# ExMachina
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[](https://hex.pm/packages/ex_machina)
[](https://hexdocs.pm/ex_machina/)
[](https://hex.pm/packages/ex_machina)
[](https://github.com/beam-community/ex_machina/blob/master/LICENSE)
[](https://github.com/beam-community/ex_machina/commits/master)
ExMachina makes it easy to create test data and associations. It works great
with Ecto, but is configurable to work with any persistence library.
> **This README follows the main branch, which may not be the currently published version**. Here are the
[docs for the latest published version of ExMachina](https://hexdocs.pm/ex_machina/readme.html).
## Installation
In `mix.exs`, add the ExMachina dependency:
<!-- {x-release-please-start-version} -->
```elixir
def deps do
[
{:ex_machina, "~> 2.8.0", only: :test},
]
end
```
<!-- {x-release-please-end} -->
Add your factory module inside `test/support` so that it is only compiled in the
test environment.
Next, be sure to start the application in your `test/test_helper.exs` before
ExUnit.start:
```elixir
{:ok, _} = Application.ensure_all_started(:ex_machina)
```
#### Install in just the test environment for non-Phoenix projects
You will follow the same instructions as above, but you will also need to add
`test/support` to your compilation paths (elixirc_paths) if you have not done
so already.
In `mix.exs`, add test/support to your elixirc_paths for just the test env.
```elixir
def project do
[app: ...,
# Add this if it's not already in your project definition.
elixirc_paths: elixirc_paths(Mix.env)]
end
# This makes sure your factory and any other modules in test/support are compiled
# when in the test environment.
defp elixirc_paths(:test), do: ["lib", "test/support"]
defp elixirc_paths(_), do: ["lib"]
```
## Overview
[Check out the docs](https://hexdocs.pm/ex_machina/ExMachina.html) for more details.
Define factories:
```elixir
defmodule MyApp.Factory do
# with Ecto
use ExMachina.Ecto, repo: MyApp.Repo
# without Ecto
use ExMachina
def user_factory do
%MyApp.User{
name: "Jane Smith",
email: sequence(:email, &"email-#{&1}@example.com"),
role: sequence(:role, ["admin", "user", "other"]),
}
end
def article_factory do
title = sequence(:title, &"Use ExMachina! (Part #{&1})")
# derived attribute
slug = MyApp.Article.title_to_slug(title)
%MyApp.Article{
title: title,
slug: slug,
# another way to build derived attributes
tags: fn article ->
if String.contains?(article.title, "Silly") do
["silly"]
else
[]
end
end,
# associations are inserted when you call `insert`
author: build(:user)
}
end
# derived factory
def featured_article_factory do
struct!(
article_factory(),
%{
featured: true,
}
)
end
def comment_factory do
%MyApp.Comment{
text: "It's great!",
article: build(:article),
}
end
end
```
Using factories ([check out the docs](https://hexdocs.pm/ex_machina/ExMachina.html) for more details):
```elixir
# `attrs` are automatically merged in for all build/insert functions.
# `build*` returns an unsaved comment.
# Associated records defined on the factory are built.
attrs = %{body: "A comment!"} # attrs is optional. Also accepts a keyword list.
build(:comment, attrs)
build_pair(:comment, attrs)
build_list(3, :comment, attrs)
# `insert*` returns an inserted comment. Only works with ExMachina.Ecto
# Associated records defined on the factory are inserted as well.
insert(:comment, attrs)
insert_pair(:comment, attrs)
insert_list(3, :comment, attrs)
# `params_for` returns a plain map without any Ecto specific attributes.
# This is only available when using `ExMachina.Ecto`.
params_for(:comment, attrs)
# `params_with_assocs` is the same as `params_for` but inserts all belongs_to
# associations and sets the foreign keys.
# This is only available when using `ExMachina.Ecto`.
params_with_assocs(:comment, attrs)
# Use `string_params_for` to generate maps with string keys. This can be useful
# for Phoenix controller tests.
string_params_for(:comment, attrs)
string_params_with_assocs(:comment, attrs)
```
## Delayed evaluation of attributes
`build/2` is a function call. As such, it gets evaluated immediately. So this
code:
```elixir
insert_pair(:account, user: build(:user))
```
Is equivalent to this:
```elixir
user = build(:user)
insert_pair(:account, user: user) # same user for both accounts
```
Sometimes that presents a problem. Consider the following factory:
```elixir
def user_factory do
%{name: "Gandalf", email: sequence(:email, "gandalf#{&1}@istari.com")}
end
```
If you want to build a separate `user` per `account`, then calling
`insert_pair(:account, user: build(:user))` will not give you the desired
result.
