Hi All,
I am working on a modified version of basic_tree.py. The base
demo simply appends nodes to a parent node. What I would like to do,
is to be able to "prepend" nodes on a parent node, i.e. appending
nodes before other nodes in the tree structure. For example, if a
parent node has this structure:
Parent
|--- Child 1
|--- Child 2
I would like to insert a new item like that:
Parent
|--- NewItem
|--- Child 1
|--- Child 2
So, I have modified the basic demo NodeList class like this:
class NodeList(OrderedDict):
"""subclasses OrderedDict to allow usage as a list-based property."""
def append(self, node):
self[node.name] = node
def insert(self, indx, node):
self[node.name] = node
self.move(node.name, indx)
And then, to prepend an item, I simply do:
node = TreeNode('rootnode')
node.append('Child 1')
node.append('Child 2')
# More actions here...
node.insert('NewItem')
But this newitem gets inserted at the end (like it does when you use
append() ). This happens if I call session.clear(), if I don't do that
the item looks correctly inserted as a first item. I attach a small
demo that shows my problem.
Does anyone know what I am doing wrong or what I have misunderstood?
Thank you for your suggestions.
Andrea.
"Imagination Is The Only Weapon In The War Against Reality."
http://xoomer.virgilio.it/infinity77/
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"""a basic Adjacency List model tree."""
from sqlalchemy import *
from sqlalchemy.util import OrderedDict
class NodeList(OrderedDict):
"""subclasses OrderedDict to allow usage as a list-based property."""
def append(self, node):
self[node.name] = node
def insert(self, indx, node):
self[node.name] = node
self.move(node.name, indx)
def __iter__(self):
return iter(self.values())
class TreeNode(object):
"""a rich Tree class which includes path-based operations"""
def __init__(self, name):
self.children = NodeList()
self.name = name
self.parent = None
self.id = None
self.parent_id = None
def append(self, node):
if isinstance(node, str):
node = TreeNode(node)
node.parent = self
self.children.append(node)
def insert(self, node):
if isinstance(node, str):
node = TreeNode(node)
node.parent = self
self.children.insert(0, node)
def __repr__(self):
return self._getstring(0, False)
def __str__(self):
return self._getstring(0, False)
def _getstring(self, level, expand = False):
s = (' ' * level) + "%s (%s,%s, %d)" % (self.name,
self.id,self.parent_id,id(self)) + '\n'
if expand:
s += ''.join([n._getstring(level+1, True) for n in
self.children.values()])
return s
def print_nodes(self):
return self._getstring(0, True)
def RunBasicTree(clearSession=False):
metadata = BoundMetaData('sqlite:///', echo=False)
trees = Table('treenodes', metadata,
Column('node_id', Integer, Sequence('treenode_id_seq',optional=False),
primary_key=True),
Column('parent_node_id', Integer, ForeignKey('treenodes.node_id'),
nullable=True),
Column('node_name', String(50), nullable=False),
)
mapper(TreeNode, trees, properties=dict(
id=trees.c.node_id,
name=trees.c.node_name,
parent_id=trees.c.parent_node_id,
children=relation(TreeNode, cascade="all", backref=backref("parent",
remote_side=[trees.c.node_id]), collection_class=NodeList),
))
trees.create()
node2 = TreeNode('node2')
node2.append('subnode1')
nodea = TreeNode('rootnode')
nodea.append('node1')
nodea.append(node2)
nodea.append('node3')
nodea.children['node2'].append('subnode2')
session = create_session()
session.save(nodea)
session.flush()
nodea.append('node4')
nodea.children['node4'].append('subnode3')
nodea.children['node4'].append('subnode4')
nodea.children['node4'].children['subnode3'].append('subsubnode1')
del nodea.children['node1']
session.flush()
# ============================ #
# Here I try to insert the node
# ============================ #
nodea.insert("DUMMY!")
session.save(nodea)
session.flush()
nodeid = nodea.id
if clearSession:
print "\n\n\n----------------------------"
print "Clearing session, selecting "
print "tree new where node_id=%d:" % nodeid
print "----------------------------"
# If I don't clear the session, the item looks correctly
# inserted as first child of the root
session.clear()
t = session.query(TreeNode).select(TreeNode.c.id==nodeid)[0]
print "\n----------------------------"
print "Full Tree:"
print "----------------------------"
print t.print_nodes()
# ============================ #
# Modify this variable clearSession to see the different behavior
# ============================ #
clearSession = True
RunBasicTree(clearSession)
