How Can I Access Global Variables Within a PHP Class Without Errors?

Accessing Global Variables Within a Class

Introduction

The quandary of accessing global variables from within a class is a common challenge encountered in object-oriented programming. This article addresses the issue specifically in PHP, providing alternative solutions to the "Call to a member function query() on a non-object" error.

The Problem

In the provided code snippet, the fatal error arises from the attempt to call the query() method on the $db variable within the get_records() method of the pagi class. The root cause is the lack of an established connection between the class and the global $db object.

Alternative Solutions

1. Dependency Injection

Dependency injection is a design pattern that involves passing the required objects as parameters to the class. In this case, the database connection object (i.e., $db) would be injected into the constructor of the pagi class. This method ensures that the class has access to the global variable without resorting to global scope.

2. Method Parameter Injection

Alternatively, the database connection object can be passed as a parameter to the get_records() method itself. While this method does not necessarily improve encapsulation, it allows for greater flexibility in managing dependencies.

Benefits of Dependency Injection

1. Loose Coupling:

Dependency injection promotes loose coupling between classes, making it easier to swap out dependencies as needed. In this scenario, it would be straightforward to switch to a different database connection without modifying the code of the pagi class.

2. Unit Testing:

By passing dependencies through parameters, unit tests can be conducted more efficiently. Instead of testing multiple classes simultaneously, only the specific unit (in this case, the pagi class) is tested.

Conclusion

Both dependency injection and method parameter injection offer viable solutions to accessing global variables within a class. The choice between the two approaches depends on the specific design requirements of the application. Ultimately, both methods aim to maintain encapsulation while providing access to necessary external resources.

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