349 lines
12 KiB
Python
349 lines
12 KiB
Python
# orm/properties.py
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# Copyright (C) 2005-2020 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: http://www.opensource.org/licenses/mit-license.php
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"""MapperProperty implementations.
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This is a private module which defines the behavior of individual ORM-
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mapped attributes.
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"""
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from __future__ import absolute_import
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from . import attributes
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from .interfaces import PropComparator
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from .interfaces import StrategizedProperty
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from .util import _orm_full_deannotate
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from .. import log
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from .. import util
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from ..sql import expression
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__all__ = ["ColumnProperty"]
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@log.class_logger
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class ColumnProperty(StrategizedProperty):
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"""Describes an object attribute that corresponds to a table column.
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Public constructor is the :func:`.orm.column_property` function.
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"""
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strategy_wildcard_key = "column"
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__slots__ = (
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"_orig_columns",
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"columns",
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"group",
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"deferred",
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"instrument",
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"comparator_factory",
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"descriptor",
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"extension",
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"active_history",
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"expire_on_flush",
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"info",
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"doc",
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"strategy_key",
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"_creation_order",
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"_is_polymorphic_discriminator",
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"_mapped_by_synonym",
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"_deferred_column_loader",
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)
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@util.deprecated_params(
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extension=(
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"0.7",
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":class:`.AttributeExtension` is deprecated in favor of the "
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":class:`.AttributeEvents` listener interface. The "
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":paramref:`.column_property.extension` parameter will be "
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"removed in a future release.",
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)
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)
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def __init__(self, *columns, **kwargs):
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r"""Provide a column-level property for use with a mapping.
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Column-based properties can normally be applied to the mapper's
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``properties`` dictionary using the :class:`.Column` element directly.
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Use this function when the given column is not directly present within
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the mapper's selectable; examples include SQL expressions, functions,
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and scalar SELECT queries.
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The :func:`.orm.column_property` function returns an instance of
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:class:`.ColumnProperty`.
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Columns that aren't present in the mapper's selectable won't be
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persisted by the mapper and are effectively "read-only" attributes.
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:param \*cols:
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list of Column objects to be mapped.
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:param active_history=False:
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When ``True``, indicates that the "previous" value for a
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scalar attribute should be loaded when replaced, if not
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already loaded. Normally, history tracking logic for
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simple non-primary-key scalar values only needs to be
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aware of the "new" value in order to perform a flush. This
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flag is available for applications that make use of
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:func:`.attributes.get_history` or :meth:`.Session.is_modified`
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which also need to know
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the "previous" value of the attribute.
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:param comparator_factory: a class which extends
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:class:`.ColumnProperty.Comparator` which provides custom SQL
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clause generation for comparison operations.
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:param group:
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a group name for this property when marked as deferred.
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:param deferred:
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when True, the column property is "deferred", meaning that
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it does not load immediately, and is instead loaded when the
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attribute is first accessed on an instance. See also
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:func:`~sqlalchemy.orm.deferred`.
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:param doc:
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optional string that will be applied as the doc on the
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class-bound descriptor.
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:param expire_on_flush=True:
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Disable expiry on flush. A column_property() which refers
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to a SQL expression (and not a single table-bound column)
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is considered to be a "read only" property; populating it
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has no effect on the state of data, and it can only return
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database state. For this reason a column_property()'s value
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is expired whenever the parent object is involved in a
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flush, that is, has any kind of "dirty" state within a flush.
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Setting this parameter to ``False`` will have the effect of
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leaving any existing value present after the flush proceeds.
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Note however that the :class:`.Session` with default expiration
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settings still expires
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all attributes after a :meth:`.Session.commit` call, however.
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:param info: Optional data dictionary which will be populated into the
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:attr:`.MapperProperty.info` attribute of this object.
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:param extension:
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an :class:`.AttributeExtension` instance, or list of extensions,
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which will be prepended to the list of attribute listeners for the
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resulting descriptor placed on the class.
