forbid to create champ with same type_de_champ and same row

app/models/champ.rb

@@ -21,6 +21,8 @@ class Champ < ApplicationRecord
 
   before_create :set_dossier_id, if: :needs_dossier_id?
 
+  validates :type_de_champ_id, uniqueness: { scope: [:dossier_id, :row] }
+
   def public?
     !private?
   end

spec/models/champ_spec.rb

@@ -3,6 +3,16 @@ describe Champ do
 
   it_should_behave_like "champ_spec"
 
+  describe "validations" do
+    let(:row) { 1 }
+    let(:champ) { create(:champ, type_de_champ: create(:type_de_champ), row: row) }
+    let(:champ2) { build(:champ, type_de_champ: champ.type_de_champ, row: champ.row, dossier: champ.dossier) }
+
+    it "returns false when champ with same type_de_champ and row already exist" do
+      expect(champ2).not_to be_valid
+    end
+  end
+
   describe '#public?' do
     let(:type_de_champ) { build(:type_de_champ) }
     let(:champ) { type_de_champ.champ.build }