mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-09 02:09:53 -04:00
Mike Bayer
88 lines
2.2 KiB
Python
88 lines
2.2 KiB
Python
"""a directed graph example."""
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from sqlalchemy import MetaData, Table, Column, Integer, ForeignKey, \
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create_engine
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from sqlalchemy.orm import mapper, relationship, sessionmaker
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from sqlalchemy.ext.declarative import declarative_base
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Base = declarative_base()
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class Node(Base):
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__tablename__ = 'node'
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node_id = Column(Integer, primary_key=True)
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def __init__(self, id):
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self.node_id = id
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def add_neighbors(self, *nodes):
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for node in nodes:
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Edge(self, node)
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return self
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def higher_neighbors(self):
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return [x.higher_node for x in self.lower_edges]
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def lower_neighbors(self):
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return [x.lower_node for x in self.higher_edges]
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class Edge(Base):
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__tablename__ = 'edge'
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lower_id = Column(Integer,
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ForeignKey('node.node_id'),
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primary_key=True)
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higher_id = Column(Integer,
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ForeignKey('node.node_id'),
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primary_key=True)
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lower_node = relationship(Node,
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primaryjoin=lower_id==Node.node_id,
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backref='lower_edges')
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higher_node = relationship(Node,
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primaryjoin=higher_id==Node.node_id,
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backref='higher_edges')
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# here we have lower.node_id <= higher.node_id
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def __init__(self, n1, n2):
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if n1.node_id < n2.node_id:
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self.lower_node = n1
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self.higher_node = n2
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else:
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self.lower_node = n2
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self.higher_node = n1
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engine = create_engine('sqlite://', echo=True)
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Base.metadata.create_all(engine)
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session = sessionmaker(engine)()
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# create a directed graph like this:
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# n1 -> n2 -> n5
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# -> n7
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# -> n3 -> n6
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n1 = Node(1)
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n2 = Node(2)
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n3 = Node(3)
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n4 = Node(4)
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n5 = Node(5)
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n6 = Node(6)
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n7 = Node(7)
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n2.add_neighbors(n5, n1)
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n3.add_neighbors(n6)
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n7.add_neighbors(n2)
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n1.add_neighbors(n3)
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session.add_all([n1, n2, n3, n4, n5, n6, n7])
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session.commit()
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assert [x.node_id for x in n3.higher_neighbors()] == [6]
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assert [x.node_id for x in n3.lower_neighbors()] == [1]
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assert [x.node_id for x in n2.lower_neighbors()] == [1]
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assert [x.node_id for x in n2.higher_neighbors()] == [5,7]
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