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POHow can I pass specific attributes across several objects using SQLAlchemies association_proxy?
 

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  1. POHow can I pass specific attributes across several objects using SQLAlchemies association_proxy?
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    <p>I have two types of objects:</p> <ul> <li>divers <code>ValueObjects</code> that inherit from <code>BaseValueObject</code>, and</li> <li><code>Addendum</code>-objects that carry annotations.</li> </ul> <p><code>Addendum</code> has specific annotations (attributes: <code>name</code>, <code>description</code>, <code>flag</code>) and general annotations (<code>(badgetype, badgevalue)</code>) where the <code>badgevalue</code> is stored in a <code>Badge</code>-object and the <code>badgetype in an</code>AddendumBadgeMap`-object.</p> <p>Now, I would like to access</p> <ul> <li><code>name</code>, <code>description</code>, and <code>flag</code> as attributes from <code>ValueOjects</code> and</li> <li><code>Badges</code> directly from <code>ValueOjects</code> as a dictionary.</li> </ul> <p>Here is an example implementation:</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 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} 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) class Badge(Base): __tablename__ = 'badges' id = sa.Column (sa.Integer, primary_key=True) value = sa.Column (sa.String) 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) ################################### 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") session.add(o1) session.commit() </code></pre> <p>What do I have to add that I can do the following:</p> <pre><code>o1.name = "my_name" # =&gt; `Addendum` will be attached with `name="my_name"` o1.description = "my_description" # =&gt; `descrpiption` of the attached `Addendum` get's changed o1.flag # =&gt; same behavior (in general: there should be max. one `Addendum` per `ValueObject`) o1.bagdes = {"file_origin": "/home/.."} # =&gt; attach to the `Addendum` a `Badge` with `value="/home/.."` and # `AddendumBagdeMap.badge_type="file_origin"` (if `Addendum` does # not exist for this `ValueObject`: create it first) </code></pre>
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