
strategies can be selected at Query time through the usage of
``StrategizedOption`` objects via the Query.options() method.
"""
strategy_wildcard_key = None
@util.memoized_property
def _wildcard_path(self):
if self.strategy_wildcard_key:
return ('loaderstrategy', (self.strategy_wildcard_key,))
else:
return None
def _get_context_strategy(self, context, path):
strategy_cls = path._inlined_get_for(self, context, 'loaderstrategy')
if not strategy_cls:
wc_key = self._wildcard_path
if wc_key and wc_key in context.attributes:
strategy_cls = context.attributes[wc_key]
if strategy_cls:
try:
return self._strategies[strategy_cls]
except KeyError:
return self.__init_strategy(strategy_cls)
return self.strategy
def _get_strategy(self, cls):
try:
return self._strategies[cls]
except KeyError:
return self.__init_strategy(cls)
def __init_strategy(self, cls):
self._strategies[cls] = strategy = cls(self)
return strategy
def setup(self, context, entity, path, adapter, **kwargs):
self._get_context_strategy(context, path).\
setup_query(context, entity, path,
adapter, **kwargs)
def create_row_processor(self, context, path, mapper, row, adapter):
return self._get_context_strategy(context, path).\
create_row_processor(context, path,
mapper, row, adapter)
def do_init(self):
self._strategies = {}
self.strategy = self.__init_strategy(self.strategy_class)
def post_instrument_class(self, mapper):
if self.is_primary() and \
not mapper.class_manager._attr_has_impl(self.key):
self.strategy.init_class_attribute(mapper)
class MapperOption(object):
"""Describe a modification to a Query."""
propagate_to_loaders = False
"""if True, indicate this option should be carried along
Query object generated by scalar or object lazy loaders.
"""
def process_query(self, query):
pass
def process_query_conditionally(self, query):
"""same as process_query(), except that this option may not
apply to the given query.
Used when secondary loaders resend existing options to a new
Query."""
self.process_query(query)
class PropertyOption(MapperOption):
"""A MapperOption that is applied to a property off the mapper or
one of its child mappers, identified by a dot-separated key
or list of class-bound attributes. """
def __init__(self, key, mapper=None):
self.key = key
self.mapper = mapper
def process_query(self, query):
self._process(query, True)
def process_query_conditionally(self, query):
self._process(query, False)
def _process(self, query, raiseerr):
paths = self._process_paths(query, raiseerr)
if paths:
self.process_query_property(query, paths)
def process_query_property(self, query, paths):
pass
def __getstate__(self):
d = self.__dict__.copy()
d['key'] = ret = []
for token in util.to_list(self.key):
if isinstance(token, PropComparator):
ret.append((token._parentmapper.class_, token.key))
else:
ret.append(token)
return d
def __setstate__(self, state):
ret = []
for key in state['key']:
if isinstance(key, tuple):
cls, propkey = key
ret.append(getattr(cls, propkey))
else:
ret.append(key)
state['key'] = tuple(ret)
self.__dict__ = state
def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
if orm_util._is_aliased_class(mapper):
searchfor = mapper
else:
searchfor = orm_util._class_to_mapper(mapper)
for ent in query._mapper_entities:
if ent.corresponds_to(searchfor):
return ent
else:
if raiseerr:
if not list(query._mapper_entities):
raise sa_exc.ArgumentError(
"Query has only expression-based entities - "
"can't find property named '%s'."
% (token, )
)
else:
raise sa_exc.ArgumentError(
"Can't find property '%s' on any entity "
"specified in this Query. Note the full path "
"from root (%s) to target entity must be specified."
% (token, ",".join(str(x) for
x in query._mapper_entities))
)
else:
return None
def _find_entity_basestring(self, query, token, raiseerr):
for ent in query._mapper_entities:
# return only the first _MapperEntity when searching
# based on string prop name. Ideally object
# attributes are used to specify more exactly.
return ent
else:
if raiseerr:
raise sa_exc.ArgumentError(
"Query has only expression-based entities - "
"can't find property named '%s'."
% (token, )
)
else:
return None
def _process_paths(self, query, raiseerr):
"""reconcile the 'key' for this PropertyOption with
the current path and entities of the query.
Return a list of affected paths.
