For a Flutter application requiring complex queries and relationships in offline storage, what type of database would you recommend and why?

For a Flutter application with complex queries and relationships in offline storage, Hive would be a recommended database. Hive is a lightweight, NoSQL, and key-value store database specifically designed for Flutter. It excels in scenarios requiring efficient local storage with a simple API and fast performance. Hive is well-suited for Flutter apps with intricate data structures, offering a balance between simplicity and performance for offline data storage needs in complex applications.