**Course Title:** PyQt6 Application Development **Section Title:** Integrating Databases with PyQt6 **Topic:** Working with QSqlDatabase and QSqlQuery **Overview** In this topic, we will delve into the world of database integration in PyQt6 using the `QSqlDatabase` and `QSqlQuery` classes. These classes provide a convenient and efficient way to interact with various types of databases, including MySQL, PostgreSQL, and SQLite. We will explore how to establish connections, execute SQL queries, and retrieve results. **What You Will Learn** * How to create a `QSqlDatabase` object and connect to a database * How to use `QSqlQuery` to execute SQL queries * How to retrieve results from a query * How to handle errors and exceptions **Creating a QSqlDatabase Object** To start working with databases in PyQt6, you need to create a `QSqlDatabase` object. This object represents the database connection and provides a set of methods for interacting with the database. Here's an example of how to create a `QSqlDatabase` object for a SQLite database: ```python import sys from PyQt6.QtSql import QSqlDatabase, QSqlQuery from PyQt6.QtCore import QSqlDatabase as DB # Create a QSqlDatabase object for a SQLite database db = QSqlDatabase.addDatabase(DB.DriverName.SQLite) db.setHostName("localhost") db.setDatabaseName("mydatabase.db") ``` In this example, we first import the necessary modules. We then create a `QSqlDatabase` object using the `addDatabase()` method, specifying the database type (in this case, SQLite) and the host name (localhost). **Connecting to a Database** Once you have created a `QSqlDatabase` object, you need to connect to the database using the `open()` method: ```python # Open the database connection if db.open(): print("Database connection established") else: print("Error connecting to database:", db.lastError().databaseText()) sys.exit(1) ``` In this example, we use the `open()` method to establish the database connection. If the connection is successful, we print a success message. Otherwise, we print an error message with the database error text using the `lastError()` method. **Using QSqlQuery to Execute SQL Queries** To execute SQL queries, you can use the `QSqlQuery` class. This class provides a set of methods for executing queries, retrieving results, and handling errors. Here's an example of how to use `QSqlQuery` to execute a SQL query: ```python # Create a QSqlQuery object query = QSqlQuery(db) # Execute a SQL query query.exec_("SELECT * FROM mytable") # Retrieve the results while query.next(): print(query.value(0), query.value(1), query.value(2)) ``` In this example, we create a `QSqlQuery` object and execute a SQL query using the `exec_()` method. We then retrieve the results using the `next()` and `value()` methods. **Handling Errors and Exceptions** When working with databases, errors can occur due to various reasons such as invalid SQL syntax, database connectivity issues, or permission errors. To handle errors, you can use the `lastError()` method of the `QSqlDatabase` object: ```python # Check for errors error = db.lastError() if error.isValid(): print("Error:", error.databaseText()) ``` In this example, we use the `lastError()` method to retrieve the last error that occurred. If the error is valid, we print an error message with the database error text. **Practical Takeaways** * Use the `QSqlDatabase` class to establish a database connection * Use the `QSqlQuery` class to execute SQL queries and retrieve results * Use the `lastError()` method to handle errors and exceptions * Always check for errors and handle them accordingly **What's Next** In the next topic, we will cover performing CRUD (Create, Read, Update, Delete) operations in SQL databases using PyQt6. Do you have any questions or need help with the material covered so far? Leave a comment below, and we'll be happy to assist you.