sqlalchemy-orm-interfaces-mapperproperty.markdown

title: sqlalchemy.orm.interfaces MapperProperty Example Code category: page slug: sqlalchemy-orm-interfaces-mapperproperty-examples sortorder: 500031083 toc: False sidebartitle: sqlalchemy.orm.interfaces MapperProperty meta: Example code for understanding how to use the MapperProperty class from the sqlalchemy.orm.interfaces module of the SQLAlchemy project.

MapperProperty is a class within the sqlalchemy.orm.interfaces module of the SQLAlchemy project.

PropComparator is another callable from the sqlalchemy.orm.interfaces package with code examples.

Example 1 from sqlalchemy-utils

sqlalchemy-utils (project documentation and PyPI package information) is a code library with various helper functions and new data types that make it easier to use SQLAlchemy when building projects that involve more specific storage requirements such as currency. The wide array of data types includes ranged values and aggregated attributes.

sqlalchemy-utils / sqlalchemy_utils / generic.py

# 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 MapperProperty examples ...



    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):

    def __init__(self, discriminator, id, doc=None):
        super(GenericRelationshipProperty, self).__init__()
        self._discriminator_col = discriminator
        self._id_cols = id
        self._id = None
        self._discriminator = None
        self.doc = doc

        set_creation_order(self)

    def _column_to_property(self, column):
        if isinstance(column, hybrid_property):
            attr_key = column.__name__
            for key, attr in self.parent.all_orm_descriptors.items():
                if key == attr_key:
                    return attr
        else:
            for key, attr in self.parent.attrs.items():
                if isinstance(attr, ColumnProperty):
                    if attr.columns[0].name == column.name:
                        return attr

    def init(self):


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