Save submission alongside structured error

db/migrate/20180130101645_add_submission_to_structured_errors.rb

@@ -0,0 +1,5 @@
+class AddSubmissionToStructuredErrors < ActiveRecord::Migration
+  def change
+    add_reference :structured_errors, :submission, index: true
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20171120153705) do
+ActiveRecord::Schema.define(version: 20180130101645) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -305,8 +305,11 @@ ActiveRecord::Schema.define(version: 20171120153705) do
     t.integer  "file_id"
     t.datetime "created_at",        null: false
     t.datetime "updated_at",        null: false
+    t.integer  "submission_id"
   end
 
+  add_index "structured_errors", ["submission_id"], name: "index_structured_errors_on_submission_id", using: :btree
+
   create_table "submissions", force: :cascade do |t|
     t.integer  "exercise_id"
     t.float    "score"