When do boolean fields transform to true/false in Rails?

Question

In conversations with a teammate, we were asking ourselves when Rails turns values given to a boolean field into true/false.

In Rails, saving a value from certain certain "FALSE_VALUES" (like false, 'FALSE', 0, '0'... https://github.com/rails/rails/blob/6-1-stable/activemodel/lib/active_model/type/boolean.rb) will be saved as false in the ActiveRecord record (if the column type is boolean, of course). All other values (I think) will be saves as true

Knowing this is great, but when are those values actually "turned" to either true or false?

Is this comparable to any callback (e.g. before_validation)? In our case especially, can we make sure it runs before validations are run?

If anyone even finds where this is stated within the rails code, it would be awesome pointing to that :)

user_544825 · Answer

When you set a value in your model the setter will typecast the value:

class Thing
  include ActiveModel::Model
  include ActiveModel::Attributes
  attribute :awesome, :boolean
end

t = Thing.new
t.awesome = "1"
t.awesome # true

If you want to tap into the process the most straight forward way is by redefining the setter.

class Thing
  include ActiveModel::Model
  include ActiveModel::Attributes
  attribute :awesome, :boolean

  def awesome=(value)
    # do something
    super
  end
end

When you initialize, create or update a model from a Hash of attributes ActiveModel::AttributeAssignment handles setting the attributes from a hash by looping through the keys and values and calling the appropriate setter.

ActiveModel::Attributes is a previously private API that was exposed in Rails 5 and it forms the cornerstone of ActiveRecord::Attributes which is a more specialized implementation where the model is backed by a database table. In ActiveRecord::Attributes the typecasting is also done in the setter but it also includes stuff like dirty tracking and keeps track of attributes even before they are typecast. ActiveRecord::Attributes not only handles typecasting user input but it also handles typecasting values to and from the database.

ActiveRecord also includes a whole multitude of methods for assigning and updating methods that vary in if they fire callbacks or validations.

"Is this comparable to any callback (e.g. before_validation)? In our case especially, can we make sure it runs before validations are run?

This really depends on which method we are talking about. But in most cases the actual assignment happens before any callbacks are run.

See:

When do boolean fields transform to true/false in Rails?

1 Answers