FactoryBot::With

FactoryBot::With is a FactoryBot extension that enhances usability by wrapping factory methods.

For example, given these factories:

FactoryBot.define do
  factory(:blog)
  factory(:article) { blog }
  factory(:comment) { article }
end

Instead of writing like this:

create(:blog) do |blog|
  create(:article, blog:) { |article| create(:comment, article:) }
  create(:article, blog:) { |article| create_list(:comment, 3, article:) }
end

FactoryBot::With allows you to write like this:

create.blog do
  create.article { create.comment }
  create.article { create_list.comment(3) }
end

Installation

Add the following line to your Gemfile:

gem "factory_bot-with"

Then, instead of including FactoryBot::Syntax::Methods, include FactoryBot::With::Methods:

# RSpec example
RSpec.configure do |config|
  # ...
  config.include FactoryBot::With::Methods
  # ...
end

Alternatively, these factory methods are also provided as class methods of FactoryBot::With.

What differs from `FactoryBot::Syntax::Methods`?

Method-style syntax

FactoryBot::With overrides the behavior of factory methods called without arguments.

create(:foo, ...)  # normal usage
create             # returns a Proxy (an intermediate) object
create.foo(...)    # is equivalent to create(:foo, ...)

# This also applies to other factory methods:
build_stubbed.foo(...)
create_list.foo(10, ...)

Smarter interpretation of positional arguments

FactoryBot::With allows factory methods to accept Hash, Array, and falsy values (false or nil) as positional arguments¹.

create.foo({ title: "Recipe" }, is_new && %i[latest hot])
#=> create(:foo, :latest, :hot, title: "Recipe")  if is_new
#   create(:foo, title: "Recipe")                 otherwise

`with`, `with_pair`, and `with_list` operator

FactoryBot::With introduces new operators: with (and its family).

with(:factory_name, ...)
with_pair(:factory_name, ...)
with_list(:factory_name, number_of_items, ...)

These operators produce a With instance. This instance can be passed as an argument to factory methods such as build or create:

create.blog(with.article(with.comment))

When the factory method is called, it first collects and removes With arguments, then delegates the actual object creation to the standard FactoryBot factory method, and finally creates additional objects based on the factory definition. Above example is equivalent to:

_tmp1 = FactoryBot.create(:blog)
_tmp2 = FactoryBot.create(:article, blog: _tmp1)
_tmp3 = FactoryBot.create(:comment, article: _tmp2)
# Here, `blog: _tmp1` and `article: _tmp2` are automatically completed by AAR (described later)

Automatic Association Resolution (AAR)

with automatically resolves references to ancestor objects based on the definition in your FactoryBot factories.

This automatic resolution takes into account any traits, aliases, and factory specifications in the definition.

FactoryBot.define do
  factory(:video)
  factory(:photo)
  factory(:tag) do
    # `tag` potentially has an association on `taggable` field. `taggable` is either `video` or `photo`.
    trait(:for_video) { taggable factory: :video }
    trait(:for_photo) { taggable factory: :photo }
  end
end

create.video(with.tag(text: "latest"))  # resolved as `taggable: <created video object>`
create.photo(with.tag(text: "latest"))  # resolved as `taggable: <created photo object>`

Due to technical limitations, inline associations are not taken into account.

Factory Name Completion (FNC)

For a factory name that is prefixed by the ancestor object's factory name, the prefix can be omitted.

FactoryBot.define do
  factory(:blog)
  factory(:blog_article) { blog }
end

create.blog(with.article) # completes to :blog_article

Implicit context scope

FactoryBot::With factory methods can accept a block argument, just like standard FactoryBot. However, in FactoryBot::With, nested factory method calls within a block recognize ancestor objects. This means that nested factory method calls perform AAR and FNC in the same way as the with operator.

# Instead of writing:
create.blog(with.article(with.comment))
# You can write:
create.blog { create.article { create.comment } }
# ^ This works in the same way as:
create(:blog) do |blog|
  create(:article, blog:) do |article|
    create(:comment, article:)
  end
end

Incompatible behavior when calling _list or _pair factory methods with a block

To align the behavior with the with_list operator, there is an incompatible behavior compared to standard FactoryBot:

# This code creates a blog with 2 articles, each with a comment in standard FactoryBot:
# This does not work in FactoryBot::With!
create(:blog) do |blog|
  create_list(:article, 2, blog:) do |articles| # yielded *once* with an array of articles
    articles.each { |article| create(:comment, article:) }
  end
end

# In FactoryBot::With, blocks are yielded for each object. So we must write like this:
create.blog do |blog|
  create_list.article(2, blog:) do |article| # yielded *for each article*
    create.comment(article:)
  end
end

# Again, you can simplify this by (1)omitting the block or (2)using the `with` operator:
create.blog { create_list.article(2) { create.comment } }  # (1)
create.blog(with_list.article(2, with.comment))            # (2)

If you want to avoid this incompatibility, you can use Object#tap.

Additional features

Implicit context scope with existing objects

By calling with without positional arguments, but with keyword arguments that define the relationship between factory names and objects, along with a block, it creates a context scope where those objects become candidates for AAR and FNC.

let(:blog) { create.blog }

before do
  with(blog:) do
    # Just like `create.blog { ... }`,
    # the `blog` object is available for AAR and FNC in the following `create.article` calls:
    create.article(with.comment)
    create.article(with_list.comment(3))
  end
end

with_list works similarly to with, except that it accepts arrays as its values:

blog = create.blog
articles = create_list.article(2, blog:)
with_list(article: articles) { create.comment } # yielded *for each article*

`with` as a factory method call template

A With instance can also be used as a template for factory method calls.

Instead of writing:

let(:story) { create(:story, *story_args, **story_kwargs) }
let(:story_args) { [] }
let(:story_kwargs) { { category: "SF" } }

context "when published more than one year ago" do
  let(:story_args) { [*super(), :published] }
  let(:story_kwargs) { { **super(), start_at: 2.year.ago } }

  # ...
end

You can write like this:

# Factory methods accept a With instance as a first argument:
let(:story) { create(story_template) }
let(:story_template) { with.story(category: "SF") }

context "when published more than one year ago" do
  let(:story_template) { with(super(), :published, start_at: 2.year.ago) }

  # ...
end

Development

git clone https://github.com/yubrot/factory_bot-with
cd gems/factory_bot-with
bin/setup
bundle exec rake --tasks
bundle exec rake

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/yubrot/factory_bot-with. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the FactoryBot::With project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

The idea for this behavior came from JavaScript libraries such as clsx. ↩

factory_bot-with

Runtime