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# orm/interfaces.py
# Copyright (C) 2005-2019 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 some key base classes prominent within the internals,
as well as the now-deprecated ORM extension classes.
Other than the deprecated extensions, this module and the
classes within are mostly private, though some attributes
are exposed when inspecting mappings.
"""
from __future__ import absolute_import
import collections
from . import exc as orm_exc
from . import path_registry
from .base import _MappedAttribute # noqa
from .base import EXT_CONTINUE
from .base import EXT_SKIP
from .base import EXT_STOP
from .base import InspectionAttr # noqa
from .base import InspectionAttrInfo # noqa
from .base import MANYTOMANY
from .base import MANYTOONE
from .base import NOT_EXTENSION
from .base import ONETOMANY
from .. import inspect
from .. import util
from ..sql import operators
# imported later
MapperExtension = SessionExtension = AttributeExtension = None
__all__ = (
"AttributeExtension",
"EXT_CONTINUE",
"EXT_STOP",
"EXT_SKIP",
"ONETOMANY",
"MANYTOMANY",
"MANYTOONE",
"NOT_EXTENSION",
"LoaderStrategy",
"MapperExtension",
"MapperOption",
"MapperProperty",
"PropComparator",
"SessionExtension",
"StrategizedProperty",
)
class MapperProperty(_MappedAttribute, InspectionAttr, util.MemoizedSlots):
"""Represent a particular class attribute mapped by :class:`.Mapper`.
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`.
"""
__slots__ = (
"_configure_started",
"_configure_finished",
"parent",
"key",
"info",
)
cascade = frozenset()
"""The set of 'cascade' attribute names.
This collection is checked before the 'cascade_iterator' method is called.
The collection typically only applies to a RelationshipProperty.
"""
is_property = True
"""Part of the InspectionAttr interface; states this object is a
mapper property.
"""
def _memoized_attr_info(self):
"""Info dictionary associated with the object, allowing user-defined
data to be associated with this :class:`.InspectionAttr`.
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.
.. versionchanged:: 1.0.0 :attr:`.MapperProperty.info` is also
available on extension types via the
:attr:`.InspectionAttrInfo.info` attribute, so that it can apply
to a wider variety of ORM and extension constructs.
.. seealso::
:attr:`.QueryableAttribute.info`
:attr:`.SchemaItem.info`
"""
return {}
def setup(self, context, query_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.
"""
def create_row_processor(
self, context, path, mapper, result, adapter, populators
):
"""Produce row processing functions and append to the given
set of populators lists.
"""
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.
This method typically only applies to RelationshipProperty.
"""
return iter(())
def set_parent(self, parent, init):
"""Set the parent mapper that references this MapperProperty.
This method is overridden by some subclasses to perform extra
setup when the mapper is first known.
"""
self.parent = parent
def instrument_class(self, mapper):
"""Hook called by the Mapper to the property to initiate
instrumentation of the class attribute managed by this
MapperProperty.
The MapperProperty here will typically call out to the
attributes module to set up an InstrumentedAttribute.
This step is the first of two steps to set up an InstrumentedAttribute,
and is called early in the mapper setup process.
The second step is typically the init_class_attribute step,
called from StrategizedProperty via the post_instrument_class()
hook. This step assigns additional state to the InstrumentedAttribute
(specifically the "impl") which has been determined after the
MapperProperty has determined what kind of persistence
management it needs to do (e.g. scalar, object, collection, etc).
"""
def __init__(self):
self._configure_started = False
self._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.
"""
def post_instrument_class(self, mapper):
"""Perform instrumentation adjustments that need to occur
after init() has completed.
The given Mapper is the Mapper invoking the operation, which
may not be the same Mapper as self.parent in an inheritance
scenario; however, Mapper will always at least be a sub-mapper of
self.parent.
This method is typically used by StrategizedProperty, which delegates
it to LoaderStrategy.init_class_attribute() to perform final setup
on the class-bound InstrumentedAttribute.
"""
def merge(
self,
session,
source_state,
source_dict,
dest_state,
dest_dict,
load,
_recursive,
_resolve_conflict_map,
):
"""Merge the attribute represented by this ``MapperProperty``
from source to destination object.
"""
def __repr__(self):
return "<%s at 0x%x; %s>" % (
self.__class__.__name__,
id(self),
getattr(self, "key", "no key"),
)
class PropComparator(operators.ColumnOperators):
r"""Defines SQL 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.
