Rails 4 deprecation of in-place edit methods for collection associations

Hi everyone!

For those of you who are not noticed the in-place edit method for collection associations are broken in the current rails release - 4.0.0,

and here’s what is cooking in the rails master https://github.com/rails/rails/commit/1a40be02113287d9a003f8224e91b9f623857f4b

and this https://github.com/rails/rails/pull/12227

In short: it looks like things like has_many.reject!{}, has_many.select!{}, has_many.delete_if{}, has_many.pop etc. will not work as of Rails 4.2.

I tried to get some answers about the motivation of this decision here https://github.com/rails/rails/pull/12236 but i failed.

So to the question can someone please explain WHY is this happening?

Where is the “confusion” in the examples above?


I have read the CHANGELOG - it does not explain the motivation.

And please, I don’t thing that “This behavior was changed by design. We choose to not support this in Rails 4.0 and we will not bring it back” and “The decision was already made and like I said we will not change it back since it introduce more confusion than feature” are answers to my question at all.

Monkey patch gem to revert to per rails 4 behaviour rails4-editable-collections | RubyGems.org | your community gem host

Another related ticket: Rails 4.0 - delete_if() doesn't work as expected on has_many associations · Issue #12140 · rails/rails · GitHub

The problem is that using (for instance) delete_if on a collection removes things from the in-memory version but doesn’t persist the changes. It can’t persist the changes, since the records have been removed from the association’s list of records. This is EXACTLY the “confusion” referenced in the tickets.

One of your examples in 12236 highlights this issue: these two code snippets (in Rails 3 or 4) do not do the same thing:

post.comments.select! { |comment| comment.not_spam? }

=> filters the array in-memory but does not unlink objects


comments = post.comments.to_a

comments.select! { |comment| comment.not_spam? }

post.comments = comments

=> unlinks comments that aren’t in the filtered array

–Matt Jones

The justification for this change seems preposterous. Why would anyone think that, in the former example, the database has changed? The method called there is named “select!”.

This sounds like a case of a few people writing fragile code without any understanding of what they were doing or the systems they work on, and complaining about it. I suggested that a simple bit of documentation would solve the problem. It doesn’t seem to make much sense to make this particular interface so inconsistent with the rest of ActiveRecord, which absolutely allows you to modify objects in memory.

Thank you Matt!! Now I see my own confusion - I was convinced that these two snippets are identical in Rails 3 (Well, they are - JUST in MY case)

When they do the same thing - when the collection contains only new records (hence no unlinking required).

In all other cases in-place filtering doesn’t work even in Rails 3 as you pointed out.

But I still disagree that dropping the in-place methods (and breaking the Collection contract) is the best solution.

Thank you once again for clarifying!!