On Tue, Dec 6, 2011 at 3:33 PM, Daniel Nouri <[email protected]> wrote:
> Here's a little generalization of that GrandparentTransformer that I
> came up with.
>
> class ParentalTransformer(Comparator):
> def __init__(self, expression, level):
> super(ParentalTransformer, self).__init__(expression)
> self.level = level
>
> def operate(self, op, other):
> def transform(query):
> cls = Node
> for i in range(self.level-1):
> cls, prev_cls = aliased(cls), cls
> query = query.filter(cls.id==prev_cls.parent_id)
> return query.filter(op(cls.parent, other))
> return transform
I experimented a little more with the idea of having parametrized
Transformers. Here is one that expects a list of names instead of a
level. At this point, my use is not really related to hybrids
anymore, so I may be using the wrong tools.
class FollowTransformer(Comparator):
def __init__(self, expression, names):
super(FollowTransformer, self).__init__(expression)
self.names = names
def operate(self, op, other):
def transform(query):
cls = self.__clause_element__()
for name in self.names[:-1]:
cls, prev_cls = aliased(cls), cls
query = query.join(cls, getattr(prev_cls, name))
return query.filter(op(getattr(cls, self.names[-1]), other))
return transform
You can see how the transform is really similar to what I had before.
On the Node class I can now use it like so:
class Node(Base):
__tablename__ = 'node'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('node.id'))
parent = relationship("Node", remote_side=id)
@classmethod
def follow(cls, *names):
return FollowTransformer(cls, names)
And it'll allow me to do queries like this:
session.query(Node).with_transformation(Node.follow('parent',
'parent') == grandparent)
session.query(Node).with_transformation(Node.follow('parent',
'id') % 2).filter(Node.id > 5)
which I think looks kinda neat. It reminds of the
DoubleUnderMagicalQuery: http://pastebin.com/31JAxnfZ
--
http://danielnouri.org
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