Compact db design a bad idea?


I have tried two db designs and both can work but I wonder which one
the Rails Gurus would go with. This is a general db design question
that has cropped up in a few situation. Here is the example I’ve been
working on.

In an online store, categories has_and_belongs_to_many images and
products has_and_belongs_to_many images. The db has the basic three


  • id
  • name


  • id
  • name


  • id
  • filename

What I can’t decide on is how to do the join tables.

Option 1 - would have many join tables and require many join models.
(The join models are to use the position field for acts_as_list to
order the images)


  • category_id
  • image_id


  • product_id
    _ image_id

Option 2 - have a one generic join table and only one join model


  • owner_class
  • owner_id
  • image_id

In option 2 a record could be (Category, 2, 3) or (Product, 4, 1)

Option 1 seems simpler but could lead to some repetitive code (at
least in the data base definition).

Option 2 is a little more complicated and I don’t know how it fits
into the normalization stuff.

How do I choose?


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