How to Update an Object in an Array Using Mongoose in Node.js

Learn how to effectively update an array of objects in MongoDB using Mongoose, including a step-by-step guide and code examples.
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The Problem

Imagine we have a document from a Cart schema that looks like this:

[[See Video to Reveal this Text or Code Snippet]]

Our goal is to increase the quantity of the item uniquely identified by item_id = 101 and color = 'white'.

Attempted Solution

Initially, you might try to fetch the document, find the index of the item you want to update, and then modify the quantity directly. Here’s what that might look like:

[[See Video to Reveal this Text or Code Snippet]]

While this seems logical, you might find that the changes are not being saved. The reason for this issue is that Mongoose does not recognize any changes made to arrays directly. This results in the save() method not being invoked correctly.

The Solution

To resolve this problem, we need to inform Mongoose that the line_items array has been modified. We can do this by using the markModified() method. Here’s how you can implement this:

Updated Code

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Solution

Find the Index: We use findIndex() to locate the object in the line_items array that matches our criteria (item_id and color).

Modify the Quantity: We increase the quantity of the identified object.

Conclusion

Updating an object in an array within a MongoDB document using Mongoose requires a little extra care to ensure Mongoose detects the changes. By using the markModified() method, we can inform Mongoose about the changes we’ve made to array fields. This solution allows us to effectively manage complex data structures within our database.

With this knowledge in hand, you can confidently update nested documents in your MongoDB collections using Mongoose. Happy coding!