I read a little bit of discussion on mixin classes in the archives, but
nothing was finalized.
My use case sounds something like this:
- I have objects I want to track last modified date and deleted attribute on
- Code will be exactly the same between totally disparate classes
Having one class Modifiable to do the modified date stuff works fine.
Having one class Deletable also works fine.
If something is Modifiable, it's a subclass of Modifiable. I'm know this
isn't how sqlobject.inheritance is supposed to work, but I'm pretty sure
this is how SQLObject inheritance is supposed to work (line 273 of main.py).
The problem is when I want something to be Modifiable and Deletable. The
new class only gets the columns from the first parent and ignores the
second one. I think this is also because of line 273 from main.py, but I
couldn't figure out how to make it take the columnDefinitions from all
parents.
Instead I wrote a small ugly patch to do something like _inheritable does.
It uses _mixIn and will add all columns from mixed in parent classes to
children.
There are lots of limitations and side-effects:
- I don't know how it fits with sqlobject.inheritance.
- It doesn't mixin joins or indexes.
- The first parent's columns are still included by SQLObject inheritance,
which I'm sure will have weird side-effects later on.
I figured I'd send the patch just to get some discussion going about mixins
though. If they're not the best solution for this case, then feel free to
say that as well.
Jason
--
If you understand, things are just as they are. If you do not understand,
things are just as they are.
Index: sqlobject/main.py
===================================================================
--- sqlobject/main.py (revision 1232)
+++ sqlobject/main.py (working copy)
@@ -738,6 +738,14 @@
cls.sqlmeta.columnDefinitions['childName'] = col.StringCol(
name='childName', default=None)
+ for superclass in cls.__bases__:
+ if hasattr(superclass, '_mixIn') and superclass._mixIn:
+ implicitMixInColumns = _collectAttributes(
+ superclass, superclass.sqlmeta.columnDefinitions, col.Col, set_name=True, sort=True, delete=False)
+ for i in implicitMixInColumns:
+ if i not in cls.sqlmeta.columnDefinitions.values():
+ implicitColumns.append(i)
+
######################################################
# Set some attributes to their defaults, if necessary.
# First we get the connection:
