Source code for sqlalchemy.orm.properties

# orm/properties.py
# Copyright (C) 2005-2020 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 individual ORM-
mapped attributes.

"""
from __future__ import absolute_import

from . import attributes
from .interfaces import PropComparator
from .interfaces import StrategizedProperty
from .util import _orm_full_deannotate
from .. import log
from .. import util
from ..sql import expression


__all__ = ["ColumnProperty"]


@log.class_logger
class ColumnProperty(StrategizedProperty):
    """Describes an object attribute that corresponds to a table column.

    Public constructor is the :func:`_orm.column_property` function.

    """

    strategy_wildcard_key = "column"

    __slots__ = (
        "_orig_columns",
        "columns",
        "group",
        "deferred",
        "instrument",
        "comparator_factory",
        "descriptor",
        "extension",
        "active_history",
        "expire_on_flush",
        "info",
        "doc",
        "strategy_key",
        "_creation_order",
        "_is_polymorphic_discriminator",
        "_mapped_by_synonym",
        "_deferred_column_loader",
    )

    @util.deprecated_params(
        extension=(
            "0.7",
            ":class:`.AttributeExtension` is deprecated in favor of the "
            ":class:`.AttributeEvents` listener interface.  The "
            ":paramref:`.column_property.extension` parameter will be "
            "removed in a future release.",
        )
    )
    def __init__(self, *columns, **kwargs):
        r"""Provide a column-level property for use with a mapping.

        Column-based properties can normally be applied to the mapper's
        ``properties`` dictionary using the :class:`_schema.Column`
        element directly.
        Use this function when the given column is not directly present within
        the mapper's selectable; examples include SQL expressions, functions,
        and scalar SELECT queries.

        The :func:`_orm.column_property` function returns an instance of
        :class:`.ColumnProperty`.

        Columns that aren't present in the mapper's selectable won't be
        persisted by the mapper and are effectively "read-only" attributes.

        :param \*cols:
              list of Column objects to be mapped.

        :param active_history=False:
          When ``True``, indicates that the "previous" value for a
          scalar attribute should be loaded when replaced, if not
          already loaded. Normally, history tracking logic for
          simple non-primary-key scalar values only needs to be
          aware of the "new" value in order to perform a flush. This
          flag is available for applications that make use of
          :func:`.attributes.get_history` or :meth:`.Session.is_modified`
          which also need to know
          the "previous" value of the attribute.

        :param comparator_factory: a class which extends
           :class:`.ColumnProperty.Comparator` which provides custom SQL
           clause generation for comparison operations.

        :param group:
            a group name for this property when marked as deferred.

        :param deferred:
              when True, the column property is "deferred", meaning that
              it does not load immediately, and is instead loaded when the
              attribute is first accessed on an instance.  See also
              :func:`~sqlalchemy.orm.deferred`.

        :param doc:
              optional string that will be applied as the doc on the
              class-bound descriptor.

        :param expire_on_flush=True:
            Disable expiry on flush.   A column_property() which refers
            to a SQL expression (and not a single table-bound column)
            is considered to be a "read only" property; populating it
            has no effect on the state of data, and it can only return
            database state.   For this reason a column_property()'s value
            is expired whenever the parent object is involved in a
            flush, that is, has any kind of "dirty" state within a flush.
            Setting this parameter to ``False`` will have the effect of
            leaving any existing value present after the flush proceeds.
            Note however that the :class:`.Session` with default expiration
            settings still expires
            all attributes after a :meth:`.Session.commit` call, however.

        :param info: Optional data dictionary which will be populated into the
            :attr:`.MapperProperty.info` attribute of this object.

        :param extension:
            an :class:`.AttributeExtension` instance, or list of extensions,
            which will be prepended to the list of attribute listeners for the
            resulting descriptor placed on the class.

        .. seealso::

            :ref:`column_property_options` - to map columns while including
            mapping options

            :ref:`mapper_column_property_sql_expressions` - to map SQL
            expressions

        """
        super(ColumnProperty, self).__init__()
        self._orig_columns = [expression._labeled(c) for c in columns]
        self.columns = [
            expression._labeled(_orm_full_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 "info" in kwargs:
            self.info = kwargs.pop("info")

        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)

        self.strategy_key = (
            ("deferred", self.deferred),
            ("instrument", self.instrument),
        )

    @util.dependencies("sqlalchemy.orm.state", "sqlalchemy.orm.strategies")
    def _memoized_attr__deferred_column_loader(self, state, strategies):
        return state.InstanceState._instance_level_callable_processor(
            self.parent.class_manager,
            strategies.LoadDeferredColumns(self.key),
            self.key,
        )

    def __clause_element__(self):
        """Allow the ColumnProperty to work in expression before it is turned
        into an instrumented attribute.
        """

        return self.expression

    @property
    def expression(self):
        """Return the primary column or expression for this ColumnProperty.

        E.g.::


            class File(Base):
                # ...

                name = Column(String(64))
                extension = Column(String(8))
                filename = column_property(name + '.' + extension)
                path = column_property('C:/' + filename.expression)

        .. seealso::

            :ref:`mapper_column_property_sql_expressions_composed`

        """
        return self.columns[0]

    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,
        _resolve_conflict_map,
    ):
        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], no_loader=True
            )

    class Comparator(util.MemoizedSlots, PropComparator):
        """Produce boolean, comparison, and other operators for
        :class:`.ColumnProperty` attributes.

        See the documentation for :class:`.PropComparator` for a brief
        overview.

        .. seealso::

            :class:`.PropComparator`

            :class:`.ColumnOperators`

            :ref:`types_operators`

            :attr:`.TypeEngine.comparator_factory`

        """

        __slots__ = "__clause_element__", "info", "expressions"

        def _memoized_method___clause_element__(self):
            if self.adapter:
                return self.adapter(self.prop.columns[0])
            else:
                # no adapter, so we aren't aliased
                # assert self._parententity is self._parentmapper
                return self.prop.columns[0]._annotate(
                    {
                        "parententity": self._parententity,
                        "parentmapper": self._parententity,
                    }
                )

        def _memoized_attr_info(self):
            """The .info dictionary for this attribute."""

            ce = self.__clause_element__()
            try:
                return ce.info
            except AttributeError:
                return self.prop.info

        def _memoized_attr_expressions(self):
            """The full sequence of columns referenced by this
            attribute, adjusted for any aliasing in progress.

            .. versionadded:: 1.3.17

            """
            if self.adapter:
                return [self.adapter(col) for col in self.prop.columns]
            else:
                # no adapter, so we aren't aliased
                # assert self._parententity is self._parentmapper
                return [
                    col._annotate(
                        {
                            "parententity": self._parententity,
                            "parentmapper": self._parententity,
                            "orm_key": self.prop.key,
                        }
                    )
                    for col in self.prop.columns
                ]

        def _fallback_getattr(self, key):
            """proxy attribute access down to the mapped column.

            this allows user-defined comparison methods to be accessed.
            """
            return getattr(self.__clause_element__(), key)

        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)

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