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|
"""
A class for storing a tree graph. Primarily used for filter constructs in the
ORM.
"""
import copy
from django.utils.hashable import make_hashable
class Node:
"""
A single internal node in the tree graph. A Node should be viewed as a
connection (the root) with the children being either leaf nodes or other
Node instances.
"""
# Standard connector type. Clients usually won't use this at all and
# subclasses will usually override the value.
default = "DEFAULT"
def __init__(self, children=None, connector=None, negated=False):
"""Construct a new Node. If no connector is given, use the default."""
self.children = children[:] if children else []
self.connector = connector or self.default
self.negated = negated
@classmethod
def create(cls, children=None, connector=None, negated=False):
"""
Create a new instance using Node() instead of __init__() as some
subclasses, e.g. django.db.models.query_utils.Q, may implement a custom
__init__() with a signature that conflicts with the one defined in
Node.__init__().
"""
obj = Node(children, connector or cls.default, negated)
obj.__class__ = cls
return obj
def __str__(self):
template = "(NOT (%s: %s))" if self.negated else "(%s: %s)"
return template % (self.connector, ", ".join(str(c) for c in self.children))
def __repr__(self):
return "<%s: %s>" % (self.__class__.__name__, self)
def __copy__(self):
obj = self.create(connector=self.connector, negated=self.negated)
obj.children = self.children # Don't [:] as .__init__() via .create() does.
return obj
copy = __copy__
def __deepcopy__(self, memodict):
obj = self.create(connector=self.connector, negated=self.negated)
obj.children = copy.deepcopy(self.children, memodict)
return obj
def __len__(self):
"""Return the number of children this node has."""
return len(self.children)
def __bool__(self):
"""Return whether or not this node has children."""
return bool(self.children)
def __contains__(self, other):
"""Return True if 'other' is a direct child of this instance."""
return other in self.children
def __eq__(self, other):
return (
self.__class__ == other.__class__
and self.connector == other.connector
and self.negated == other.negated
and self.children == other.children
)
def __hash__(self):
return hash(
(
self.__class__,
self.connector,
self.negated,
*make_hashable(self.children),
)
)
def add(self, data, conn_type):
"""
Combine this tree and the data represented by data using the
connector conn_type. The combine is done by squashing the node other
away if possible.
This tree (self) will never be pushed to a child node of the
combined tree, nor will the connector or negated properties change.
Return a node which can be used in place of data regardless if the
node other got squashed or not.
"""
if self.connector != conn_type:
obj = self.copy()
self.connector = conn_type
self.children = [obj, data]
return data
elif (
isinstance(data, Node)
and not data.negated
and (data.connector == conn_type or len(data) == 1)
):
# We can squash the other node's children directly into this node.
# We are just doing (AB)(CD) == (ABCD) here, with the addition that
# if the length of the other node is 1 the connector doesn't
# matter. However, for the len(self) == 1 case we don't want to do
# the squashing, as it would alter self.connector.
self.children.extend(data.children)
return self
else:
# We could use perhaps additional logic here to see if some
# children could be used for pushdown here.
self.children.append(data)
return data
def negate(self):
"""Negate the sense of the root connector."""
self.negated = not self.negated
|
