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"""a directed graph example."""
from sqlalchemy import Column, Integer, ForeignKey, \
create_engine
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Node(Base):
__tablename__ = 'node'
node_id = Column(Integer, primary_key=True)
def higher_neighbors(self):
return [x.higher_node for x in self.lower_edges]
def lower_neighbors(self):
return [x.lower_node for x in self.higher_edges]
class Edge(Base):
__tablename__ = 'edge'
lower_id = Column(
Integer,
ForeignKey('node.node_id'),
primary_key=True)
higher_id = Column(
Integer,
ForeignKey('node.node_id'),
primary_key=True)
lower_node = relationship(
Node,
primaryjoin=lower_id == Node.node_id,
backref='lower_edges')
higher_node = relationship(
Node,
primaryjoin=higher_id == Node.node_id,
backref='higher_edges')
def __init__(self, n1, n2):
self.lower_node = n1
self.higher_node = n2
engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
# create a directed graph like this:
# n1 -> n2 -> n1
# -> n5
# -> n7
# -> n3 -> n6
n1 = Node()
n2 = Node()
n3 = Node()
n4 = Node()
n5 = Node()
n6 = Node()
n7 = Node()
Edge(n1, n2)
Edge(n1, n3)
Edge(n2, n1)
Edge(n2, n5)
Edge(n2, n7)
Edge(n3, n6)
session.add_all([n1, n2, n3, n4, n5, n6, n7])
session.commit()
assert [x for x in n3.higher_neighbors()] == [n6]
assert [x for x in n3.lower_neighbors()] == [n1]
assert [x for x in n2.lower_neighbors()] == [n1]
assert [x for x in n2.higher_neighbors()] == [n1, n5, n7]
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