Custom Strategies

There are times where you may want to extend behavior of factory_bot by adding a custom build strategy.

Strategies define two methods: association and result. association receives a FactoryBot::FactoryRunner instance, upon which you can call run, overriding the strategy if you want. The second method, result, receives a FactoryBot::Evaluation instance. It provides a way to trigger callbacks (with notify), object or hash (to get the result instance or a hash based on the attributes defined in the factory), and create, which executes the to_create callback defined on the factory.

To understand how factory_bot uses strategies internally, it's probably easiest to view the source for each of the four default strategies.

Here's an example of composing a strategy using FactoryBot::Strategy::Create to build a JSON representation of your model.

class JsonStrategy
  def initialize
    @strategy = FactoryBot.strategy_by_name(:create).new

  delegate :association, to: :@strategy

  def result(evaluation)

  def to_sym

For factory_bot to recognize the new strategy, you can register it:

FactoryBot.register_strategy(:json, JsonStrategy)

This allows you to call


Finally, you can override factory_bot's own strategies if you'd like by registering a new object in place of the strategies.