mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-31 12:58:45 -04:00
Mike Bayer
216 lines
7.4 KiB
Python
216 lines
7.4 KiB
Python
"""a more advanced example of basic_tree.py. treenodes can now reference their "root" node, and
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introduces a new selection method which selects an entire tree of nodes at once, taking
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advantage of a custom MapperExtension to assemble incoming nodes into their correct structure."""
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from sqlalchemy import *
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from sqlalchemy.orm import *
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from sqlalchemy.orm.collections import attribute_mapped_collection
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engine = create_engine('sqlite:///:memory:', echo=True)
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metadata = MetaData(engine)
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"""create the treenodes table. This is ia basic adjacency list model table.
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One additional column, "root_node_id", references a "root node" row and is used
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in the 'byroot_tree' example."""
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trees = Table('treenodes', metadata,
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Column('node_id', Integer, Sequence('treenode_id_seq',optional=False), primary_key=True),
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Column('parent_node_id', Integer, ForeignKey('treenodes.node_id'), nullable=True),
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Column('root_node_id', Integer, ForeignKey('treenodes.node_id'), nullable=True),
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Column('node_name', String(50), nullable=False),
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Column('data_ident', Integer, ForeignKey('treedata.data_id'))
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)
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treedata = Table(
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"treedata", metadata,
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Column('data_id', Integer, primary_key=True),
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Column('value', String(100), nullable=False)
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)
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class TreeNode(object):
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"""a hierarchical Tree class, which adds the concept of a "root node". The root is
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the topmost node in a tree, or in other words a node whose parent ID is NULL.
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All child nodes that are decendents of a particular root, as well as a root node itself,
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reference this root node. """
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def __init__(self, name):
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self.name = name
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self.root = self
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def _set_root(self, root):
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self.root = root
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for c in self.children.values():
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c._set_root(root)
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def append(self, node):
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if isinstance(node, str):
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node = TreeNode(node)
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node._set_root(self.root)
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self.children.append(node)
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def __repr__(self):
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return self._getstring(0, False)
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def __str__(self):
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return self._getstring(0, False)
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def _getstring(self, level, expand = False):
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s = (' ' * level) + "%s (%s,%s,%s, %d): %s" % (self.name, self.id,self.parent_id,self.root_id, id(self), repr(self.data)) + '\n'
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if expand:
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s += ''.join([n._getstring(level+1, True) for n in self.children.values()])
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return s
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def print_nodes(self):
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return self._getstring(0, True)
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class TreeLoader(MapperExtension):
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def after_insert(self, mapper, connection, instance):
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"""runs after the insert of a new TreeNode row. The primary key of the row is not determined
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until the insert is complete, since most DB's use autoincrementing columns. If this node is
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the root node, we will take the new primary key and update it as the value of the node's
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"root ID" as well, since its root node is itself."""
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if instance.root is instance:
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connection.execute(mapper.mapped_table.update(TreeNode.c.id==instance.id, values=dict(root_node_id=instance.id)))
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instance.root_id = instance.id
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def append_result(self, mapper, selectcontext, row, instance, result, **flags):
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"""runs as results from a SELECT statement are processed, and newly created or already-existing
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instances that correspond to each row are appended to result lists. This method will only
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append root nodes to the result list, and will attach child nodes to their appropriate parent
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node as they arrive from the select results. This allows a SELECT statement which returns
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both root and child nodes in one query to return a list of "roots"."""
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isnew = flags.get('isnew', False)
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if instance.parent_id is None:
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result.append(instance)
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else:
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if isnew or selectcontext.populate_existing:
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parentnode = selectcontext.identity_map[mapper.identity_key(instance.parent_id)]
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parentnode.children.append(instance)
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return False
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class TreeData(object):
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def __init__(self, value=None):
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self.id = None
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self.value = value
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def __repr__(self):
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return "TreeData(%s, %s)" % (repr(self.id), repr(self.value))
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print "\n\n\n----------------------------"
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print "Creating Tree Table:"
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print "----------------------------"
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metadata.create_all()
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# the mapper is created with properties that specify "lazy=None" - this is because we are going
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# to handle our own "eager load" of nodes based on root id
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mapper(TreeNode, trees, properties=dict(
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id=trees.c.node_id,
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name=trees.c.node_name,
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parent_id=trees.c.parent_node_id,
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root_id=trees.c.root_node_id,
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root=relation(TreeNode, primaryjoin=trees.c.root_node_id==trees.c.node_id, remote_side=trees.c.node_id, lazy=None),
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children=relation(TreeNode,
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primaryjoin=trees.c.parent_node_id==trees.c.node_id,
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lazy=None,
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cascade="all",
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collection_class=attribute_mapped_collection('name'),
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backref=backref('parent', primaryjoin=trees.c.parent_node_id==trees.c.node_id, remote_side=trees.c.node_id)
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),
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data=relation(TreeData, cascade="all, delete-orphan", lazy=False)
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), extension = TreeLoader())
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mapper(TreeData, treedata, properties={'id':treedata.c.data_id})
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session = create_session()
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node2 = TreeNode('node2')
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node2.append('subnode1')
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node = TreeNode('rootnode')
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node.append('node1')
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node.append(node2)
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node.append('node3')
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node.children['node3'].data = TreeData('node 3s data')
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node.children['node2'].append('subnode2')
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node.children['node1'].data = TreeData('node 1s data')
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print "\n\n\n----------------------------"
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print "Created new tree structure:"
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print "----------------------------"
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print node.print_nodes()
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print "\n\n\n----------------------------"
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print "flushing:"
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print "----------------------------"
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session.save(node)
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session.flush()
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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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print node.print_nodes()
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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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del node.children['node1']
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print "\n\n\n----------------------------"
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print "Modified the tree"
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print "(added node4, node4/subnode3, node4/subnode4,"
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print "node4/subnode3/subsubnode1, deleted node1):"
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print "----------------------------"
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print node.print_nodes()
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print "\n\n\n----------------------------"
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print "Committing:"
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print "----------------------------"
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session.flush()
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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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print node.print_nodes()
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nodeid = node.id
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print "\n\n\n----------------------------"
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print "Clearing objectstore, selecting "
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print "tree new where root_id=%d:" % nodeid
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print "----------------------------"
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session.clear()
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# load some nodes. we do this based on "root id" which will load an entire sub-tree in one pass.
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# the MapperExtension will assemble the incoming nodes into a tree structure.
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t = session.query(TreeNode).select(TreeNode.c.root_id==nodeid, order_by=[TreeNode.c.id])[0]
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print "\n\n\n----------------------------"
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print "Full Tree:"
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print "----------------------------"
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print t.print_nodes()
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print "\n\n\n----------------------------"
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print "Marking root node as deleted"
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print "and committing:"
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print "----------------------------"
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session.delete(t)
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session.flush()
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