Bdtjtk

I want to validate that the set of associations for an instance are unique to all other instances, and if it is not unique I want it to be invalid.

In this case, I am working with a many_to_many relationship, so, an Exercise has many elements, and elements can have many Exercises. So I would like each exercise to have a unique set of elements so an exercise can have as many element associations as possible, but never have the same combination of elements as another exercise.

I've tried adding a custom validation to the join model but that doesn't work when I submit a lot of revised associations at one time (such as when I am editing associations through a nested form)

I've also tried putting the validation in the Exercise model by comparing the associations of the created or updated exercise against all other exercise element association sets that exist, but that doesn't seem to work because the associations aren't created until after I need to validate them. So it seems I need the associations built in order to validate their uniqueness, but once they're built it's already too late.

class Exercise < ApplicationRecord

  has_many :exercise_elements, dependent: :destroy

  has_many :elements, through: :exercise_elements

  accepts_nested_attributes_for :exercise_elements, allow_destroy: true

  validate :element_uniqueness, if: :elements_unique?, on: :update



  def elements_unique?

    all_exercises_but_self = Exercise.where.not(id: self.id)

    all_exercises = all_exercises_but_self.map(&:elements)

    all_sorted = all_exercises.each.sort

    this_exercise = self.elements.sort

    all_sorted.include?(this_exercise) ? true : false

  end



  def element_uniqueness

    if elements_unique?

      self.errors[:base] << "Exercise already exists, consider adding 

      different elements"

    end

  end

end



class ExerciseElement < ApplicationRecord

  belongs_to :exercise

  belongs_to :element

end



class Element < ApplicationRecord

  belongs_to :element_category

  has_many :exercise_elements

  has_many :exercises, through: :exercise_elements

end

I would expect

exercise1 = Exercise.create

exercise1.elements.push([Element.find(1), Element.find(2)])

exercise1.valid? > true



exercise2 = Exercise.create

exercise2.elements << Element.find(2)

exercise2.valid? > true

exercise2.elements << Element.find(1)

exercise2.valid? > false # invalid because associated elements are not a 

                         # unique set

                         # because exercise2.elements == exercise1.elements