class Missions_user <ActiveRecord:: Base

    validates :mission_id, presence: true

    validates :user_id, presence: true

    validate :mission_exist, on: :create

    validate :user_exist, on: :create

     private 

        def mission_exist

            mission = Mission.find_by(id: mission_id)

            if mission == nil

                errors[:mission] = "mission belong to Missions_user is not exist"

            end

        end

        def user_exist

            user =  User.find_by(id: user_id)

            if user == nil

                errors[:user] = "user belong to Missions_user is not exist"

            end

        end

end