CODEWITHSUNDEEP
ruby-on-railsrubyruby-on-rails-4
Andrew K
Andrew K

Reputation: 1599

Rails Magic Method model_ids?

I was trying to look up how to get just the IDs of Comments, an associated model to Post.

Post has_many Comments

I found through the Rails documentation that you can use the .map method to pluck out just the IDs.

But then, for the heck of it, I tried doing:

p = Post.find(1)
p.comment_ids #[1,2,3]

And it worked! I cannot find this magic-method documented anywhere in the Rails docs. Is this an officially supported way to get has_many relation ids?

Upvotes: 2

Views: 619

Answers (2)

Arup Rakshit
Arup Rakshit

Reputation: 118271

If you look at the doco of has-many-association, you will find the detailed documentation.

collection_singular_ids:

... these methods, collection is replaced with the symbol passed as the first argument to has_many, and collection_singular is replaced with the singularized version of that symbol.

As per the singularize method -

comments.singularize # => comment

In your case collection_singular has been replaced with comment. That's how you got comment_ids method.

Hope it clears to you.

Upvotes: 1

awendt
awendt

Reputation: 13663

See the has_many Association Reference:

When you declare a has_many association, the declaring class automatically gains 16 methods related to the association:

Among them are:

collection_singular_ids
collection_singular_ids=ids

Upvotes: 2

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