Finds the first record with the given attributes, or creates a record with the attributes if one is not found:
# Find the first user named "Penélope" or create a new one. User.find_or_create_by(first_name: 'Penélope') # => #<User id: 1, first_name: "Penélope", last_name: nil> # Find the first user named "Penélope" or create a new one. # We already have one so the existing record will be returned. User.find_or_create_by(first_name: 'Penélope') # => #<User id: 1, first_name: "Penélope", last_name: nil> # Find the first user named "Scarlett" or create a new one with # a particular last name. User.create_with(last_name: 'Johansson').find_or_create_by(first_name: 'Scarlett') # => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">
This method accepts a block, which is passed down to create.
The last example above can be alternatively written this way:
# Find the first user named "Scarlett" or create a new one with a # different last name. User.find_or_create_by(first_name: 'Scarlett') do |user| user.last_name = 'Johansson' end # => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">
This method always returns a record, but if creation was attempted and
failed due to validation errors it won't be persisted, you get what
create returns in such situation.
Please note *this method is not atomic*, it runs first a SELECT, and if there are no results an INSERT is attempted. If there are other threads or processes there is a race condition between both calls and it could be the case that you end up with two similar records.
Whether that is a problem or not depends on the logic of the application, but in the particular case in which rows have a UNIQUE constraint an exception may be raised, just retry:
begin CreditAccount.find_or_create_by(user_id: user.id) rescue ActiveRecord::RecordNotUnique retry end
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