Hi,
I'v been working on an old Oracle bug[1], and realized that a nice way to
solve it would be by overriding some builtin lookups with custom lookups for
Oracle. However, I had some doubts about where to place the code:
On the one hand, I could just add an "as_oracle()" to the builtin lookup
classes. But I felt that would be cheating -- Oracle is in core, but what
would 3rd-party backends do?
So I thought I would implement a custom lookup in the backend, which adds an
"as_oracle", and register that when the backend is loaded. Loic commented that
this is still problematic -- For example, I want to override "contains" on
TextField's, so I would naturally inherit the built-in Contains lookup; but if
a user has two backends which want to override "contains", they will be in
conflict -- only one of them will get to install its handler.
The solution I found was to use dynamic inheritance -- the backend inherits
not the builtin Contains, but the registered lookup for "contains" on
TextField. This way, another backend can also add its own as_vendor() method,
without any of us stepping on each other's feet.
I've posted the initial example of this as a PR[2] for comments.
This is related to some of the discussions about transforms (SQL Functions)
that happened on the mailing list a couple of months ago[3], but the topic of
backend-specific functions was not really the topic there, so I preferred to
open a new discussion.
Have fun,
Shai.
[1] https://code.djangoproject.com/ticket/11580
[2] https://github.com/django/django/pull/3544
[3] https://groups.google.com/d/msg/django-developers/HggiPzwkono/dsnx3BuXpnkJ
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