Rails - Oct 2005 - Proposal: habtm :join_model option to treat join_table as a real model, enables acts_as_*

Hi people,

In my pursuit of a working acts_as_list for HasAndBelongsTo  
associations I would like to propose the following:

Currently HABTM uses raw sql to create and delete entries in the join  
table. This way the normal AR flow is circumvented, including all the  
normal callback functions (before_create, after_destroy ...)

On the other hand, if you could specify that the join table should be  
treated like a real model (AR object) when doing create and delete on  
it, it would automatically enable a lot of options. Among them,  
working acts_as_* functionality, since most of them are dependent on  
callbacks.

So if the :join_model option would be specified, it would create the  
intermediate join model:

has_and_belongs_to_many :images,
                                         :join_model => true

this would inflect the right model name automatically

has_and_belongs_to_many :images,
                                         :join_model =>
''ImageLookup''

this would be a custom lookup object

Otherwise the normal raw sql version kicks in, since that would be  
the default/fastest implementation.

This would effectively solve among others, this ticket: http:// 
dev.rubyonrails.com/ticket/2025

Unfortunately I''m new to Rails/Ruby, but maybe someone could shed a  
light on this.

Feedback is appreciated. Also: http://dev.rubyonrails.com/ticket/2588

Thanks!

- Fabien

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On Oct 31, 2005, at 2:30 AM, Fabien Franzen wrote:
> In my pursuit of a working acts_as_list for HasAndBelongsTo  
> associations I would like to propose the following:
>
> Currently HABTM uses raw sql to create and delete entries in the  
> join table. This way the normal AR flow is circumvented, including  
> all the normal callback functions (before_create, after_destroy ...)
>
> On the other hand, if you could specify that the join table should  
> be treated like a real model (AR object) when doing create and  
> delete on it, it would automatically enable a lot of options. Among  
> them, working acts_as_* functionality, since most of them are  
> dependent on callbacks.
Great thinking, Fabien.

In fact, this is the future of HABTM post-1.0.

Simplify,
jeremy
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> In fact, this is the future of HABTM post-1.0.
I hope this will make it soon!

I''ve tried to implement some of it today. But it didn''t work
out,
when I added:

has_and_belongs_to_many(options)
...

unless options[:join_model].nil?
     ...
     eval("before_destroy { |record| options[:join_model].destroy_all 
(<condition here>) }
else
     <regular before_destroy RAW SQL: DELETE FROM ...>
end

This is from the top of my head, since I deleted my changes out of  
frustration...

When doing anything destroy related now, it gives a MethodUndefined  
error. My guess is that it causes an infinite loop, which gets  
aborted before it will loop forever. If I change destroy_all to  
delete_all, this works fine, but off coarse, this doesn''t help a lot  
since this will circumvent the callbacks too.

Also, I''m new to Ruby (and Rails), but I do have a lot of experience  
in similar model structures and associations.

Anyway, I''m looking forward to contributing ideas, and eventually  
patches, when I master this some more.

Regards,

Fabien