In those cases, you can delay the execution of the factory by passing it as an
anonymous function:
```elixir
insert_pair(:account, user: fn -> build(:user) end)
```
You can also do that in a factory definition:
```elixir
def account_factory do
%{user: fn -> build(:user) end}
end
```
You can even accept the parent record as an argument to the function:
```elixir
def account_factory do
%{user: fn account -> build(:user, vip: account.premium) end}
end
```
Note that the `account` passed to the anonymous function is only the struct
after it's built. It's not an inserted record. Thus, it does not have data that
is only accessible after being inserted into the database (e.g. `id`).
## Full control of factory
By default, ExMachina will merge the attributes you pass into build/insert into
your factory. But if you want full control of your attributes, you can define
your factory as accepting one argument, the attributes being passed into your
factory.
```elixir
def custom_article_factory(attrs) do
title = Map.get(attrs, :title, "default title")
article = %Article{
author: "John Doe",
title: title
}
# merge attributes and evaluate lazy attributes at the end to emulate
# ExMachina's default behavior
article
|> merge_attributes(attrs)
|> evaluate_lazy_attributes()
end
```
**NOTE** that in this case ExMachina will _not_ merge the attributes into your
factory, and it will not evaluate lazy attributes. You will have to do this on
your own if desired.
### Non-map factories
Because you have full control of the factory when defining it with one argument,
you can build factories that are neither maps nor structs.
```elixir
# factory definition
def room_number_factory(attrs) do
%{floor: floor_number} = attrs
sequence(:room_number, &"#{floor_number}0#{&1}")
end
# example usage
build(:room_number, floor: 5)
# => "500"
build(:room_number, floor: 5)
# => "501"
```
**NOTE** that you cannot use non-map factories with Ecto. So you cannot
`insert(:room_number)`.
## Usage in a test
```elixir
# Example of use in Phoenix with a factory that uses ExMachina.Ecto
defmodule MyApp.MyModuleTest do
use MyApp.ConnCase
# If using Phoenix, import this inside the using block in MyApp.ConnCase
import MyApp.Factory
test "shows comments for an article" do
conn = conn()
article = insert(:article)
comment = insert(:comment, article: article)
conn = get conn, article_path(conn, :show, article.id)
assert html_response(conn, 200) =~ article.title
assert html_response(conn, 200) =~ comment.body
end
end
```
## Where to put your factories
If you are using ExMachina in all environments:
> Start by creating one factory module (such as `MyApp.Factory`) in
`lib/my_app/factory.ex` and putting all factory definitions in that module.
If you are using ExMachina in only the test environment:
> Start by creating one factory module (such as `MyApp.Factory`) in
`test/support/factory.ex` and putting all factory definitions in that module.
Later on you can easily create different factories by creating a new module in
the same directory. This can be helpful if you need to create factories that are
used for different repos, your factory module is getting too big, or if you have
different ways of saving the record for different types of factories.
### Splitting factories into separate files
This example shows how to set up factories for the testing environment. For setting them in all environments, please see the _To install in all environments_ section
> Start by creating main factory module in `test/support/factory.ex` and name it `MyApp.Factory`. The purpose of the main factory is to allow you to include only a single module in all tests.
```elixir
# test/support/factory.ex
defmodule MyApp.Factory do
use ExMachina.Ecto, repo: MyApp.Repo
use MyApp.ArticleFactory
end
```
The main factory includes `MyApp.ArticleFactory`, so let's create it next. It might be useful to create a separate directory for factories, like `test/factories`. Here is how to create a factory:
```elixir
# test/factories/article_factory.ex
defmodule MyApp.ArticleFactory do
defmacro __using__(_opts) do
quote do
def article_factory do
%MyApp.Article{
title: "My awesome article!",
body: "Still working on it!"
}
end
end
end
end
```
This way you can split your giant factory file into many small files. But what about name conflicts? Use pattern matching to avoid them!
