thoughtbot/factory_bot · error · FactoryBot::DuplicateDefinitionError

#{@component.name} already registered: #{name}

Error message

#{@component.name} already registered: #{name}

What it means

DuplicateDefinitionError raised by Decorator::DisallowsDuplicatesRegistry#register when FactoryBot.define registers a factory, trait, or sequence whose name is already in the registry. The factories, traits, and sequences registries are wrapped with this decorator; the message's first word comes from @component.name and tells you which registry collided (Factory/Trait/Sequence).

Source

Thrown at lib/factory_bot/decorator/disallows_duplicates_registry.rb:6

module FactoryBot
  class Decorator
    class DisallowsDuplicatesRegistry < Decorator
      def register(name, item)
        if registered?(name)
          raise DuplicateDefinitionError, "#{@component.name} already registered: #{name}"
        else
          @component.register(name, item)
        end
      end
    end
  end
end

View on GitHub (pinned to 18ae8b581b)

Solutions

1. Find the collision: `grep -rn 'factory :user' spec/` (or trait/sequence names) and delete or rename one definition.
2. If files are intentionally re-required (pry, reload tasks), call FactoryBot.reload between loads to clear registries first.
3. Compose variations with traits instead of duplicating whole factories (`factory :user` + `trait :admin`).
4. Guard conditional definitions: `unless FactoryBot.factories.registered?(:user)`.

Example fix

# before
# spec/factories/user.rb
FactoryBot.define { factory :user { name { 'Plain' } } }
# spec/factories/admin.rb (same run)
FactoryBot.define { factory :user { name { 'Admin' } } } # DuplicateDefinitionError

# after
# one file, variations via traits
FactoryBot.define do
  factory :user do
    name { 'Plain' }

    trait :admin do
      name { 'Admin' }
    end
  end
end

# guard against re-registration, e.g. in reloaded spec helpers
name = :user
if FactoryBot.factories.registered?(name)
  warn "skipping re-definition of :user"
else
  FactoryBot.define { factory(name) { name { 'Plain' } } }
end

->(name) { !FactoryBot.factories.registered?(name) }

begin
  FactoryBot.define { #...
 }
rescue FactoryBot::DuplicateDefinitionError => e
  # e.message names the registry and the duplicate; rename/remove one, or FactoryBot.reload
end

When it happens

Trigger: Two `factory :user` blocks loaded in the same run (same file, or two files under spec/factories); defining a global sequence with the same name twice; re-requiring a factories file from multiple spec helpers without FactoryBot.reload in between; `FactoryBot.define` executed again in a rake task or console session after definitions are already loaded.

Common situations: Copy-pasted factory files; spec support files required multiple times; reloading code in a rails console or with Spring where definitions persist; monorepos or shared engines where two apps define `factory :user`; renaming a factory while leaving the old definition behind.

Related errors

• Association '#{name}' received an invalid factory argument.
• Association '#{name}' received an invalid attribute override
• undefined method '#{name}' in '#{@definition.name}' factory
• Unexpected block passed to '#{name}' association in '#{@defi
• Attribute already defined: #{attribute.name}

AI-assisted analysis of thoughtbot/factory_bot@18ae8b581b (2026-08-21). Data as JSON: /api/errors/595b723a98784084. Report an issue: GitHub.