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.. seealso::
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:ref:`column_property_options` - to map columns while including
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mapping options
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:ref:`mapper_column_property_sql_expressions` - to map SQL
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expressions
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"""
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super(ColumnProperty, self).__init__()
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self._orig_columns = [expression._labeled(c) for c in columns]
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self.columns = [
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expression._labeled(_orm_full_deannotate(c)) for c in columns
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]
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self.group = kwargs.pop("group", None)
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self.deferred = kwargs.pop("deferred", False)
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self.instrument = kwargs.pop("_instrument", True)
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self.comparator_factory = kwargs.pop(
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"comparator_factory", self.__class__.Comparator
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)
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self.descriptor = kwargs.pop("descriptor", None)
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self.extension = kwargs.pop("extension", None)
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self.active_history = kwargs.pop("active_history", False)
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self.expire_on_flush = kwargs.pop("expire_on_flush", True)
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if "info" in kwargs:
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self.info = kwargs.pop("info")
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if "doc" in kwargs:
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self.doc = kwargs.pop("doc")
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else:
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for col in reversed(self.columns):
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doc = getattr(col, "doc", None)
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if doc is not None:
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self.doc = doc
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break
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else:
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self.doc = None
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if kwargs:
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raise TypeError(
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"%s received unexpected keyword argument(s): %s"
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% (self.__class__.__name__, ", ".join(sorted(kwargs.keys())))
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)
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util.set_creation_order(self)
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self.strategy_key = (
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("deferred", self.deferred),
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("instrument", self.instrument),
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)
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@util.dependencies("sqlalchemy.orm.state", "sqlalchemy.orm.strategies")
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def _memoized_attr__deferred_column_loader(self, state, strategies):
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return state.InstanceState._instance_level_callable_processor(
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self.parent.class_manager,
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strategies.LoadDeferredColumns(self.key),
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self.key,
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)
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def __clause_element__(self):
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"""Allow the ColumnProperty to work in expression before it is turned
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into an instrumented attribute.
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"""
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return self.expression
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@property
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def expression(self):
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"""Return the primary column or expression for this ColumnProperty.
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E.g.::
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class File(Base):
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# ...
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name = Column(String(64))
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extension = Column(String(8))
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filename = column_property(name + '.' + extension)
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path = column_property('C:/' + filename.expression)
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.. seealso::
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:ref:`mapper_column_property_sql_expressions_composed`
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"""
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return self.columns[0]
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def instrument_class(self, mapper):
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if not self.instrument:
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return
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attributes.register_descriptor(
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mapper.class_,
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self.key,
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comparator=self.comparator_factory(self, mapper),
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parententity=mapper,
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doc=self.doc,
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)
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def do_init(self):
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super(ColumnProperty, self).do_init()
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if len(self.columns) > 1 and set(self.parent.primary_key).issuperset(
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self.columns
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):
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util.warn(
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(
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"On mapper %s, primary key column '%s' is being combined "
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"with distinct primary key column '%s' in attribute '%s'. "
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"Use explicit properties to give each column its own "
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"mapped attribute name."
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)
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% (self.parent, self.columns[1], self.columns[0], self.key)
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)
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def copy(self):
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return ColumnProperty(
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deferred=self.deferred,
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group=self.group,
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active_history=self.active_history,
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*self.columns
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)
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def _getcommitted(
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self, state, dict_, column, passive=attributes.PASSIVE_OFF
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):
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return state.get_impl(self.key).get_committed_value(
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state, dict_, passive=passive
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)
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def merge(
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self,
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session,
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source_state,
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source_dict,
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dest_state,
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dest_dict,
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load,
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_recursive,
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_resolve_conflict_map,
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):
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if not self.instrument:
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return
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elif self.key in source_dict:
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value = source_dict[self.key]
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if not load:
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dest_dict[self.key] = value
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else:
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impl = dest_state.get_impl(self.key)
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impl.set(dest_state, dest_dict, value, None)
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elif dest_state.has_identity and self.key not in dest_dict:
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dest_state._expire_attributes(
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dest_dict, [self.key], no_loader=True
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)
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class Comparator(util.MemoizedSlots, PropComparator):
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"""Produce boolean, comparison, and other operators for
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:class:`.ColumnProperty` attributes.
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See the documentation for :class:`.PropComparator` for a brief
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overview.
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.. seealso::
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:class:`.PropComparator`
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:class:`.ColumnOperators`
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:ref:`types_operators`
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:attr:`.TypeEngine.comparator_factory`
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"""
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__slots__ = "__clause_element__", "info"
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def _memoized_method___clause_element__(self):
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if self.adapter:
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return self.adapter(self.prop.columns[0])
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else:
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# no adapter, so we aren't aliased
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# assert self._parententity is self._parentmapper
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return self.prop.columns[0]._annotate(
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{
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"parententity": self._parententity,
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"parentmapper": self._parententity,
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}
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)
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def _memoized_attr_info(self):
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ce = self.__clause_element__()
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try:
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return ce.info
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except AttributeError:
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return self.prop.info
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def _fallback_getattr(self, key):
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"""proxy attribute access down to the mapped column.
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this allows user-defined comparison methods to be accessed.
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"""
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return getattr(self.__clause_element__(), key)
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def operate(self, op, *other, **kwargs):
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return op(self.__clause_element__(), *other, **kwargs)
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def reverse_operate(self, op, other, **kwargs):
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col = self.__clause_element__()
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return op(col._bind_param(op, other), col, **kwargs)
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def __str__(self):
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return str(self.parent.class_.__name__) + "." + self.key
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