"""
path = orm_util.PathRegistry.root
entity = None
paths = []
no_result = []
# _current_path implies we're in a
# secondary load with an existing path
current_path = list(query._current_path.path)
tokens = deque(self.key)
while tokens:
token = tokens.popleft()
if isinstance(token, basestring):
# wildcard token
if token.endswith(':*'):
return [path.token(token)]
sub_tokens = token.split(".", 1)
token = sub_tokens[0]
tokens.extendleft(sub_tokens[1:])
# exhaust current_path before
# matching tokens to entities
if current_path:
if current_path[1].key == token:
current_path = current_path[2:]
continue
else:
return no_result
if not entity:
entity = self._find_entity_basestring(
query,
token,
raiseerr)
if entity is None:
return no_result
path_element = entity.entity_zero
mapper = entity.mapper
if hasattr(mapper.class_, token):
prop = getattr(mapper.class_, token).property
else:
if raiseerr:
raise sa_exc.ArgumentError(
"Can't find property named '%s' on the "
"mapped entity %s in this Query. " % (
token, mapper)
)
else:
return no_result
elif isinstance(token, PropComparator):
prop = token.property
# exhaust current_path before
# matching tokens to entities
if current_path:
if current_path[0:2] == \
[token._parententity, prop]:
current_path = current_path[2:]
continue
else:
return no_result
if not entity:
entity = self._find_entity_prop_comparator(
query,
prop.key,
token._parententity,
raiseerr)
if not entity:
return no_result
path_element = entity.entity_zero
mapper = entity.mapper
else:
raise sa_exc.ArgumentError(
"mapper option expects "
"string key or list of attributes")
assert prop is not None
if raiseerr and not prop.parent.common_parent(mapper):
raise sa_exc.ArgumentError("Attribute '%s' does not "
"link from element '%s'" % (token, path_element))
path = path[path_element][prop]
paths.append(path)
if getattr(token, '_of_type', None):
ac = token._of_type
ext_info = inspect(ac)
path_element = mapper = ext_info.mapper
if not ext_info.is_aliased_class:
ac = orm_util.with_polymorphic(
ext_info.mapper.base_mapper,
ext_info.mapper, aliased=True,
_use_mapper_path=True)
ext_info = inspect(ac)
path.set(query, "path_with_polymorphic", ext_info)
else:
path_element = mapper = getattr(prop, 'mapper', None)
if mapper is None and tokens:
raise sa_exc.ArgumentError(
"Attribute '%s' of entity '%s' does not "
"refer to a mapped entity" %
(token, entity)
)
if current_path:
# ran out of tokens before
# current_path was exhausted.
assert not tokens
return no_result
return paths
class StrategizedOption(PropertyOption):
"""A MapperOption that affects which LoaderStrategy will be used
for an operation by a StrategizedProperty.
"""
chained = False
def process_query_property(self, query, paths):
strategy = self.get_strategy_class()
if self.chained:
for path in paths:
path.set(
query,
"loaderstrategy",
strategy
)
else:
paths[-1].set(
query,
"loaderstrategy",
strategy
)
def get_strategy_class(self):
raise NotImplementedError()
class LoaderStrategy(object):
"""Describe the loading behavior of a StrategizedProperty object.
The ``LoaderStrategy`` interacts with the querying process in three
ways:
* it controls the configuration of the ``InstrumentedAttribute``
placed on a class to handle the behavior of the attribute. this
may involve setting up class-level callable functions to fire
off a select operation when the attribute is first accessed
(i.e. a lazy load)
* it processes the ``QueryContext`` at statement construction time,
where it can modify the SQL statement that is being produced.
Simple column attributes may add their represented column to the
list of selected columns, *eager loading* properties may add
``LEFT OUTER JOIN`` clauses to the statement.
* It produces "row processor" functions at result fetching time.
These "row processor" functions populate a particular attribute
on a particular mapped instance.
"""
def __init__(self, parent):
self.parent_property = parent
self.is_class_level = False
self.parent = self.parent_property.parent
self.key = self.parent_property.key
def init_class_attribute(self, mapper):
pass
def setup_query(self, context, entity, path, adapter, **kwargs):
pass
def create_row_processor(self, context, path, mapper,
row, adapter):
"""Return row processing functions which fulfill the contract
specified by MapperProperty.create_row_processor.
StrategizedProperty delegates its create_row_processor method
directly to this method. """
return None, None, None
def __str__(self):
return str(self.parent_property)