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#https://stackoverflow.com/questions/19780178/sqlalchemy-hybrid-expression-with-relationship |
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# 1 association proxy: http://docs.sqlalchemy.org/en/latest/orm/extensions/associationproxy.html |
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from sqlalchemy.ext.associationproxy import association_proxy |
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class NodeVariable(Variable): |
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__tablename__ = 'nodevariables' |
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id = db.Column(db.Integer, db.ForeignKey('variables.id', name='fk_nodevariables_variables_id'), primary_key=True) |
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__mapper_args__ = { |
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'polymorphic_identity': VariableKind.NodeVariable, |
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} |
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node_id = db.Column(db.Integer, db.ForeignKey('nodes.id', name='fk_nodevariables_nodes_id')) |
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node = db.relationship('Node', backref=db.backref('variables', lazy='dynamic')) |
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orchard_id = association_proxy('node', 'orchard_id') |
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# 2 @hybrid_property + set expression in class |
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from sqlalchemy.ext.hybrid import hybrid_property |
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class NodeVariable(Variable): |
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__tablename__ = 'nodevariables' |
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id = db.Column(db.Integer, db.ForeignKey('variables.id', name='fk_nodevariables_variables_id'), primary_key=True) |
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__mapper_args__ = { |
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'polymorphic_identity': VariableKind.NodeVariable, |
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} |
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node_id = db.Column(db.Integer, db.ForeignKey('nodes.id', name='fk_nodevariables_nodes_id')) |
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node = db.relationship('Node', backref=db.backref('variables', lazy='dynamic')) |
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@hybrid_property |
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def orchard_id(self): |
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if self.kind == VariableKind.NodeVariable: |
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return self.node.orchard_id |
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@orchard_id.expression |
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def orchard_id(cls): |
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from .models import Node |
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if cls.__name__ == NodeVariable.__name__: |
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return db.select([Node.orchard_id]).where(cls.node_id == Node.id).as_scalar() |
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# 3 @hybrid_property + set comparator with a transformer of the query |
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# TODO |
