Question: Is it possible to reference the "current" attribute value when overriding it?

[Epigene]

Hi,

I've been using this gem for a couple years, so I think I know my way around, but this one has got me stumped. I know I can reference other attributes when setting some attribute, but what about referencing the "current" value of the field itself?

With JSON fields becoming more prominent, I have found the need to merge some default hash with additional options more prominent. Consider:

FactoryBot.define do
  factory :payload do
    transient do
      options { {} }
    end

    data { {default: "true"}.merge(options) }

    trait :custom do
       options { {default: "false"} }
    end
  end
end

Now I can do either:

create(:payload, :custom) or create(:payload, options: {default: "false"}), to get a "{default => "false"}" payload.

However, I can not do create(:payload, :custom, options: {additional: "yup"}) to get a {default: "false", additional: "yup"}} payload.

It would all be solved if I could access options to merge with the value e.g.:

FactoryBot.define do
  factory :payload do
    transient do
      options { {} }
    end

    data { {default: "true"}.merge(options) }

    trait :custom do
       options { options.merge(default: "false") } # options can not reference itself :(
    end
  end
end

Obviously, the example above causes an infinite loop and a stack error.

Is what I want possible? Maybe I am approaching this all wrong..

[mikegee]

Maybe merge the options into the data from an after(:build) callback?

[Epigene]

While after(:build) does provide a more flexible assignment alternative, the issue is not merging data with options, but options with more options.

[composerinteralia]

You could use two different transient attributes for this:

FactoryBot.define do
  factory :payload do
    transient do
      default_options { { default: "true" } }
      options { {} }
    end

    data { default_options.merge(options) }

    trait :custom do
      default_options { {default: "false"} }
    end
  end
end

It makes sense that options { options.merge(default: "false") } wouldn't work. Internally this defines an options method on an evaluator object. When we call that method, it executes the block in the context of the evaluator object (using instance_eval). So options { options } ends up being a recursive call to the same method.