Kohana (KO3) ORM universal pivot table (fields: model1, model1_id, model2, model2_id) — possible?

Question

I have the following setup of models:

User
   - has_many File (for userpics)

Gallery
   - has_many File (for images)

Page
   - has_one File (for background image)

Page object could share a File object with one or more Gallery objects for its background. And at some stage later a new model like

Product
   - has_many File

or similar can appear in the App.

Note that i need a File model instead of just storing paths to the actual files because the File model can reference, in fact, several files in the filesystem

File
   - id
   - path
   - path_poster
   - path_m4v     (HTML5 videos need up to three files for compatibility)
   - path_webm
   - path_ogv
   - width
   - height
   - poster_width
   - poster_height
   - type
   - ... etc....

So, is there a simple way (without overwriting the whole ORM class) to implement relationships that would use a "generic" pivot table with the following fields:

model_name VARCHAR(8) (or model_type_id TINYINT for speed)
model_id INT
file_id INT
relation_name VARCHAR(8)  (e.g., Page model can have "background" and "logo" relation)
position INT

The reason: i want to have a universal App module for checking for "orphaned" files, and also be able to tell to what each file is attached, so, for example, when deleting a file from the Gallery the App would warn that the file is still attached to a Page as background.

Answer 1

Short answer is no. The reason is because model_id would conflict with other model IDs. If you wanted, you could do a unique index on model_name+model_id, but to join those two columns would require that you rewrite the ORM methods to join models together via their relationships.

I would honestly stick with simple pivot tables.