.. seealso::
:class:`.ColumnProperty.Comparator`
:class:`.RelationshipProperty.Comparator`
:class:`.CompositeProperty.Comparator`
:class:`.ColumnOperators`
:ref:`types_operators`
:attr:`.TypeEngine.comparator_factory`
"""
__slots__ = "prop", "property", "_parententity", "_adapt_to_entity"
def __init__(self, prop, parentmapper, adapt_to_entity=None):
self.prop = self.property = prop
self._parententity = adapt_to_entity or parentmapper
self._adapt_to_entity = adapt_to_entity
def __clause_element__(self):
raise NotImplementedError("%r" % self)
def _query_clause_element(self):
return self.__clause_element__()
def _bulk_update_tuples(self, value):
return [(self.__clause_element__(), value)]
def adapt_to_entity(self, adapt_to_entity):
"""Return a copy of this PropComparator which will use the given
:class:`.AliasedInsp` to produce corresponding expressions.
"""
return self.__class__(self.prop, self._parententity, adapt_to_entity)
@property
def _parentmapper(self):
"""legacy; this is renamed to _parententity to be
compatible with QueryableAttribute."""
return inspect(self._parententity).mapper
@property
def adapter(self):
"""Produce a callable that adapts column expressions
to suit an aliased version of this comparator.
"""
if self._adapt_to_entity is None:
return None
else:
return self._adapt_to_entity._adapt_element
@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_):
r"""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.
.. seealso::
:ref:`inheritance_of_type`
"""
return self.operate(PropComparator.of_type_op, class_)
def any(self, criterion=None, **kwargs):
r"""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):
r"""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.
The mechanics of StrategizedProperty are used for every Query
invocation for every mapped attribute participating in that Query,
to determine first how the attribute will be rendered in SQL
and secondly how the attribute will retrieve a value from a result
row and apply it to a mapped object. The routines here are very
performance-critical.
"""
__slots__ = (
"_strategies",
"strategy",
"_wildcard_token",
"_default_path_loader_key",
)
strategy_wildcard_key = None
def _memoized_attr__wildcard_token(self):
return (
"%s:%s"
% (self.strategy_wildcard_key, path_registry._WILDCARD_TOKEN),
)
def _memoized_attr__default_path_loader_key(self):
return (
"loader",
(
"%s:%s"
% (self.strategy_wildcard_key, path_registry._DEFAULT_TOKEN),
),
)
def _get_context_loader(self, context, path):
load = None
# use EntityRegistry.__getitem__()->PropRegistry here so
# that the path is stated in terms of our base
search_path = dict.__getitem__(path, self)
# search among: exact match, "attr.*", "default" strategy
# if any.
for path_key in (
search_path._loader_key,
search_path._wildcard_path_loader_key,
search_path._default_path_loader_key,
):
if path_key in context.attributes:
load = context.attributes[path_key]
break
return load
def _get_strategy(self, key):
try:
return self._strategies[key]
except KeyError:
cls = self._strategy_lookup(self, *key)
self._strategies[key] = self._strategies[cls] = strategy = cls(
self, key
)
return strategy
def setup(self, context, query_entity, path, adapter, **kwargs):
loader = self._get_context_loader(context, path)
if loader and loader.strategy:
strat = self._get_strategy(loader.strategy)
else:
strat = self.strategy
strat.setup_query(
context, query_entity, path, loader, adapter, **kwargs
)
def create_row_processor(
self, context, path, mapper, result, adapter, populators
):
loader = self._get_context_loader(context, path)
if loader and loader.strategy:
strat = self._get_strategy(loader.strategy)
else:
strat = self.strategy
strat.create_row_processor(
context, path, loader, mapper, result, adapter, populators
)
def do_init(self):
self._strategies = {}
self.strategy = self._get_strategy(self.strategy_key)
def post_instrument_class(self, mapper):
if (
not self.parent.non_primary
and not mapper.class_manager._attr_has_impl(self.key)
):
self.strategy.init_class_attribute(mapper)
_all_strategies = collections.defaultdict(dict)
@classmethod
def strategy_for(cls, **kw):
def decorate(dec_cls):
# ensure each subclass of the strategy has its
# own _strategy_keys collection
if "_strategy_keys" not in dec_cls.__dict__:
dec_cls._strategy_keys = []
key = tuple(sorted(kw.items()))
cls._all_strategies[cls][key] = dec_cls
dec_cls._strategy_keys.append(key)
return dec_cls
return decorate
@classmethod
def _strategy_lookup(cls, requesting_property, *key):
for prop_cls in cls.__mro__:
if prop_cls in cls._all_strategies:
strategies = cls._all_strategies[prop_cls]
try:
return strategies[key]
except KeyError:
pass
for property_type, strats in cls._all_strategies.items():
if key in strats:
intended_property_type = property_type
actual_strategy = strats[key]
break
else:
intended_property_type = None
actual_strategy = None
raise orm_exc.LoaderStrategyException(
cls,
requesting_property,
intended_property_type,
actual_strategy,
key,
)
class MapperOption(object):
"""Describe a modification to a Query."""
