**Course Title:** Qt 6 Application Development with C++ **Section Title:** Integrating Databases with Qt **Topic:** Performing CRUD operations (Create, Read, Update, Delete) **Overview** --------------- In the previous topic, we introduced you to SQL databases in Qt using QSqlDatabase. Now, we'll dive deeper into performing CRUD (Create, Read, Update, Delete) operations on a database. This topic will cover the essential concepts and techniques required to interact with a database using QSqlQuery and QSqlRecord. **Understanding CRUD Operations** ------------------------------- CRUD operations are the foundation of database interaction. They allow you to create new records, read existing records, update existing records, and delete records. | Operation | Description | | --- | --- | | Create | Insert new records into the database | | Read | Retrieve existing records from the database | | Update | Modify existing records in the database | | Delete | Delete existing records from the database | **Performing CRUD Operations with QSqlQuery** --------------------------------------------- To perform CRUD operations, we use QSqlQuery. This class provides a means of executing SQL queries on a database. ### Creating Records To create a new record, you can use the `INSERT INTO` statement with QSqlQuery. ```cpp QSqlQuery query; query.exec("INSERT INTO employees (name, age) VALUES ('John Doe', 30)"); ``` ### Reading Records To read existing records, you can use the `SELECT` statement with QSqlQuery. ```cpp QSqlQuery query; query.exec("SELECT * FROM employees"); while (query.next()) { QSqlRecord record = query.record(); // Process the record... } ``` ### Updating Records To update existing records, you can use the `UPDATE` statement with QSqlQuery. ```cpp QSqlQuery query; query.exec("UPDATE employees SET age = 31 WHERE name = 'John Doe'"); ``` ### Deleting Records To delete existing records, you can use the `DELETE` statement with QSqlQuery. ```cpp QSqlQuery query; query.exec("DELETE FROM employees WHERE name = 'John Doe'"); ``` **Using QSqlRecord to Manipulate Data** ----------------------------------------- QSqlRecord provides a convenient way to manipulate data in a database. You can use it to insert, update, and delete records. ```cpp QSqlRecord record; // Set the record values record.setGenerated("id"); record.setValue("name", "Jane Doe"); record.setValue("age", 25); // Insert the record QSqlQuery query; query.prepare("INSERT INTO employees (name, age) VALUES (:name, :age)"); query.bindValue(":name", record.value("name")); query.bindValue(":age", record.value("age")); query.exec(); // Retrieve the inserted record query.exec("SELECT * FROM employees WHERE name = 'Jane Doe'"); query.next(); ``` **Key Concepts and Takeaways** ----------------------------- * Understand the CRUD operations and how to perform them using QSqlQuery and QSqlRecord. * Use `INSERT INTO` to create new records, `SELECT` to read existing records, `UPDATE` to modify existing records, and `DELETE` to delete records. * Use strSqlQuery and QSqlRecord to manipulate data in a database. * Always validate and sanitize user input to prevent SQL injection attacks. **What's Next?** ----------------- In the next topic, we'll cover displaying database data using QTableView and QSqlTableModel. If you have any questions or concerns regarding this topic, feel free to ask in the comments below. **Additional Resources:** * Qt Documentation: [QSqlQuery](https://doc.qt.io/qt-5/qsqlquery.html) * Qt Documentation: [QSqlRecord](https://doc.qt.io/qt-5/qsqlrecord.html) **Code Examples:** * All code examples used in this topic are available in the [Qt 6 Application Development with C++ repository](https://github.com/Qt-6-App-Dev-Cpp). This concludes the topic on performing CRUD operations. In the next topic, we'll explore displaying database data using QTableView and QSqlTableModel.