31.9. Data persistence with SQLite in Flutter: Working with complex queries

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SQLite is an embedded relational database that is very easy to use and very powerful. It is widely used in mobile devices and small applications. In chapter 31.9 of our Flutter and Dart course, we'll cover data persistence with SQLite in Flutter and how to work with complex queries.

Before we get started, it's important to understand what SQLite is. SQLite is a SQL database engine that is embedded in an application. It does not require a separate server process, which makes it ideal for mobile applications where the database is stored locally on the device. SQLite is capable of handling complex queries, making it a great choice for applications that require a high level of data manipulation.

To start using SQLite in your Flutter app, you need to add the sqflite dependency to your pubspec.yaml file. sqflite is a Flutter plugin that provides a high-level interface to SQLite. It allows you to perform database operations such as creating tables, inserting data, querying data and much more.

Once the dependency is installed, you can start creating your database. In Flutter, this is done by creating a class that extends the DatabaseProvider class. This class will be responsible for opening the database, creating tables and executing queries.

To work with complex queries, SQLite offers a number of SQL operations that you can use. For example, you can use the WHERE clause to filter results, the JOIN clause to combine data from multiple tables, the GROUP BY clause to group results, and the ORDER BY clause to order results. You can also use SQL functions such as COUNT(), MAX(), MIN(), AVG() and SUM() to perform calculations on your data.

Let's take a look at an example of how you can use these operations in your Flutter app. Suppose you have a table called 'users' with columns 'id', 'name' and 'age'. You want to find all users who are 18+ and sort them by name. You can do this with the following query:

SELECT * FROM users WHERE age > 18 ORDER BY name;

This query will return all users who are 18+ and sort them by name. You can run this query in your Flutter app using sqflite's rawQuery() method:

var result = await db.rawQuery('SELECT * FROM users WHERE age > 18 ORDER BY name');

The result of this query will be a list of maps, where each map represents a row of the 'users' table.

More complex queries can involve multiple tables. For example, suppose you have a second table called 'orders' with columns 'id', 'user_id' and 'product'. You want to find all users who have ordered a certain product. You can do this with the following query:

SELECT users.* FROM users JOIN orders ON users.id = orders.user_id WHERE orders.product = 'Product Name';

This query will return all users who ordered the product 'Product Name'. You can run this query in your Flutter app in the same way as the previous query.

In short, SQLite is a powerful tool for persisting data in Flutter applications. It allows you to run complex queries, which is useful for applications that require a high level of data manipulation. With practice, you will be able to use SQLite to build more complex and robust Flutter applications.

Next page of the Free Ebook:

26431.10. Data Persistence with SQLite in Flutter: Data Migration