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Learn how to successfully update an array in Firestore using the `arrayUnion` method, avoiding common errors that can occur when mixing SDKs.
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Updating an Array in Firestore using arrayUnion

When working with Firebase Firestore, you might encounter a common problem: trying to update an array in your Firestore collection using the arrayUnion() method, only to be met with frustrating errors. One such error is:

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

This error can be especially confusing if you're just starting with Firestore or if your array is empty. Let's dive into a clear, step-by-step explanation to solve this problem.

Understanding the Problem

The main issue here arises from confusion between the Firestore Client SDK and the Firebase Admin SDK. Each SDK has its own API, and mixing them can lead to errors and unexpected behavior when performing operations like updating arrays.

The Setup

In the initial code snippet provided, the following code is used:

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

In this setup, the array players is intended to be updated with the userId without overwriting the existing data in the array.

The Real Issue: Mixing SDKs

Client vs. Admin SDKs

Client SDK: Intended to be used in client-side applications (e.g., web, mobile). It has its own set of methods for Firestore operations.

Admin SDK: Designed to be used in trusted server environments. It allows for administrative functions on your Firestore database, bypassing many of the security rules applied to client SDKs.

Why the Error Occurs

In your code, you are mixing up the FieldValue from the Admin SDK with operations meant for the Client SDK. This is where the conflict arises.

The client SDK's update method cannot handle a FieldValue from the Admin SDK properly, leading to the error mentioned.

Solution: Stick to One SDK

To resolve this issue, you should decide to use either the Admin SDK or the Client SDK, but not both in the same operation.

Recommended Approach

If you're operating on a Node.js backend (as in your provided example), it's recommended to use the Admin SDK. Here’s a corrected version of your code:

Use Admin SDK for Updates:
Make sure you import and initialize only the Admin SDK:

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

Update with arrayUnion:
Use arrayUnion properly as follows:

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

By ensuring you're using the Admin SDK throughout your backend code, you can avoid crossing paths with the Client SDK and thus eliminate the potential for these types of errors.

Conclusion

Updating arrays in Firestore with the arrayUnion method can lead to confusions if you're not careful with the SDKs being used. By adhering strictly to the Admin SDK for your server-side operations, you'll be able to manage your Firestore documents without running into problems like "unsupported field values."

Remember, when in doubt:

Stick to one SDK per context (Client or Admin).

Review the Firestore documentation and ensure you're familiar with the API being used.

With these guidelines, you should now be well on your way to successfully updating arrays in Firestore! If you encounter further issues or have questions, feel free to reach out to the community or explore more resources.