mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-28 03:26:01 -04:00
Paul Brown
113 lines
3.1 KiB
Python
113 lines
3.1 KiB
Python
from sqlalchemy import Column, ForeignKey, Integer, String, create_engine
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from sqlalchemy.orm import Session, relationship, backref, joinedload_all
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from sqlalchemy.ext.declarative import declarative_base
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from sqlalchemy.orm.collections import attribute_mapped_collection
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Base = declarative_base()
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class TreeNode(Base):
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__tablename__ = 'tree'
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id = Column(Integer, primary_key=True)
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parent_id = Column(Integer, ForeignKey(id))
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name = Column(String(50), nullable=False)
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children = relationship(
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"TreeNode",
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# cascade deletions
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cascade="all, delete-orphan",
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# many to one + adjacency list - remote_side
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# is required to reference the 'remote'
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# column in the join condition.
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backref=backref("parent", remote_side=id),
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# children will be represented as a dictionary
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# on the "name" attribute.
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collection_class=attribute_mapped_collection('name'),
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)
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def __init__(self, name, parent=None):
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self.name = name
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self.parent = parent
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def __repr__(self):
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return "TreeNode(name=%r, id=%r, parent_id=%r)" % (
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self.name,
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self.id,
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self.parent_id
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)
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def dump(self, _indent=0):
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return " " * _indent + repr(self) + \
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"\n" + \
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"".join([
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c.dump(_indent + 1)
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for c in self.children.values()
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])
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if __name__ == '__main__':
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engine = create_engine('sqlite://', echo=True)
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def msg(msg, *args):
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msg = msg % args
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print("\n\n\n" + "-" * len(msg.split("\n")[0]))
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print(msg)
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print("-" * len(msg.split("\n")[0]))
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msg("Creating Tree Table:")
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Base.metadata.create_all(engine)
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session = Session(engine)
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node = TreeNode('rootnode')
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TreeNode('node1', parent=node)
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TreeNode('node3', parent=node)
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node2 = TreeNode('node2')
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TreeNode('subnode1', parent=node2)
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node.children['node2'] = node2
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TreeNode('subnode2', parent=node.children['node2'])
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msg("Created new tree structure:\n%s", node.dump())
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msg("flush + commit:")
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session.add(node)
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session.commit()
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msg("Tree After Save:\n %s", node.dump())
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TreeNode('node4', parent=node)
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TreeNode('subnode3', parent=node.children['node4'])
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TreeNode('subnode4', parent=node.children['node4'])
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TreeNode('subsubnode1', parent=node.children['node4'].children['subnode3'])
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# remove node1 from the parent, which will trigger a delete
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# via the delete-orphan cascade.
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del node.children['node1']
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msg("Removed node1. flush + commit:")
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session.commit()
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msg("Tree after save:\n %s", node.dump())
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msg("Emptying out the session entirely, selecting tree on root, using "
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"eager loading to join four levels deep.")
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session.expunge_all()
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node = session.query(TreeNode).\
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options(joinedload_all("children", "children",
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"children", "children")).\
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filter(TreeNode.name == "rootnode").\
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first()
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msg("Full Tree:\n%s", node.dump())
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msg("Marking root node as deleted, flush + commit:")
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session.delete(node)
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session.commit()
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