Rails first_or_create ActiveRecord method

Question

What does the first_or_create / first_or_create! method do in Rails?

According to the documentation, the method "has no description"...

Answer 1

From the Guides

first_or_create

The first_or_create method checks whether first returns nil or not. If it does return nil, then create is called. This is very powerful when coupled with the where method. Let’s see an example.

Suppose you want to find a client named ‘Andy’, and if there’s none, create one and additionally set his locked attribute to false. You can do so by running:

Client.where(:first_name => 'Andy').first_or_create(:locked => false)
# => #<Client id: 1, first_name: "Andy", orders_count: 0, locked: false, created_at: "2011-08-30 06:09:27", updated_at: "2011-08-30 06:09:27">

The SQL generated by this method looks like this:

SELECT * FROM clients WHERE (clients.first_name = 'Andy') LIMIT 1
BEGIN
INSERT INTO clients (created_at, first_name, locked, orders_count, updated_at) VALUES ('2011-08-30 05:22:57', 'Andy', 0, NULL, '2011-08-30 05:22:57')
COMMIT

first_or_create returns either the record that already exists or the new record. In our case, we didn’t already have a client named Andy so the record is created and returned.

first_or_create!

You can also use first_or_create! to raise an exception if the new record is invalid. Validations are not covered on this guide, but let’s assume for a moment that you temporarily add

validates :orders_count, :presence => true

to your Client model. If you try to create a new Client without passing an orders_count, the record will be invalid and an exception will be raised:

Client.where(:first_name => 'Andy').first_or_create!(:locked => false)
# => ActiveRecord::RecordInvalid: Validation failed: Orders count can't be blank