On Dec 26, 2011, at 9:56 AM, k.elkouhen wrote:
> In the example included in the 0.7 documentation, I can't figure out how the
> code backref="left_nodes" works ?
>
> Notably, because I can't find a reference to left_nodes...
left_nodes and right_nodes are essentially equivalent collections:
n1, n2, n3, n4 = Node(label='n1'), Node(label='n2'), Node(label='n3'),
Node(label='n4')
n1.left_nodes = [n2, n3]
n1.right_nodes = [n4]
assert n2.right_nodes == [n1]
assert n3.right_nodes == [n1]
assert n4.left_nodes == [n1]
>
> from sqlalchemy import Integer, ForeignKey, String, Column, Table
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import relationship
>
> Base = declarative_base()
>
> node_to_node = Table("node_to_node", Base.metadata,
> Column("left_node_id", Integer, ForeignKey("node.id"), primary_key=True),
> Column("right_node_id", Integer, ForeignKey("node.id"), primary_key=True)
> )
>
> class Node(Base):
> __tablename__ = 'node'
> id = Column(Integer, primary_key=True)
> label = Column(String)
> right_nodes = relationship("Node",
> secondary=node_to_node,
> primaryjoin=id==node_to_node.c.left_node_id,
> secondaryjoin=id==node_to_node.c.right_node_id,
> backref="left_nodes"
> )
>
>
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