Getting Started

What is Fabrication?

Fabrication generates objects in Ruby. Fabricators are schematics for your objects, and can be created as needed anywhere in your app or specs.

Fabrication can generate anything, but has specific support for ActiveRecord Models, Mongoid Documents, Sequel Models, and DataMapper Resources.


Fabrication is tested against Ruby 2.5 and above.

To use it with Bundler, just add it to your gemfile.

gem 'fabrication'

Defining Fabricators

You can define a schematic for generating objects by defining Fabricators as spec/fabricators/**/*fabricator.rb.

Fabricators are loaded automatically - so as long as they’re in the right place, you’re good to go.

So let’s say you have a Person model with the usual fields and some associations:

class Person < ActiveRecord::Base
  belongs_to :neighborhood
  has_many :houses

You could then create a Fabricator to automaticaly generate copies of Person for your test suite.

# located in spec/fabricators/person_fabricator.rb

Fabricator(:person) do
  houses(count: 2)
  name { }
  age 45
  gender { %w(M F).sample }

Every time you fabricate a person, you’ll get a brand-new instance of a person model persisted to the database and containing the fields you specified. In the case above, neighborhood and houses would automatically expand out to use the fabricators for those models, and be persisted as well.

You can learn more on the Defining Fabricators tab.

Fabricating Instances

Once you’ve defined some fabricators, you can use them anywhere in your application. This is especially useful in populate scripts for development and staging environments, as well as in your test suite.

You can Fabricate a new instance of the person object we defined above every time you call:


You can also provide overrides to the default options at Fabricate time with a hash or the same block syntax you used to define the Fabricator.

Fabricate(:person, name: 'Paul Elliott', gender: 'M') do
  houses { [Fabricate(:house, location: 'the beach')] }

You can learn more about the options available at Fabricate time on the Fabricating Objects tab.

Getting Help

Email the fabrication mailing list if you need extra help or have specific questions. I’ll answer you as quick as I can.

If all else fails, open an issue on GitLab and I’ll take a look!


To override these settings, put a fabrication.rb in your support folder with a configure block

Fabrication.configure do |config|
  config.fabricator_path = 'data/fabricators'
  config.path_prefix = Rails.root
  config.sequence_start = 10000
  config.generators << CustomGeneratorForORM

Supported Options


Specifies the path within your project where Fabricator definitions are located.

Default: ['test/fabricators', 'spec/fabricators']


Allows you to specify the location of your application on the file system. This is especially useful when working with Rails engines.

Default: Rails.root if defined, otherwise '.'


Allows you to specify the default starting number for all sequences. This can still be overridden for specific sequences.

Default: 0


Allows you to specify custom generators for non officially supported ORMs.

Default: []

Pre-loading Fabricators

Fabrication doesn’t load the defined fabricators until the first time you actually try to fabricate something. Here is an example for pre-loading them in cucumber.

Before do

NOTE: The vast majority of users do not need to do this and I do not recommend it. Certain uses and instances require it though.

Defining Custom Generators

Fabrication has builtin support for most popular Ruby ORMs. If you want to implement your custom strategy for ActiveRecord or add support for a new ORM, you can add your own generator.

class ImmutablePoroGenerator < Fabrication::Generator::Base
  def self.supports?(klass)
    # return true or false, if this generator can support `klass` or not

  def build_instance
    self._instance =

Fabrication.configure do |config|
  config.generators << ImmutablePoroGenerator

Defining Fabricators


The first argument to the fabricator is the name you will use when fabricating objects or defining associations. It should be the symbolized form of the class name.

class Person; end

To use a different name from the class, you must specify from: :symbolized_class_name as the second argument.

Fabricator(:adult, from: :person)
Fabricator(:adult, from: "SomeNamespace::Person")

The value of :from can be either a class name string or symbol, or the name of another fabricator.


The Fabricator block does not require a block variable, but one can be supplied. You can list the attributes to be generated and they will be created in order of declaration.

Fabricator(:person) do
  name 'Greg Graffin'
  profession 'Professor/Musician'

To produce dynamic values, you can pass a block to the attribute.

Fabricator(:person) do
  name { }
  profession { %w(Butcher Baker Candlestick\ Maker).sample }

Attributes are processed in order of declaration and fields above the current one are available via a block parameter.

Fabricator(:person) do
  name { }
  email { |attrs| "#{attrs[:name].parameterize}" }

To assign a Hash value you must to do so inside a block. If you do not, Fabricate will treat is as the options argument to the fabricated attribute (where you would normally define a count, custom fabricator, etc).

