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Discover how to solve the frustrating `DB locked` error in Flutter's SQFLite database by utilizing transactions properly and avoiding race conditions.
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This video is based on the question https://stackoverflow.com/q/62254316/ asked by the user 'Akshay' ( https://stackoverflow.com/u/2220092/ ) and on the answer https://stackoverflow.com/a/62257088/ provided by the user 'alextk' ( https://stackoverflow.com/u/563979/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the 'DB Locked' Issue in Flutter's SQFLite Database

Working with databases in Flutter can be a delightful experience, but it comes with its own set of challenges. One frustrating problem developers often encounter is the 'DB locked' error when using the SQFLite plugin. This error can halt your application and leave users in a lurch, especially if your app relies on real-time database interactions. In this post, we will break down the potential causes of the DB locked error in Flutter and explore effective solutions to keep your app running smoothly.

Understanding the Problem

In Flutter, using SQFLite to manage your SQLite databases can lead to issues when multiple operations try to access the database simultaneously. In the scenario described, the user is attempting to download new data daily, updating or inserting records as necessary. The error occurs even when transactions and batches are utilized correctly. It seems to stem from how database calls are handled during transactions, especially with read operations like getSongList() being called outside the transaction scope.

The Core Issue

Unexpected Database Access: The getSongList() function is called multiple times outside of the transaction context, which can lead to database access conflicts.

Missing Await on Batch Commit: Not awaiting the completion of a batch commit can cause subsequent operations to execute too quickly, potentially leading to access issues.

Race Conditions: When multiple asynchronous database operations occur without proper management, they can collide, causing the database to lock.

Solution Steps

Step 1: Pass Transaction Validity

One crucial adjustment is to ensure that all database operations within your transaction utilize the correct transaction instance. Instead of calling _database directly in your database functions, pass the txn parameter to your getSongList() call. Here’s how to modify your code:

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

Step 2: Update Your Transaction Calls

Make sure to replace calls to getSongList() in your transaction with the following:

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

This guarantees that all reads within the transaction are handled seamlessly without contention.

Step 3: Properly Await Batch Commit

The next significant change is to ensure you await the batch commit. Instead of letting it run independently, update your commit statement as follows:

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

This ensures the database is not accessed until all pending changes are fully committed, effectively reducing the risk of encountering a lock.

Step 4: Use pedantic Tools

Consider integrating the pedantic package into your project. This package can help catch potentially missing await statements and notify you of missing asynchronous handling, ultimately leading to more robust code.

Conclusion

Dealing with the 'DB locked' error in your Flutter SQFLite implementation doesn’t have to be a continuous struggle. By ensuring that your database operations are transactional and properly awaited, you can minimize lock occurrences. Remember to:

Adjust your getSongList() to accept transaction objects.

Always await your batch commits.

Consider using helpful libraries like pedantic to catch common errors.

By implementing these solutions, your app can run efficiently, ensuring smooth database operations while providing a better experience for your users. Happy coding!