How to Save Firestore Data in Shared Preference: A Complete Guide to Fixing the '[]' Operator Error

Discover how to effectively save data from Firestore to shared preferences in Flutter while overcoming the common '[]' operator error in DocumentSnapshot.
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This video is based on the question https://stackoverflow.com/q/63754888/ asked by the user 'Tarun Binwal' ( https://stackoverflow.com/u/7474406/ ) and on the answer https://stackoverflow.com/a/63754963/ provided by the user 'Morez' ( https://stackoverflow.com/u/12828249/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Save Firestore Data in Shared Preference: A Complete Guide to Fixing the '[]' Operator Error

Are you facing issues while trying to save Firestore data into local storage using shared preferences in your Flutter application? If you’ve encountered the error message "The operator '[]' isn't defined for the type 'DocumentSnapshot'", you are not alone. This is a common issue among Flutter developers, especially those who are new to Firebase and the Dart programming language. In this guide, we’ll explore the problem and provide a detailed solution.

Understanding the Problem

When you attempt to access the data in a DocumentSnapshot returned from Firestore with the bracket operator [], you may encounter the mentioned error. This occurs because the DocumentSnapshot class does not support this operator natively. Instead, you should utilize the data() method to retrieve the data stored within a document.

Common Scenario

When users try to retrieve their data from Firestore, they often do so with code like this:

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

This line will trigger an error because documents[0] is a DocumentSnapshot, not a regular map. To successfully retrieve the data, you need a different approach.

The Solution

To solve this problem, we need to update our code to correctly retrieve the Firestore data and save it into shared preferences. Here’s how to do it step-by-step:

Step 1: Sign in Using Google Authentication

Make sure you sign in using Google authentication properly. Here is the code snippet for that:

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

Step 2: Check If User Exists in Firestore

Next, you need to check if the user already exists in the Firestore database:

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

Step 3: Handle New and Existing Users

If the user is new, store their information in Firestore and save the user data into shared preferences.

If the user already exists, retrieve and save the user's data from Firestore using the data() method:

Code for New User

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

Code for Existing User

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

Step 4: Conclusion

In conclusion, to effectively save Firestore data in shared preferences while avoiding the DocumentSnapshot error, always remember to use the data() method to access the document's contents. By following the above steps, you should be able to implement the functionality correctly without running into errors.

Now that you have the solution, go ahead and integrate it into your Flutter app! Happy coding!