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Query Object

Query Object pattern with example in PHP

In PHP, the Query Object pattern is a design pattern that separates the responsibility of querying data from the rest of the application logic. It helps in achieving better separation of concerns and improves code readability and maintainability.

The Query Object pattern’s fundamental concept is the creation of a separate class that represents a particular query. All the data and methods required to create and run the query are contained in this class. It offers a clearer, more expressive approach to interface with the database by abstracting away the specifics of the underlying database.

Let’s understand this concept through an example:
<?php
class UserQuery
{
private $dbConnection;
public function __construct(PDO $dbConnection)
{
$this->dbConnection = $dbConnection;
}
public function getUsersByRole($role)
{
$query = "SELECT * FROM users WHERE role = :role";
$statement = $this->dbConnection->prepare($query);
$statement->bindParam(':role', $role);
$statement->execute();
return $statement->fetchAll(PDO::FETCH_ASSOC);
}
}

In this example, we have a UserQuery class that encapsulates the logic for querying user data from the database. The class takes a PDO database connection object in its constructor, which allows it to interact with the database.

The getUsersByRole method is responsible for constructing and executing the query to retrieve users based on their role. It prepares the query with a placeholder :role and binds the $role parameter to it. Then, it executes the query and returns the result using the fetchAll method.

By using the Query Object pattern, we can separate the database-related code from the rest of the application logic. Other parts of the application can utilize the UserQuery class to perform user-related queries without having to deal with the specifics of querying the database.

// Example usage
<?php
$dbConnection = new PDO('mysql:host=localhost;dbname=sample_database', 'username', 'password');
$userQuery = new UserQuery($dbConnection);
$admins = $userQuery->getUsersByRole('admin');
$managers = $userQuery->getUsersByRole('staffmanager');

In this usage example, we create an instance of the UserQuery class, passing the database connection object to it. We then use the getUsersByRole method to retrieve users based on their roles, such as ‘admin‘ or ‘staffmanager’.
The Query Object pattern helps in centralizing and organizing database queries, making them more reusable and easier to manage. It also promotes better code organization and reduces duplication of query logic across different parts of the application.

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