method

find_or_create_by

v4.1.8 - Show latest stable - 2 notes - Class: ActiveRecord::Relation

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What's this?

find_or_create_by(attributes, &block) public

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 "PenÃ©lope" or create a new one.
User.find_or_create_by(first_name: 'PenÃ©lope')
# => #<User id: 1, first_name: "PenÃ©lope", last_name: nil>

# Find the first user named "PenÃ©lope" or create a new one.
# We already have one so the existing record will be returned.
User.find_or_create_by(first_name: 'PenÃ©lope')
# => #<User id: 1, first_name: "PenÃ©lope", 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

Show source

# File activerecord/lib/active_record/relation.rb, line 207
    def find_or_create_by(attributes, &block)
      find_by(attributes) || create(attributes, &block)
    end

June 19, 2015

1 thank

Use :where or any defined scope before :find_or_create_by

You can chain find_or_create_by with :where, or any custom scope.

E.g.:

User.where(girls: true).find_or_create_by(first_name: ‘Scarlett’)

scope :celebrities, -> { where(celebrity: true) }

User.celebrities.create_with(last_name: ‘Johansson’).find_or_create_by(first_name: ‘Scarlett’)

find_or_create_by

Related methods

Use :where or any defined scope before :find_or_create_by

Are those supported versions correct?