propagate_to_loaders = False
"""if True, indicate this option should be carried along
to "secondary" Query objects produced during lazy loads
or refresh operations.
"""
def process_query(self, query):
"""Apply a modification to the given :class:`.Query`."""
def process_query_conditionally(self, query):
"""same as process_query(), except that this option may not
apply to the given query.
This is typically used during a lazy load or scalar refresh
operation to propagate options stated in the original Query to the
new Query being used for the load. It occurs for those options that
specify propagate_to_loaders=True.
"""
self.process_query(query)
def _generate_cache_key(self, path):
"""Used by the "baked lazy loader" to see if this option can be cached.
The "baked lazy loader" refers to the :class:`.Query` that is
produced during a lazy load operation for a mapped relationship.
It does not yet apply to the "lazy" load operation for deferred
or expired column attributes, however this may change in the future.
This loader generates SQL for a query only once and attempts to cache
it; from that point on, if the SQL has been cached it will no longer
run the :meth:`.Query.options` method of the :class:`.Query`. The
:class:`.MapperOption` object that wishes to participate within a lazy
load operation therefore needs to tell the baked loader that it either
needs to forego this caching, or that it needs to include the state of
the :class:`.MapperOption` itself as part of its cache key, otherwise
SQL or other query state that has been affected by the
:class:`.MapperOption` may be cached in place of a query that does not
include these modifications, or the option may not be invoked at all.
By default, this method returns the value ``False``, which means
the :class:`.BakedQuery` generated by the lazy loader will
not cache the SQL when this :class:`.MapperOption` is present.
This is the safest option and ensures both that the option is
invoked every time, and also that the cache isn't filled up with
an unlimited number of :class:`.Query` objects for an unlimited
number of :class:`.MapperOption` objects.
.. versionchanged:: 1.2.8 the default return value of
:meth:`.MapperOption._generate_cache_key` is False; previously it
was ``None`` indicating "safe to cache, don't include as part of
the cache key"
To enable caching of :class:`.Query` objects within lazy loaders, a
given :class:`.MapperOption` that returns a cache key must return a key
that uniquely identifies the complete state of this option, which will
match any other :class:`.MapperOption` that itself retains the
identical state. This includes path options, flags, etc. It should
be a state that is repeatable and part of a limited set of possible
options.
If the :class:`.MapperOption` does not apply to the given path and
would not affect query results on such a path, it should return None,
indicating the :class:`.Query` is safe to cache for this given
loader path and that this :class:`.MapperOption` need not be
part of the cache key.
"""
return False
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.
For example, simple column attributes will add their represented
column to the list of selected columns, a joined eager loader
may establish join clauses to add 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.
"""
__slots__ = (
"parent_property",
"is_class_level",
"parent",
"key",
"strategy_key",
"strategy_opts",
)
def __init__(self, parent, strategy_key):
self.parent_property = parent
self.is_class_level = False
self.parent = self.parent_property.parent
self.key = self.parent_property.key
self.strategy_key = strategy_key
self.strategy_opts = dict(strategy_key)
def init_class_attribute(self, mapper):
pass
def setup_query(
self, context, query_entity, path, loadopt, adapter, **kwargs
):
"""Establish column and other state for a given QueryContext.
This method fulfills the contract specified by MapperProperty.setup().
StrategizedProperty delegates its setup() method
directly to this method.
"""
def create_row_processor(
self, context, path, loadopt, mapper, result, adapter, populators
):
"""Establish row processing functions for a given QueryContext.
This method fulfills the contract specified by
MapperProperty.create_row_processor().
StrategizedProperty delegates its create_row_processor() method
directly to this method.
"""
def __str__(self):
return str(self.parent_property)
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