```elixir
# test/factories/post_factory.ex
defmodule MyApp.PostFactory do
defmacro __using__(_opts) do
quote do
def post_factory do
%MyApp.Post{
body: "Example body"
}
end
def with_comments(%MyApp.Post{} = post) do
insert_pair(:comment, post: post)
post
end
end
end
end
# test/factories/video_factory.ex
defmodule MyApp.VideoFactory do
defmacro __using__(_opts) do
quote do
def video_factory do
%MyApp.Video{
url: "example_url"
}
end
def with_comments(%MyApp.Video{} = video) do
insert_pair(:comment, video: video)
video
end
end
end
end
```
If you place your factories outside of `test/support` make sure they will compile by adding that directory to the compilation paths in your `mix.exs` file. For example for the `test/factories` files above you would modify your file like so:
```elixir
# ./mix.exs
...
defp elixirc_paths(:test), do: ["lib", "test/factories", "test/support"]
...
```
## Ecto
### Ecto Associations
ExMachina will automatically save any associations when you call any of the
`insert` functions. This includes `belongs_to` and anything that is
inserted by Ecto when using `Repo.insert!`, such as `has_many`, `has_one`,
and embeds. Since we automatically save these records for you, we advise that
factory definitions only use `build/2` when declaring associations, like so:
```elixir
def article_factory do
%Article{
title: "Use ExMachina!",
# associations are inserted when you call `insert`
comments: [build(:comment)],
author: build(:user),
}
end
```
Using `insert/2` in factory definitions may lead to performance issues and bugs,
as records will be saved unnecessarily.
### Passing options to Repo.insert!/2
`ExMachina.Ecto` uses
[`Repo.insert!/2`](https://hexdocs.pm/ecto/Ecto.Repo.html#c:insert!/2) to
insert records into the database. Sometimes you may want to pass options to deal
with multi-tenancy or return some values generated by the database. In those
cases, you can use `c:ExMachina.Ecto.insert/3`:
For example,
```elixir
# return values from the database
insert(:user, [name: "Jane"], returning: true)
# use a different prefix
insert(:user, [name: "Jane"], prefix: "other_tenant")
```
## Flexible Factories with Pipes
```elixir
def make_admin(user) do
%{user | admin: true}
end
def with_article(user) do
insert(:article, user: user)
user
end
build(:user) |> make_admin |> insert |> with_article
```
## Using with Phoenix
If you want to keep the factories somewhere other than `test/support`,
change this line in `mix.exs`:
```elixir
# Add the folder to the end of the list. In this case we're adding `test/factories`.
defp elixirc_paths(:test), do: ["lib", "test/support", "test/factories"]
```
## Custom Strategies
You can use ExMachina without Ecto, by using just the `build` functions, or you
can define one or more custom strategies to use in your factory. You can also
use custom strategies with Ecto. Here's an example of a strategy for json
encoding your factories. See the docs on [ExMachina.Strategy] for more info.
[ExMachina.Strategy]: https://hexdocs.pm/ex_machina/ExMachina.Strategy.html
```elixir
defmodule MyApp.JsonEncodeStrategy do
use ExMachina.Strategy, function_name: :json_encode
def handle_json_encode(record, _opts) do
Poison.encode!(record)
end
end
defmodule MyApp.Factory do
use ExMachina
# Using this will add json_encode/2, json_encode_pair/2 and json_encode_list/3
use MyApp.JsonEncodeStrategy
def user_factory do
%User{name: "John"}
end
end
# Will build and then return a JSON encoded version of the user.
MyApp.Factory.json_encode(:user)
```
## Contributing
Before opening a pull request, please open an issue first.
git clone https://github.com/thoughtbot/ex_machina.git
cd ex_machina
mix deps.get
mix test
Once you've made your additions and `mix test` passes, go ahead and open a PR!
## License
ExMachina is Copyright © 2015 thoughtbot. It is free software, and may be
redistributed under the terms specified in the [LICENSE](/LICENSE) file.
## About thoughtbot
ExMachina is maintained and funded by thoughtbot, inc.
The names and logos for thoughtbot are trademarks of thoughtbot, inc.
We love open source software, Elixir, and Phoenix. See [our other Elixir
projects][elixir-phoenix], or [hire our Elixir Phoenix development team][hire]
to design, develop, and grow your product.
[elixir-phoenix]: https://thoughtbot.com/services/elixir-phoenix?utm_source=github
[hire]: https://thoughtbot.com?utm_source=github
## Inspiration
* [Fixtures for Ecto](https://blog.danielberkompas.com/elixir/2015/07/16/fixtures-for-ecto.html)
* [Factory Bot](https://github.com/thoughtbot/factory_bot)
