Release: 1.3.2 | Release Date: April 2, 2019

# SQLAlchemy 1.3 Documentation

# Source code for examples.graphs.directed_graph

    """a directed graph example."""

    from sqlalchemy import Column
    from sqlalchemy import create_engine
    from sqlalchemy import ForeignKey
    from sqlalchemy import Integer
    from sqlalchemy.ext.declarative import declarative_base
    from sqlalchemy.orm import relationship
    from sqlalchemy.orm import sessionmaker

    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]