Add an additional field to associated GraphQL field return type

I have this GraphQL type in my application.

module Types
  module MyApp
    class MembersStatus < Types::Base::Object
      field :active, [Types::MyApp::User], null: true
      field :on_leave, [Types::MyApp::User], null: true
      field :status_unknown, [Types::MyApp::User], null: true
    end
  end
end

I want to add an additional field to the associated User Type for the on_leave field.

For example, for the on_leave field, I want to have the associated User to have an additional field leave_duration

field :leave_duration, Integer, null: true

So that, I can make queries like below:

query memberStatus{
  memberStatus {
    active { name }
    onLeave { name leaveDuration }
    statusUnknown { name } 
  }
}

I have looked into https://graphql-ruby.org/type_definitions/extensions.html#customizing-fields this doc but can't implement it yet. Can this be done? Please help.

Just as you described, you need to add the leave_duration field to the user type.

module Types
  module MyApp
    class UserType
      # other stuff
      field :leave_duration, GraphQL::Types::ISO8601Date, null: true

      # Optional: Define leave_duration if it isn't already a field on the model:
      def leave_duration
        # implementation that returns a date
      end
    end
  end
end

It looks like you may have had a typo in the field() call, where :leave_duration should be a symbol, not a variable or method. That is fixed in the above snippet.

Edit: Regarding your question about conditionally having leave_duration only when on_leave, I would suggest this:

def leave_duration
  return nil unless object.on_leave

  # implementation that returns a date
end

There is a way to hide the field from the schema, which is described here: https://github.com/rmosolgo/graphql-ruby/issues/893

But it seems way too overkill to me to hide a field based on the presence of another field. I think this is mainly intended to hide fields like is_admin for non-admin users.