ex_machina v2.2.0 ExMachina.Strategy View Source

Module for making new strategies for working with factories


defmodule MyApp.JsonEncodeStrategy do
  # The function_name will be used to generate functions in your factory
  # This example adds json_encode/1, json_encode/2, json_encode_pair/2 and json_encode_list/3
  use ExMachina.Strategy, function_name: :json_encode

  # Define a function for handling the records.
  # Takes the form of "handle_#{function_name}"
  def handle_json_encode(record, _opts) do

defmodule MyApp.JsonFactory do
  use ExMachina
  use MyApp.JsonEncodeStrategy

  def user_factory do
    %User{name: "John"}

# Will build and then return a JSON encoded version of the user.

The arguments sent to the handling function are

1) The built record 2) The options passed to the strategy

The options sent as the second argument are always converted to a map. The options are anything you passed when you use your strategy in your factory, merged together with %{factory_module: FactoryItWasCalledFrom}.

This allows for customizing the strategy, and for calling other functions on the factory if needed.

See ExMachina.EctoStrategy in the ExMachina repo, and the docs for name_from_struct/1 for more examples.

Link to this section Summary


Returns the factory name from a struct. Useful for strategies with callbacks

Link to this section Functions

Link to this function name_from_struct(struct) View Source
name_from_struct(struct) :: atom

Returns the factory name from a struct. Useful for strategies with callbacks.

This function can be useful when you want to call other functions based on the type of struct passed in. For example, if you wanted to call a function on the factory module before JSON encoding.


ExMachina.Strategy.name_from_struct(%User{}) # Returns :user
ExMachina.Strategy.name_from_struct(%MyUser{}) # Returns :my_user
ExMachina.Strategy.name_from_struct(%MyApp.MyTask{}) # Returns :my_task

Implementing callback functions with name_from_struct/1

defmodule MyApp.JsonEncodeStrategy do
  use ExMachina.Strategy, function_name: :json_encode

  def handle_json_encode(record, %{factory_module: factory_module}) do
    # If the record was a %User{} this would return :before_encode_user
    callback_func_name = :"before_encode_#{ExMachina.Strategy.name_from_struct(record)}"

    if callback_defined?(factory_module, callback_func_name) do
      # First call the callback function
      apply(factory_module, callback_func_name, [record])
      # Then encode it
      |> Poison.encode!
      # Otherwise, encode it without calling any callback

  defp callback_defined?(module, func_name) do
    Code.ensure_loaded?(module) && function_exported?(module, func_name, 1)