Resolving the Issue of addToSet with Multiple Arrays in MongoDB Operations

Learn how to handle multiple `$addToSet` operations correctly in a MongoDB update to ensure all arrays are updated properly without overwriting.
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Resolving the Issue of addToSet with Multiple Arrays in MongoDB Operations

When working with MongoDB and Mongoose, developers often encounter various challenges while updating documents. One common issue arises when trying to use multiple $addToSet operations to update several arrays in a single database operation. If you’ve been struggling with this problem, you’re not alone. In this post, we'll explore why this issue occurs and how to fix it effectively.

The Problem: Understanding $addToSet Behavior

Here’s a brief overview of your situation. You have a user document with multiple fields, specifically arrays for androidIds, advertisingIds, and firebaseInstallationIds. You attempt to use the $addToSet operator to add values to these arrays, but you notice only the last array (in this case, firebaseInstallationIds) ends up being set. Why does this happen?

The Reason Behind the Issue

The problem stems from how JavaScript handles object properties. When you define an object with multiple properties having the same key, the last property will override the earlier ones. In your case:

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

This code structure leads to only firebaseInstallationIds being considered for the update since it’s the last $addToSet operation, effectively ignoring the previous ones.

The Solution: Combining $addToSet Operations

To resolve this issue, you must merge all $addToSet operations into a single object. Here’s how to adjust your code accordingly:

Working Example

Below is the corrected version of your user update operation:

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

Key Changes Made

Combined all $addToSet updates into a single object: Now, all specified IDs will be added to their respective arrays without being overwritten.

Kept the $set operation intact to ensure the token assignment remains functional.

Conclusion: Simplifying Your MongoDB Update Operations

By following the solution provided, you can ensure that all your array fields are updated correctly in a single operation without any loss of data. Remember, when working with MongoDB and Mongoose, keeping your operations organized and understanding how JavaScript objects function will save you from common pitfalls.

If you have further questions or encounter other challenges while using Mongoose or MongoDB, feel free to reach out!