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POSetting delete-orphan on SQLAlchemy relationship causes AssertionError: This AttributeImpl is not configured to track parents
 

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  1. POSetting delete-orphan on SQLAlchemy relationship causes AssertionError: This AttributeImpl is not configured to track parents
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    <p>this is my Flask-SQLAlchemy Declarative code:</p> <pre><code>from sqlalchemy.ext.associationproxy import association_proxy from my_flask_project import db tagging = db.Table('tagging', db.Column('tag_id', db.Integer, db.ForeignKey('tag.id', ondelete='cascade'), primary_key=True), db.Column('role_id', db.Integer, db.ForeignKey('role.id', ondelete='cascade'), primary_key=True) ) class Tag(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(100), unique=True, nullable=False) def __init__(self, name=None): self.name = name @classmethod def delete_orphans(cls): for tag in Tag.query.outerjoin(tagging).filter(tagging.c.role_id == None): db.session.delete(tag) class Role(db.Model): id = db.Column(db.Integer, primary_key=True) user_id = db.Column(db.Integer, db.ForeignKey('user.id', ondelete='cascade')) user = db.relationship('User', backref=db.backref('roles', cascade='all', lazy='dynamic')) ... tags = db.relationship('Tag', secondary=tagging, cascade='all', backref=db.backref('roles', cascade='all')) tag_names = association_proxy('tags', 'name') __table_args__ = ( db.UniqueConstraint('user_id', 'check_id'), ) </code></pre> <p>Basically, it's many-to-many tagging with Declarative. When deleting some entries from tagging, I want SQLAlchemy to tidy up the orphans. As I found out in docs, to turn on this feature, I should do this:</p> <pre><code>class Role(db.Model): ... tags = db.relationship('Tag', secondary=tagging, cascade='all,delete-orphan', backref=db.backref('roles', cascade='all')) ... </code></pre> <p>However, such setting leads to <strong>AssertionError: This AttributeImpl is not configured to track parents.</strong> I googled it and found nothing except of the opensourced code of SQLAlchemy. Therefore, I created the classmethod <code>Tag.delete_orphans()</code> (it's in the code above) to call it every time I think some orphans could occure, but that doesn't seem to be very elegant.</p> <p>Any ideas or explanations why my setting with <code>delete-orphan</code> doesn't work?</p>
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