Fabricator(:person) do
  settings do
    { favorite_color: 'yellow', egg_preference: 'scrambled' }


Using keywords for field names is not a best practice!

You can reference fields whose names are reserved keywords (alias, class, def, if, while, …) with the block variable.

class Person
  attr_accessor :alias, :codename
  alias aka codename

Fabricator(:person) do |f|
  f.alias 'James Bond'
  codename '007'

Fabricate(:person).aka #=> '007'


You can associate another fabricator by just writing the attribute name. Fabrication will look up a fabricator of that name, generate the object, and set it in the current object. This is great for belongs_to associations.

Fabricator(:person) do

… is equivalent to …

Fabricator(:person) do
  vehicle { Fabricate(:vehicle) }

You can specify which fabricator to use in that situation as well.

Fabricator(:person) do
  ride(fabricator: :vehicle)

… is equivalent to …

Fabricator(:person) do
  ride { Fabricate(:vehicle) }

You can also generate arrays of objects with the count parameter. The attribute block receives the object being generated as well as the incrementing value. It works just like you would expect if you leave off the block.

Fabricator(:person) do
  open_source_projects(count: 5)
  children(count: 3) { |attrs, i| Fabricate(:person, name: "Kid #{i}") }

Or for those times when you are trying to create random data with Fabrication…

Fabricator(:person) do
  open_source_projects(rand: 5)
  children(rand: 3) { |attrs, i| Fabricate(:person, name: "Kid #{i}") }
  dogs(rand: 1..4)
Handling Circular Relationships

If you have associations set up bi-directionally between two models you may see an issue of circular object generation. Fabricators producing that situation would look something like the following.

Fabricator(:widget) do
  wockets(count: 5)

Fabricator(:wocket) do

You have a couple of options for fixing this. One may be better than the other based on the usage situation.

1) Use a “base” version of the fabricator for the association. It’s basically a trimmed down version without the associations but it can still have all the local attributes.

Fabricator(:widget) do
  wockets(count: 5, fabricator: :wocket_base)

Fabricator(:wocket_base, class_name: :wocket)

Fabricator(:wocket, from: :wocket_base) do

2) Override the belongs_to generation. ActiveRecord will automatically set the belongs_to side of the relationship when you save the set when you leave it blank.

Fabricator(:widget) do
  wockets(count: 5) do
    Fabricate(:wocket, widget: nil)

Fabricator(:wocket) do


You can inherit attributes from other fabricators by using the :from attribute.

Fabricator(:llc, from: :company) do
  type "LLC"

Setting the :from option will inherit the class and all the attributes from the named Fabricator.

You can also explicitly specify the class being fabricated with the :class_name parameter.

Fabricator(:llc, class_name: :company) do
  type "LLC"

Custom Initialization

If your object requires custom initialization you can override the normal initialization means with the initialize_with option. This block receives a hash with any defined transients, which you can use to further customize the initialization of your object.

You can access the target class via the resolved_class getter method. It is available in the context of the initialize block and references the class constant determined by the Fabricator. In the below example resolved_class == Car.

Within the block you can reference any attribute defined in the fabricator as a local variable. In the below example we’re reading wheels inside the initialize_with block and using it to create the new object.

This block should return a new instance of an object. After this block executes attributes will be applied to the resulting object.

Fabricator(:car) do
  transient :color

  wheels { [3, 4, 6].sample }

  initialize_with do |transients|
    resolved_class.manufacture(wheels: wheels, color: transients[:color])

The object instantiated and returned by the initialize_with block will have all the defined attributes applied and it will be returned by the Fabricate method call.


Fabrication has its own callback cycle that is completely separate from the one provided by your ORM. You can use the following callbacks in your Fabricator definition.


IMPORTANT: The only callback executed when building an object is after_build. The rest are only executed when you create an object using the regular Fabricate call. However, when your Fabricator is automatically run via an association created for another Fabricator, it will only run the after_build callback.

You can define them in your Fabricators as a block that optionally receives the object being fabricated and a hash of any transient attributes defined. As with anything that works in the Fabricator, you can also define them when you call Fabricate and they will work just like you’d expect. The callbacks are also stackable, meaning that you can declare multiple of the same type in a fabricator and they will not be clobbered when you inherit another fabricator.

Fabricator(:place) do
  before_validation { |place, transients| place.geolocate! }
  after_create { |place, transients| Fabricate(:restaurant, place: place) }


You can provide aliases for a fabricator by supplying the :aliases option to the Fabricator call.

