db: add uniqueness constraints to Etablissement

db/migrate/20210722133553_add_unique_index_to_etablissement.rb

@@ -0,0 +1,16 @@
+class AddUniqueIndexToEtablissement < ActiveRecord::Migration[6.1]
+  include Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    delete_duplicates :etablissements, [:dossier_id]
+    remove_index :etablissements, [:dossier_id]
+    add_concurrent_index :etablissements, [:dossier_id], unique: true
+  end
+
+  def down
+    remove_index :etablissements, [:dossier_id]
+    add_concurrent_index :etablissements, [:dossier_id]
+  end
+end