Source code for examples.graphs.directed_graph
"""a directed graph example."""
from sqlalchemy import MetaData, Table, Column, Integer, ForeignKey, \
create_engine
from sqlalchemy.orm import mapper, 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 __init__(self, id):
self.node_id = id
def add_neighbors(self, *nodes):
for node in nodes:
Edge(self, node)
return self
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')
# here we have lower.node_id <= higher.node_id
def __init__(self, n1, n2):
if n1.node_id < n2.node_id:
self.lower_node = n1
self.higher_node = n2
else:
self.lower_node = n2
self.higher_node = n1
engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
# create a directed graph like this:
# n1 -> n2 -> n5
# -> n7
# -> n3 -> n6
n1 = Node(1)
n2 = Node(2)
n3 = Node(3)
n4 = Node(4)
n5 = Node(5)
n6 = Node(6)
n7 = Node(7)
n2.add_neighbors(n5, n1)
n3.add_neighbors(n6)
n7.add_neighbors(n2)
n1.add_neighbors(n3)
session.add_all([n1, n2, n3, n4, n5, n6, n7])
session.commit()
assert [x.node_id for x in n3.higher_neighbors()] == [6]
assert [x.node_id for x in n3.lower_neighbors()] == [1]
assert [x.node_id for x in n2.lower_neighbors()] == [1]
assert [x.node_id for x in n2.higher_neighbors()] == [5,7]