How do variable Model names work in CakePHP tables?

Question

Looking at the tables (aros, acos) generated by the ACL component and for example the Favorites plugin by CakeDC I see the favorites table with the fields Favorite.user_id, Favorite.model and Favorite.foreign_key.
The last two combined are replacing the good old Favorite.post_id (presuming model has the value 'Post'). It is in a way a HABTM pivot table with a dynamic modelname on one side.
I can see the general and useful idea here but would like to know more about the application of it.

My question(s):

• Does this pattern have a name?
• How does this work code-wise? I can see the abstract principle, but what kind of model-code is needed to make this work? Does it involve a patchwork of queries, or does this allow for a smooth one-query implementention? E.g.: I'd like to fetch all marked-as-favorite Posts in the system and their related Users in one go.
• And does this work both ways? (querying from both the Post model as well as the User model)

I'd like to work towards an abstraction where I put a behavior in place to take care of this pattern. I did look into the CakeDC code but could not figure out the principle. It's a little too cryptic for my current knowledge. Hence my question here.

kind regards,
Bart

Answer 1

Does this pattern have a name?

http://en.wikipedia.org/wiki/Junction_table aka Join Table.

How does this work code-wise? I can see the abstract principle, but what kind of model-code is needed to make this work? Does it involve a patchwork of queries, or does this allow for a smooth one-query implementention? E.g.: I'd like to fetch all marked-as-favorite Posts in the system and their related Users in one go.

It is just a regular join table, that's all. You can simply rely on what CakePHP is building up when using the HABTM assocs or refine your query by using joins. See http://book.cakephp.org/2.0/en/models/associations-linking-models-together.html#joining-tables.

The model field is not needed in that "pattern" but allows you to have just one join table that can be used for many different tables/models. For example instead of having tags and users and posts associated by tags_posts and tags_users we simply use the same table and filter by the model field.

And does this work both ways? (querying from both the Post model as well as the User model)

Yes if you set the HABTM association up in both models.

Thanks for using our plugins. ;)