Java selectByPrimaryKey Method: Retrieve Database Records by Primary Key

The method 'selectByPrimaryKey' is used to retrieve a record from a database table based on its primary key. It is typically used when you want to retrieve a specific record from a table using its primary key value.

Here is an example of how the 'selectByPrimaryKey' method can be used:

public class UserDAO {
    public User selectByPrimaryKey(int id) {
        // Database connection and query execution code
        // ...
        
        // Example query using primary key
        String query = 'SELECT * FROM users WHERE id = ?';
        PreparedStatement statement = connection.prepareStatement(query);
        statement.setInt(1, id);
        
        ResultSet resultSet = statement.executeQuery();
        
        // Process the result set and create a User object
        User user = null;
        if (resultSet.next()) {
            int userId = resultSet.getInt('id');
            String username = resultSet.getString('username');
            // ...
            
            user = new User(userId, username);
        }
        
        // Close resources and return the User object
        resultSet.close();
        statement.close();
        
        return user;
    }
}

In this example, the 'selectByPrimaryKey' method takes an integer parameter 'id', which represents the primary key value of the user we want to retrieve. It then creates a SQL query using the primary key value and executes it using a prepared statement. The result set is processed to retrieve the necessary data and create a 'User' object. Finally, the method closes the resources and returns the 'User' object.

Note that the actual implementation of the 'selectByPrimaryKey' method may vary depending on the specific database and ORM (Object-Relational Mapping) framework being used.