Which callback does ActiveRecord use to record timestamp?

Question

I'm just wondering here whether any of you guys know when ActiveRecord use it's "magic" to record the timestamp (e.g. created_at, updated_at).

What i mean when is, at which callback ? (if AR use callback at all).

I'm asking this because I want to create an auto-updating column (that record sequential number for each object) and I want to replicate AR way to do this as much as possible.

EDITED: It seems that AR does it between after_validation and before_create/before_update. You can do some tests for this by creating a presence validation for created_at column and inserting new record with blank created_at, it would return an error.

Answer 1

I don't know where AR does it, but the proper place for what you describe sounds like before_create

Answer 2

In Rails 3.2.12, this code is located in lib/active_record/timestamp.rb.

As you mention in your question and DGM suggests, Rails will update the timestamps when creating or updating, so sticking your code in before_create and before_update should work.

You may also want to take a look at the ActiveRecord counter_cache functionality. ActiveRecord supports creation of a column that can automatically be incremented/decremented. Additionally, you can perform more complicated logic.