Source code for examples.adjacency_list.adjacency_list
from sqlalchemy import Column, ForeignKey, Integer, String, create_engine
from sqlalchemy.orm import Session, relationship, backref,\
joinedload_all
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm.collections import attribute_mapped_collection
Base = declarative_base()
class TreeNode(Base):
__tablename__ = 'tree'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey(id))
name = Column(String(50), nullable=False)
children = relationship("TreeNode",
# cascade deletions
cascade="all, delete-orphan",
# many to one + adjacency list - remote_side
# is required to reference the 'remote'
# column in the join condition.
backref=backref("parent", remote_side=id),
# children will be represented as a dictionary
# on the "name" attribute.
collection_class=attribute_mapped_collection('name'),
)
def __init__(self, name, parent=None):
self.name = name
self.parent = parent
def __repr__(self):
return "TreeNode(name=%r, id=%r, parent_id=%r)" % (
self.name,
self.id,
self.parent_id
)
def dump(self, _indent=0):
return " " * _indent + repr(self) + \
"\n" + \
"".join([
c.dump(_indent + 1)
for c in self.children.values()]
)
if __name__ == '__main__':
engine = create_engine('sqlite://', echo=True)
def msg(msg, *args):
msg = msg % args
print("\n\n\n" + "-" * len(msg.split("\n")[0]))
print(msg)
print("-" * len(msg.split("\n")[0]))
msg("Creating Tree Table:")
Base.metadata.create_all(engine)
session = Session(engine)
node = TreeNode('rootnode')
TreeNode('node1', parent=node)
TreeNode('node3', parent=node)
node2 = TreeNode('node2')
TreeNode('subnode1', parent=node2)
node.children['node2'] = node2
TreeNode('subnode2', parent=node.children['node2'])
msg("Created new tree structure:\n%s", node.dump())
msg("flush + commit:")
session.add(node)
session.commit()
msg("Tree After Save:\n %s", node.dump())
TreeNode('node4', parent=node)
TreeNode('subnode3', parent=node.children['node4'])
TreeNode('subnode4', parent=node.children['node4'])
TreeNode('subsubnode1', parent=node.children['node4'].children['subnode3'])
# remove node1 from the parent, which will trigger a delete
# via the delete-orphan cascade.
del node.children['node1']
msg("Removed node1. flush + commit:")
session.commit()
msg("Tree after save:\n %s", node.dump())
msg("Emptying out the session entirely, "
"selecting tree on root, using eager loading to join four levels deep.")
session.expunge_all()
node = session.query(TreeNode).\
options(joinedload_all("children", "children",
"children", "children")).\
filter(TreeNode.name == "rootnode").\
first()
msg("Full Tree:\n%s", node.dump())
msg("Marking root node as deleted, flush + commit:")
session.delete(node)
session.commit()