sqlalchemy.orm attributes Example Code

# generic.py
from collections.abc import Iterable

import six
import sqlalchemy as sa
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import attributes, class_mapper, ColumnProperty
from sqlalchemy.orm.interfaces import MapperProperty, PropComparator
from sqlalchemy.orm.session import _state_session
from sqlalchemy.util import set_creation_order

from .exceptions import ImproperlyConfigured
from .functions import identity


class GenericAttributeImpl(attributes.ScalarAttributeImpl):
    def get(self, state, dict_, passive=attributes.PASSIVE_OFF):
        if self.key in dict_:
            return dict_[self.key]

        session = _state_session(state)
        if session is None:
            return None

        discriminator = self.get_state_discriminator(state)
        target_class = state.class_._decl_class_registry.get(discriminator)

        if target_class is None:
            return None

        id = self.get_state_id(state)


## ... source file abbreviated to get to attributes examples ...


            self.property = prop
            self._parententity = parentmapper

        def __eq__(self, other):
            discriminator = six.text_type(type(other).__name__)
            q = self.property._discriminator_col == discriminator
            other_id = identity(other)
            for index, id in enumerate(self.property._id_cols):
                q &= id == other_id[index]
            return q

        def __ne__(self, other):
            return -(self == other)

        def is_type(self, other):
            mapper = sa.inspect(other)
            class_names = [six.text_type(other.__name__)]
            class_names.extend([
                six.text_type(submapper.class_.__name__)
                for submapper in mapper._inheriting_mappers
            ])

            return self.property._discriminator_col.in_(class_names)

    def instrument_class(self, mapper):
        attributes.register_attribute(
            mapper.class_,
            self.key,
            comparator=self.Comparator(self, mapper),
            parententity=mapper,
            doc=self.doc,
            impl_class=GenericAttributeImpl,
            parent_token=self
        )


def generic_relationship(*args, **kwargs):
    return GenericRelationshipProperty(*args, **kwargs)


        target = session.query(target_class).get(id)

        return target

    def get_state_discriminator(self, state):
        discriminator = self.parent_token.discriminator
        if isinstance(discriminator, hybrid_property):
            return getattr(state.obj(), discriminator.__name__)
        else:
            return state.attrs[discriminator.key].value

    def get_state_id(self, state):
        return tuple(state.attrs[id.key].value for id in self.parent_token.id)

    def set(self, state, dict_, initiator,
            passive=attributes.PASSIVE_OFF,
            check_old=None,
            pop=False):

        dict_[self.key] = initiator

        if initiator is None:
            for id in self.parent_token.id:
                dict_[id.key] = None
            dict_[self.parent_token.discriminator.key] = None
        else:
            class_ = type(initiator)
            mapper = class_mapper(class_)

            pk = mapper.identity_key_from_instance(initiator)[1]

            discriminator = six.text_type(class_.__name__)

            for index, id in enumerate(self.parent_token.id):
                dict_[id.key] = pk[index]
            dict_[self.parent_token.discriminator.key] = discriminator


class GenericRelationshipProperty(MapperProperty):



## ... source file continues with no further attributes examples...