Is there a way to avoid automatically updating Rails timestamp fields?

Question

If you have DB columns created_at and updated_at Rails will automatically set those values when you create and update a model object. Is there a way to save the model without touching those columns?

I am bringing in some legacy data and I would like to set those values from the corresponding values in the (differently named) legacy data fields. I'm finding when I set them on the model and then save the model, Rails appears to override the incoming values.

Of course I could just name the Rails model columns differently to prevent that, but after the data is imported, I want Rails to do its automatic timestamp thing.

Answer 1

You can set the following inside your migration:

ActiveRecord::Base.record_timestamps = false

Or altenatively use update_all:

update_all(updates, conditions = nil, options = {})

Updates all records with details given if they match a set of conditions supplied, limits and order can also be supplied. This method constructs a single SQL UPDATE statement and sends it straight to the database. It does not instantiate the involved models and it does not trigger Active Record callbacks.

Answer 2

Since this is a one-time import, you could do the following:

1. Create model using legacy_created_at and legacy_updated_at fields.
2. Load legacy data. Map into the model fields as desired. You can use #save and generally not worry about using update_all or the like, and you can use callbacks if desired.
3. Create a migration to rename the columns to created_at and updated_at.

Answer 3

Do this in a migration or in a rake task (or in the new database seeds if you're on edge rails):

ActiveRecord::Base.record_timestamps = false
run_the_code_that_imports_the_data

You can safely set created_at and updated_at manually, Rails won't complain.