A factory_bot set up supports two levels of sequences: global and factory-specific.

Global sequences

With a Factory.define block, use the sequence method to define global sequences that can be shared with other factories.

The sequence method takes a name, optional arguments, and a block. The name is expected to be a Symbol.

The supported arguments are a number representing the starting value (default: 1), and :aliases (default []). The starting value must respond to #next.

The block takes a value as an argument, and returns a result.

The sequence value is incremented globally. Using an :email_address sequence from multiple places increments the value each time.

See method_missing for a shorthand.

Factory sequences

Sequences can be localized within factory blocks. The syntax is the same as for a global sequence, but the scope of the incremented value is limited to the factory definition.

In addition, using sequence with a factory block implicitly calls add_attribute for that value.

These two are similar, except the second example does not cause any global sequences to exist:

# A global sequence
sequence(:user_factory_email) { |n| "person#{n}" }

factory :user do
  # Using a global sequence
  email { generate(:user_factory_email) }
# A factory-scoped sequence
factory :user do
  sequence(:email) { |n| "person#{n}" }