In my system, I have the following resources:

defmodule Core.Feedbacks.Student do
  relationships do
    alias Core.Feedbacks

    has_many :feedbacks, Feedbacks.Feedback

    many_to_many :classes, Feedbacks.Class do
      through Feedbacks.StudentClass
      join_relationship :student_classes

      source_attribute_on_join_resource :student_id
      destination_attribute_on_join_resource :class_id
    end
  end
end

defmodule Core.Feedbacks.Class do
  relationships do
    alias Core.Feedbacks

    has_many :feedbacks, Feedbacks.Feedback

    many_to_many :students, Feedbacks.Student do
      through Feedbacks.StudentClass

      source_attribute_on_join_resource :class_id
      destination_attribute_on_join_resource :student_id
    end
  end
end

defmodule Core.Feedbacks.StudentClass do
  relationships do
    alias Core.Feedbacks.{Student, Class}

    belongs_to :student, Student do
      primary_key? true
      allow_nil? false
      attribute_writable? true
    end

    belongs_to :class, Class do
      primary_key? true
      allow_nil? false
      attribute_writable? true
    end
  end
end

defmodule Core.Feedbacks.Feedback do
  relationships do
    alias Core.Feedbacks

    belongs_to :student, Feedbacks.Student do
      allow_nil? false
      attribute_writable? true
    end

    belongs_to :class, Feedbacks.Class do
      allow_nil? false
      attribute_writable? true
    end
  end
end

As you can see, the Student resource has a many_to_many relationship with the Class resource and both resources have a has_many relationship with the Feedback resource.

I wan´t to create an aggregate that will tell me how many feedbacks a student has inside a class.

If I just wanted all the student feedbacks, an aggregate like this in my Student resource would work just fine:

count :total_feedbacks, :feedbacks

But I want to count all the feedbacks that are from that student and from an specific class, meaning that I would to, somehow, pass an :class_id argument to inside that count aggregate filter expression.

I’m not sure how to solve that using aggregates