Mongoose Relationships Updating Embedded Subdocuments

Learning Objective: By the end of this lesson, students will be able to update embedded subdocuments by id in Mongoose.

Updating subdocuments

There are a few approaches to updating subdocuments in Mongoose. The most straightforward approach involves the following steps:

1. Find the parent document.
2. Locate the desired subdocument within the parent.
3. Modify the properties of the subdocument.
4. Save the parent document to apply the changes.

Here’s an example of this process in action:

// Find the parent:
const todo = await Todo.findById(todoId);

// Locate the subdocument within the parent:
const subtask = todo.subtasks.id(subtaskId);

// Update the subdocument by marking it complete
subtask.isComplete = true;

// Save the parent document to persist changes:
await todo.save();

In the code snippet above, we modify the isComplete property of a subdocument like we would a typical JavaScript object. After updating the subdocument, calling save() on the parent ensures the changes are reflected in the database.

Implementing an update

To demonstrate the process in more detail, let’s create a function to update a subdocument.

Add the following function to queries.js at the bottom of the Query Functions section:

const updateSubtask = async () => {
  const todoId = '657b25adc8146427465857d7';
  const subtaskId = '6580677cf30bfef697ae046f';

  const todo = await Todo.findById(todoId);
  const subtask = todo.subtasks.id(subtaskId);

  subtask.isComplete = true;
  await todo.save();

  console.log('Updated document:', todo);
};

🚨 Make sure to replace todoId and subtaskId with actual ObjectIds from your database.

Next, call updateSubtask with the runQueries function:

const runQueries = async () => {
  console.log('Queries running.');
  await updateSubtask();
};

Run the queries.js file with the following command:

node queries.js

You should see a similar output in your terminal:

Updated document: {
  _id: new ObjectId('657b25adc8146427465857d7'),
  text: 'Learn React',
  isComplete: false,
  __v: 1,
  subtasks: [
    {
      text: 'Learn how props work',
      isComplete: true,
      _id: new ObjectId('6580677cf30bfef697ae046f')
    }
  ]
}