[SQLObject] Re: SQLObject mixins

[Randall S. <ra...@tn...>]

Jason Chu wrote:
> 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
> 
> 
> 
> ------------------------------------------------------------------------
> 
> 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:

I am dealing with the same issue.  What did you end up doing?

Randall