refactoring

models/Todo.js

@@ -1,5 +1,6 @@
 const mongoose = require('mongoose');
 
+const TodoList = mongoose.model('TodoList');
 const { Schema } = mongoose;
 
 const TodoSchema = Schema({
@@ -11,4 +12,16 @@ const TodoSchema = Schema({
   completed: { type: Boolean, default: false },
 });
 
+TodoSchema.pre('save', async function () {
+  const list = await TodoList.findById(this.list);
+  list.todos.push(this.id);
+  await list.save();
+});
+
+TodoSchema.pre('remove', async function () {
+  const list = await TodoList.findById(this.list);
+  list.todos.remove(this.id);
+  await list.save();
+});
+
 mongoose.model('Todo', TodoSchema);