# orm/interfaces.py # Copyright (C) 2005-2014 the SQLAlchemy authors and contributors # # # 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 from .base import (ONETOMANY, MANYTOONE, MANYTOMANY, EXT_CONTINUE, EXT_STOP, NOT_EXTENSION) from .base import _InspectionAttr, _MappedAttribute from .path_registry import PathRegistry import collections __all__ = ( 'AttributeExtension', 'EXT_CONTINUE', 'EXT_STOP', 'ONETOMANY', 'MANYTOMANY', 'MANYTOONE', 'NOT_EXTENSION', 'LoaderStrategy', 'MapperExtension', 'MapperOption', 'MapperProperty', 'PropComparator', 'SessionExtension', 'StrategizedProperty', ) 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, adapt_to_entity=None): self.prop = self.property = prop self._parentmapper = 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 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._parentmapper, adapt_to_entity) @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 @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 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(*key) self._strategies[key] = self._strategies[ cls] = strategy = cls(self) return strategy def _get_strategy_by_cls(self, cls): return self._get_strategy(cls._strategy_keys[0]) def setup(self, context, 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, entity, path, loader, adapter, **kwargs) def create_row_processor(self, context, path, mapper, row, adapter): loader = self._get_context_loader(context, path) if loader and loader.strategy: strat = self._get_strategy(loader.strategy) else: strat = self.strategy return strat.create_row_processor(context, path, loader, mapper, row, adapter) def do_init(self): self._strategies = {} self.strategy = self._get_strategy_by_cls(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) _strategies = collections.defaultdict(dict) @classmethod def strategy_for(cls, **kw): def decorate(dec_cls): dec_cls._strategy_keys = [] key = tuple(sorted(kw.items())) cls._strategies[cls][key] = dec_cls dec_cls._strategy_keys.append(key) return dec_cls return decorate @classmethod def _strategy_lookup(cls, *key): for prop_cls in cls.__mro__: if prop_cls in cls._strategies: strategies = cls._strategies[prop_cls] try: return strategies[key] except KeyError: pass raise Exception("can't locate strategy for %s %s" % (cls, key)) 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 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, loadopt, adapter, **kwargs): pass def create_row_processor(self, context, path, loadopt, 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)