How to Make User UID Match Document ID in Firestore

Learn how to synchronize user UID with document ID in Firestore using Flutter and Firebase. This easy guide offers comprehensive steps and tips on maintaining user data integrity.
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Synchronizing User UID with Document ID in Firestore

In the world of app development, maintaining consistency between user data in Firebase Authentication and Cloud Firestore is crucial. Many developers face a common dilemma: how to ensure that the User ID (UID) from Firebase Authentication matches the document ID for users in Firestore. This article will walk you through the solution on how to achieve this synchronization effectively by leveraging the has features provided by Firebase and Flutter.

The Problem

When users sign up to your app, Firebase Authentication generates a unique identifier (UID) for each user. Meanwhile, Cloud Firestore stores user details and information as documents in collections. To maintain a well-structured database, you want the document ID for each user's information in Firestore to match the UID created in Firebase Authentication. This creates a single source of truth for user data, making it easier to manage and query.

Example Scenario

User Info from Authentication:

UID: U8EZAjrCWQRvll6CVmI6OpGZwcH3

Firestore Document Structure:

User collection with documents representing each user.

The goal is to have the document for this user in Firestore have the same ID as their Firebase UID.

The Solution

Step 1: Modify User Creation Logic

To set the document ID to the user's UID, you need to make a small adjustment to the function that creates new user documents. Instead of using the add() method—which automatically generates a unique ID for each document—you should use the set() method to specify the document ID manually. Here’s how you can implement this:

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

In the code block above, userId represents the UID of the newly created user. This will ensure that the document ID in Firestore directly corresponds to their UID.

Step 2: Implement Safeguards

While the above method directly addresses the ID synchronization, it's essential to consider the security and scalability of your data management. Therefore, rather than allowing direct write access to your user collection from the client-side, you can manage user data on the server-side through Firebase Cloud Functions. For example, using Firebase Authentication triggers can automate the process of adding, modifying, or deleting user data whenever a user account is created or altered.

Example Code for User Creation

Here's an overview of how your overall user creation process might look like, incorporating UID synchronization:

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

This logic ensures your app creates a user in both Firebase and Firestore while maintaining a clean mapping between user records.

Conclusion

Synchronizing your user’s UID with their document ID in Firestore simplifies data management and reinforces a clear, organized database structure. By using the set() method within your Firestore operations, you can easily keep these identifiers aligned. Remember, good practices such as managing this data on the server-side should be incorporated to enhance security and maintainability.

Implementing this approach will provide a smoother development experience and improve application efficiency. Happy coding!