mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-06-01 05:18:44 -04:00
Mike Bayer
c6bceb7775
- converted all eager to joined in examples - fixed beaker/advanced.py to reference RelationshipCache
134 lines
4.0 KiB
Python
134 lines
4.0 KiB
Python
from sqlalchemy import MetaData, Table, Column, Sequence, ForeignKey,\
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Integer, String, create_engine
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from sqlalchemy.orm import sessionmaker, mapper, relationship, backref,\
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joinedload_all
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from sqlalchemy.orm.collections import attribute_mapped_collection
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metadata = MetaData()
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tree_table = Table('tree', metadata,
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Column('id', Integer, primary_key=True),
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Column('parent_id', Integer, ForeignKey('tree.id')),
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Column('name', String(50), nullable=False)
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)
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class TreeNode(object):
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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 append(self, nodename):
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self.children[nodename] = TreeNode(nodename, parent=self)
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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_tree(node, indent=0):
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return " " * indent + repr(node) + \
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"\n" + \
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"".join([
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dump_tree(c, indent +1)
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for c in node.children.values()]
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)
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mapper(TreeNode, tree_table, properties={
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'children': relationship(TreeNode,
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# cascade deletions
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cascade="all",
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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=tree_table.c.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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})
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if __name__ == '__main__':
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engine = create_engine('sqlite://', echo=True)
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def msg(msg):
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print "\n\n\n" + "-" * len(msg)
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print msg
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print "-" * len(msg)
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msg("Creating Tree Table:")
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metadata.create_all(engine)
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# session. using expire_on_commit=False
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# so that the session's contents are not expired
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# after each transaction commit.
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session = sessionmaker(engine, expire_on_commit=False)()
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node = TreeNode('rootnode')
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node.append('node1')
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node.append('node3')
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node2 = TreeNode('node2')
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node2.append('subnode1')
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node.children['node2'] = node2
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node.children['node2'].append('subnode2')
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msg("Created new tree structure:")
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print dump_tree(node)
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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:")
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print dump_tree(node)
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node.append('node4')
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node.children['node4'].append('subnode3')
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node.children['node4'].append('subnode4')
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node.children['node4'].children['subnode3'].append('subsubnode1')
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# mark node1 as deleted and remove
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session.delete(node.children['node1'])
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msg("Removed node1. flush + commit:")
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session.commit()
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print "\n\n\n----------------------------"
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print "Tree After Save:"
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print "----------------------------"
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# expire the "children" collection so that
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# it reflects the deletion of "node1".
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session.expire(node, ['children'])
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print dump_tree(node)
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msg("Emptying out the session entirely, "
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"selecting tree on root, using 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:")
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print dump_tree(node)
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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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