Fabricator(:thingy, aliases: [:widget, :wocket])

You can now call Fabricate with :thingy, :widget, or :wocket and receive back the generated object.

Transient Attributes

Transient attributes allow you to declare variables in the Fabricator that are not set in the generated class. You can interact with them during attribute generation as if they were regular attributes, but they are stripped out when the attributes are mass-assigned to the object.

Fabricator(:city) do
  transient :asian
  name { |attrs| attrs[:asian] ? "Tokyo" : "Stockholm" }
Fabricate(:city, asian: true)
  # => <City name: 'Tokyo'>

You can specify multiple transients by passing them all to transient.

Fabricator(:the_count) do
  transient :one, :two, :three

You can also specify default values with an options hash at the end.

Fabricator(:fruit) do
  transient :color, delicious: true

If you need to specify more complicated defaults you can treat it the same as a normal attribute.

Fabricator(:fruit) do
  transient :color

  color do
    'red' if variety == 'strawberry'


You can attach files to ActiveStorage by wrapping the local with Rack::Test::UploadedFile as in the example below. You don’t need to do anything special…ActiveStorage will just do the right thing.

Fabricator(:product) do
  my_file do'spec', 'fixtures', 'files', 'my-file.png'))


If you need to reset fabrication back to its original state after it has been loaded, call:


This is useful if you are using something like Spork and reloading the whole environment is not desirable.

Fabricating Objects

The Basics

The simplest way to Fabricate an object is to pass the Fabricator name into Fabricate.


That will return an instance of Person using the attributes you defined in the Fabricator.

To set additional attributes or override what is in the Fabricator, you can pass a hash to Fabricate with the fields you want to set.

Fabricate(:person, first_name: "Corbin", last_name: "Dallas")

The arguments to Fabricate always take precedence over anything defined in the Fabricator.

Fabricating With Blocks

In addition to the hash, you can pass a block to Fabricate and all the features of a Fabricator definition are available to you at object generation time.

Fabricate(:person, name: "Franky Four Fingers") do
  addiction "Gambling"
  fingers(count: 9)

The hash will overwrite any fields defined in the block.


If you don’t want to persist the object to the database, you can use and skip the save step. All the normal goodness when Fabricating is available for building as well.

When you invoke a build, all other Fabricate calls will be processed as build until the build completes. If the object being built causes other objects to be generated, they will not be persisted to the database either.

For example, calling build on person will cascade down to Fabricate(:car) and they will not be persisted either. do
  cars { { Fabricate(:car) } }

Attributes Hash

You can receive any object back in the form of a hash. This processes all the defined fields, but doesn’t actually create or persist the object. If ActiveSupport is available it will be a HashWithIndifferentAccess, otherwise it will be a regular Ruby Hash.


If the class you are getting the attributers for has a polymorphic belongs_to, you will need to add the type field to the fabricator definition if you want it in the generated parameters.

Fabricator(:comment) do
  commentable(fabricator: :post)
  commentable_type { |attrs| attrs[:commentable].class.to_s }

Multiple Objects

You can create an array of objects by using the times method. It takes an integer as the first argument and the rest has all the same goodness as the standard Fabricate method.

Fabricate.times(4, :company, name: 'Hashrocket') do
  type 'consultancy'

#=> an array with 4 company objects

The times method’s build equivalent to create an array of non-persistent objects is the build_times method.

Fabricate.build_times(4, :company, name: 'Hashrocket') do
  type 'consultancy'


A sequence allows you to get a series of numbers unique within the current process. Fabrication provides you with an easy and flexible means for keeping track of sequences.

You can create a sequence that starts at 0 anywhere in your app with a simple command.

  # => 0
  # => 1
  # => 2

You can name them by passing an argument to sequence.

  # => 0
  # => 1
  # => 2

If you want to specify the starting number, you can do it with a second parameter. It will always return the seed number on the first call and it will be ignored with subsequent calls.

Fabricate.sequence(:number, 99)
  # => 99
  # => 100
  # => 101

Alternatively, you can specify the starting point for all sequences globally with a configuration setting. (See Configuration tab)

If you are generating something like an email address, you can pass it a block and the block response will be returned.

Fabricate.sequence(:name) { |i| "Name #{i}" }
  # => "Name 0"
  # => "Name 1"
  # => "Name 2"

You can use the shorthand notation if you are using them in your fabricators.

Fabricate(:person) do
  ssn { sequence(:ssn, 111111111) }
  email { sequence(:email) { |i| "user#{i}" } }
# => <Person ssn: 111111111, email: "">
# => <Person ssn: 111111112, email: "">
# => <Person ssn: 111111113, email: "">


If you are using rspec-rails and fabrication gem is present in the :development Bundler group, fabricators will be generated automatically when you generate models.

