MAPluggableAccessor and block equality

[Norbert Hartl]

On Fri, 2009-06-26 at 12:52 +0200, Lukas Renggli wrote:
> >> > I'm toying around with MAPluggableAccessor. While I really like
> >> > to introduce some kind of delegated descriptions it doesn't
> >> > work that easy. I'm not really familiar with caching of the
> >> > magritte descriptions. My problem is that I'm operating on
> >> > a MAContainerComponent using childAt: .
> >>
> >> I don't have such a method.
> >>
> > Really? If this since ages and it seems to be your code :)
> >
> > MAContainerComponent>>childAt: aDescription
> >   ^ children at: aDescription ifAbsent: [ nil ]
> 
> Ahh, I thought you refereed to MAContainerDescription. I have
> #childAt: in MAContainerComponent too.
> 
> What you could try is to replace the Dictionary with an
> IdentityDictionary in #buildChildren of MAContainerComponent. I am not
> quite sure about all the consequences, but I guess it should solve
> your problem.
> 
Ok, I test it at least.

> >> I don't understand the above part.
> >>
> > I was just wondering if I try to use the MAPluggableAccessor the
> > wrong way and hence facing problems. I can do
> >
> > accessor
> >   ^ accessor ifNil: [
> >      accessor := (MAPluggableAccessor
> >         read: [:model|]
> >         write: [:model :object| ]) ]
> >
> > and then
> >
> > descriptionThings
> >   ^ MAToManyRelationDescription
> >      accessor: self accessor
> >      label: 'Things'
> >      priority: 10
> >
> > This way I get it running but I don't like it much. I don't know exactly
> > what MANamedBuilder is caching. I just thought it might solve the
> > problem by caching the instances.
> 
> Why don't quite understand what you are trying to do? If you don't use
> the accessor just don't assign one.
> 
I must be more careful about how to do example code :) At the end the
blocks are of course not empty. Storing the accessor in an instance
variable gives me the identical accessor object with identical blocks.
This way the childAt: call succeeds.

The whole problem deals with tags. Until now I had several objects that
should be taggable. But as the code grew there were other things those
objects could have: comments, scores, etc.

Trying to solve this by inheritance is not possible for me. My idea now
is to treat tags more as meta data: The objects don't contain the data
anymore. At the moment I have any taggable object WHChallenge to that
I add

WHChallenge class>>descriptionTags
   ^ WHTag tagsDescription

WHTag class>>tagsDescription
   ^ (MAToManyRelationDescription
      accessor: (MAPluggableAccessor 
         read: [:model|self tagsFor: model] 
         write: [:model :tags| self storeTags: tags for: model])
      label: 'Tags'
      priority: 40
   )
   classes: {WHTag};
   reference: WHTag description;
   componentClass: WHTagSelectComponent;
   yourself

The WHTag classes holds all the tag instances. If this approach works
out I would try to solve this even more generic so that I can have a
common code base for this meta-data/annotation kind of things. All 
other cases for comments, scores etc. should then be fairly easy

Norbert