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POFlask SQLAlchemy - Need Help Mapping 3 Classes together
 

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    <p>So I've spent some time on this and keep running around in circles and getting nowhere so I figured I'd come to the experts!</p> <p>Using <code>Flask 0.9</code> and <code>SQLAlchemy 0.7.9</code> I'm attempting to create a Gallery page which has a collection of Gallery's. Each gallery has a collection of sub galleries and each sub gallery has a collection of photo's. My first attempt shown below clearly does not work:</p> <pre><code>class Gallery(db.Model): id = db.Column(db.Integer, primary_key=True) title = db.Column(db.String(64)) subgals = db.relationship('SubGallery', backref='author', lazy='dynamic') def __repr__(self): return '&lt;Gallery - %r&gt;' % (self.title) class SubGallery(db.Model): id = db.Column(db.Integer, primary_key=True) title = db.Column(db.String(64)) photos = db.relationship('Photo', backref='author', lazy='dynamic') gallery_id = db.Column(db.Integer, db.ForeignKey('gallery.id')) def __repr__(self): return '&lt;Gallery - %r&gt;' % (self.title) class Photo(db.Model): id = db.Column(db.Integer, primary_key=True) title = db.Column(db.String(64)) href = db.Column(db.String(128)) subgallery_id = db.Column(db.Integer, db.ForeignKey('subgallery.id')) def __repr__(self): return '&lt;Photo - %r&gt;' % (self.title) </code></pre> <p>and returns this error:</p> <pre><code>sqlalchemy.exc.ArgumentError: Could not determine join condition between parent/child tables on relationship SubGallery.photos. Specify a 'primaryjoin' expression. If 'secondary' is present, 'secondaryjoin' is needed as well. </code></pre> <p>I've been researching alternate relationship configurations but am not 100% sure what I need. My gut tells me I need an <code>Adjacency Relationship</code> but I haven't been able to get very far with it. I attempted a many to many mapping but I haven't seen much material how to map 3 classes together.</p> <p>I REALLY appreciate any input and insight you all have to offer with this and thanks!!</p>
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