To produce fabricators when you generate models with test-unit or minitest, you need to configure the test_framework and fixture_replacement options in your config/application.rb. Use this if you are using test-unit:

config.generators do |g|
  g.test_framework      :test_unit, fixture_replacement: :fabrication
  g.fixture_replacement :fabrication, dir: "test/fabricators"

… or this if you are using minitest:

config.generators do |g|
  g.test_framework      :minitest, fixture_replacement: :fabrication
  g.fixture_replacement :fabrication, dir: "test/fabricators"

Once it’s setup, a fabricator will be generated whenever you generate a model.

rails generate model widget

Will produce:

# test/fabricators/widget_fabricator.rb

Fabricator(:widget) do

Cucumber Steps


Packaged with the gem is a generator which will load some handy cucumber steps into your step_definitions folder.

rails generate fabrication:cucumber_steps

Step Definitions

With a Widget Fabricator defined, you can easily fabricate a single “widget”.

Given 1 widget

To fabricate a single “widget” with specified attributes:

Given the following widget:
    | name      | widget_1 |
    | color     | red      |
    | adjective | awesome  |

To fabricate multiple “widgets”:

Given 10 widgets

To fabricate multiple “widgets” with specified attributes:

Given the following widgets:
    | name     | color | adjective |
    | widget_1 | red   | awesome   |
    | widget_2 | blue  | fantastic |

To fabricate “wockets” that belong to widget you already fabricated:

And that widget has 10 wockets

To fabricate “wockets” with specified attributes that belong to your widget:

And that widget has the following wocket:
    | title    | Amazing |
    | category | fancy   |

That will use the most recently fabricated “widget” and pass it into the wocket Fabricator. That requires your “wocket” to have a setter for a “widget”.

In more complex cases where you’ve already created “widgets” and “wockets” and associated them with other objects, to set up an association between the former two:

And that wocket belongs to that widget

You can verify that some number of objects were persisted to the database:

Then I should see 1 widget in the database

You can also verify that a specific object was persisted:

Then I should see the following widget in the database:
    | name  | Sprocket |
    | gears | 4        |
    | color | green    |

That will look up the class defined in the fabricator for “widget” and run a where(…) with the parameterized table as an argument. It will verify that there is only one of these objects in the database, so be specific!


You can define transforms to apply to tables in the cucumber steps. They work on both vertical and horizontal tables and allow you to remap column values. You can provide string data and perform logic on it to set objects instead. You can put them in your spec/fabricators folder or whatever you have configured.

For example, you can define a transform on all fields named “company”. It will pass the strings from the cells into a lambda and set the return value to the attribute, in effect replacing the supplied company name with an actual instance of the company in the generated object.

Fabrication::Transform.define(:company, lambda{ |company_name| Company.where(name: company_name).first })

You can invoke it by putting the expected text in the cells and matching the column name to the symbol.

Scenario: a single object with transform to apply
  Given the following company:
    | name | Widgets Inc |
  Given the following division:
    | name    | Southwest   |
    | company | Widgets Inc |
  Then that division should reference that company
Scenario: multiple objects with transform to apply
  Given the following company:
    | name | Widgets Inc |
  Given the following divisions:
    | name      | company     |
    | Southwest | Widgets Inc |
    | North     | Widgets Inc |
  Then they should reference that company

When the divisions are generated, they will receive the company object as looked up by the lambda.

You can also scope them to a specific model with only_for.

Fabrication::Transform.only_for(:division, :company, lambda { |company_name| Company.where(name: company_name).first })


Getting Help

Email the fabrication mailing list if you need extra help or have specific questions.

You can also view the raw version of this documentation.

If all else fails, open an issue on GitLab.

Make Syntax

If you are migrating to Fabrication from Machinist, you can include make syntax to help ease the transition. Simply require fabrication/syntax/make and you will get make and make! mixed into your classes.

You can also provide a suffix to the class’s primary Fabricator.

Fabricator(:author_with_books, from: :author) do
  books(count: 2)



I (paulelliott) am actively maintaining this project. If you would like to contribute, please fork the project, make your changes with specs on a feature branch, and submit a pull request.

Naturally, the Fabrication source is available on GitLab as is the source for the Fabrication website.

To run rake successfully:

  1. Clone the project
  2. Install mongodb and sqlite3 (brew install …)
  3. Install bundler (gem install bundler)
  4. Run bundle from the project root
  5. Run rake and the test suite should be all green!