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    <p>One solution would need two parts of implementation:</p> <ol> <li>Implementing a <a href="http://www.sqlalchemy.org/docs/orm/extensions/associationproxy.html#composite-association-proxies" rel="nofollow">composite-association-proxies</a> at <code>Addendum</code></li> <li>Make the new property from (1) <code>Addendum.badges</code> accessible from <code>BaseValueObject</code></li> </ol> <p><strong>Part 1: Implementation of <em>composite-association-proxy</em></strong></p> <p>Add the following properties to <code>Addendum</code>:</p> <pre><code>badges = association_proxy ( 'addendum_badge_maps', 'badge_value', creator=lambda bt, bv: AddendumBadgeMap(badge_type=bt, badge_value=bv) ) </code></pre> <p>and the following to <code>AddendumBadgeMap</code>:</p> <pre><code>addendum = orm.relationship(Addendum, backref=orm.backref( 'addendum_badge_maps', collection_class = attribute_mapped_collection("badge_type"), cascade="all, delete-orphan") ) badge = orm.relationship('Badge', single_parent=True, ) badge_value = association_proxy ('badge', 'value') </code></pre> <p>Now, add a <code>__init__</code>-method to <code>Badge</code>:</p> <pre><code>def __init__(self, value): self.value = value </code></pre> <p>and add the following imports on top:</p> <pre><code>from sqlalchemy.ext.associationproxy import association_proxy from sqlalchemy.orm.collections import attribute_mapped_collection </code></pre> <p><strong>Part 2: Accessing the <code>badge</code>-proxy from <code>BaseValueObjects</code></strong></p> <p>Link <code>Addendum</code>-objects to <code>BaseValueObjects</code> via adding property to <code>Addendum</code>:</p> <pre><code>base_value_object = orm.relationship( "BaseValueObject", backref=orm.backref('addendum', uselist=False) ) </code></pre> <p>In order to access <code>badegs</code> add the following to <code>BaseValueObjects</code>:</p> <pre><code>def add_badge(self, badge_dict={}, **kwargs): if self.addendum is None: self.addendum = Addendum() badge_dict.update(kwargs) self.addendum.badges = badge_dict _name = association_proxy('addendum', 'name', creator=lambda name: Addendum( name=name, description='', flag=False)) _description = association_proxy('addendum', 'description', creator=lambda description: Addendum( name='', description=description, flag=False)) _flag = association_proxy('addendum', 'flag', creator=lambda flag: Addendum( name='', description='', flag=flag)) @property def badges(self): try: return self.addendum.badges except AttributeError: "In case that there is no ``Addendum`` specified, yet." return None @badges.setter def badges(self, value): self.add_badge(value) @property def name(self): try: return self._name except AttributeError: "In case that there is no ``Addendum`` specified, yet." return "" @name.setter def name(self, value): self._name = value @property def description(self): try: return self._description except AttributeError: "In case that there is no ``Addendum`` specified, yet." return "" @description.setter def description(self, value): self._description = value @property def flag(self): try: return self._flag except AttributeError: "In case that there is no ``Addendum`` specified, yet." return "" @flag.setter def flag(self, value): self._flag = value </code></pre> <p><strong>The complete code</strong></p> <pre><code>import sqlalchemy as sa import sqlalchemy.orm as orm from sqlalchemy.orm import scoped_session, sessionmaker from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.ext.associationproxy import association_proxy from sqlalchemy.orm.collections import attribute_mapped_collection DBSession = scoped_session(sessionmaker()) Base = declarative_base () ###### ValueObjects: ########## class BaseValueObject(Base): __tablename__ = 'value_objects' id = sa.Column(sa.Integer, primary_key=True) vo_type = sa.Column (sa.String, nullable=False) __mapper_args__ = {'polymorphic_on': vo_type} # Define Badge-Access: def add_badge(self, badge_dict={}, **kwargs): if self.addendum is None: self.addendum = Addendum() badge_dict.update(kwargs) self.addendum.badges = badge_dict _name = association_proxy('addendum', 'name', creator=lambda name: Addendum( name=name, description='', flag=False)) _description = association_proxy('addendum', 'description', creator=lambda description: Addendum( name='', description=description, flag=False)) _flag = association_proxy('addendum', 'flag', creator=lambda flag: Addendum( name='', description='', flag=flag)) @property def badges(self): try: return self.addendum.badges except AttributeError: "In case that there is no ``Addendum`` specified, yet." return None @badges.setter def badges(self, value): self.add_badge(value) @property def name(self): try: return self._name except AttributeError: "In case that there is no ``Addendum`` specified, yet." return "" @name.setter def name(self, value): self._name = value @property def description(self): try: return self._description except AttributeError: "In case that there is no ``Addendum`` specified, yet." return "" @description.setter def description(self, value): self._description = value @property def flag(self): try: return self._flag except AttributeError: "In case that there is no ``Addendum`` specified, yet." return "" @flag.setter def flag(self, value): self._flag = value class ObjectOne(BaseValueObject): __tablename__ = 'objects_one' __mapper_args__ = {'polymorphic_identity': 'ObjectOne'} id = sa.Column(sa.ForeignKey('value_objects.id'), primary_key=True) any_attribute = sa.Column(sa.String) class ObjectTwo(BaseValueObject): __tablename__ = 'objects_two' __mapper_args__ = {'polymorphic_identity': 'ObjectTwo'} id = sa.Column(sa.ForeignKey('value_objects.id'), primary_key=True) any_attribute = sa.Column(sa.String) ############################### ##### Addendum and Bagde ########## class Addendum(Base): __tablename__ = 'addenda' __table_args__ = ( sa.UniqueConstraint('name', 'id'), {} ) id = sa.Column (sa.Integer, primary_key=True) name = sa.Column (sa.String, nullable=False, default='') description = sa.Column (sa.String, nullable=False, default='') flag = sa.Column ( sa.Boolean, nullable=False, default=False) value_object_id = sa.Column ( sa.ForeignKey ('value_objects.id'), unique=True) # Properties: base_value_object = orm.relationship( "BaseValueObject", backref=orm.backref('addendum', uselist=False) ) badges = association_proxy ( 'addendum_badge_maps', 'badge_value', creator=lambda bt, bv: AddendumBadgeMap(badge_type=bt, badge_value=bv) ) class Badge(Base): __tablename__ = 'badges' id = sa.Column (sa.Integer, primary_key=True) value = sa.Column (sa.String) def __init__(self, value): self.value = value class AddendumBadgeMap(Base): __tablename__ = 'addendum_badge_maps' __table_args__ = ( sa.PrimaryKeyConstraint('id'), sa.UniqueConstraint('badge_id', 'badge_type'), {} ) id = sa.Column('id', sa.Integer) addendum_id = sa.Column(sa.ForeignKey('addenda.id'), nullable=False) badge_id = sa.Column(sa.ForeignKey('badges.id'), nullable=False) badge_type = sa.Column (sa.String) #Properties: addendum = orm.relationship(Addendum, backref=orm.backref( 'addendum_badge_maps', collection_class = attribute_mapped_collection("badge_type"), cascade="all, delete-orphan") ) badge = orm.relationship('Badge', single_parent=True, ) badge_value = association_proxy ('badge', 'value') ################################### if __name__ == '__main__': engine = sa.create_engine('sqlite:///:memory:', echo=True) DBSession.configure(bind=engine) Base.metadata.create_all(engine) session = DBSession() o1 = ObjectOne(any_attribute="test1") o1.name = "First Object" session.add(o1) session.commit() o1.badges = {'first name': 'Max'} o1.badges['last name'] = 'Mueller' session.commit() print o1.name print o1.description print o1.flag print o1.any_attribute print o1.badges </code></pre>
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    1. POHow can I pass specific attributes across several objects using SQLAlchemies association_proxy?
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    1. USPhilipp der Rautenberg
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