A design pattern solves a specific problem. It is not a tool; it is just a description or template that describes how to solve a specific problem. Design patterns are important, and they play a good role in writing clean and clear code.

One of the most widely used design patterns in the PHP community is the Model View Controller (MVC) pattern. Most PHP frameworks are built upon this pattern. MVC advises you to keep the business logic and data operations (that is, the model) separate from the presentation (the view). Controllers just play the role of a middleman between models and views and make the communication between them possible. There is no direct communication between models and views. If a view needs any kind of data, it sends a request to the controller. The controller knows how to operate on this request and, if needed, make a call to the model to perform any operation on the data (fetch, insert, validate, delete, and so on). Then at last, the controller sends a response to the view.

In best practices, fat models and skinny controllers are used. This means that controllers are only used to take a specific action on a request and nothing else. Even in some modern frameworks, the validation is moved out of the controllers and is performed at the model level. These models perform all the operations on the data. In modern frameworks, models are considered as a layer, which can have multiple parts, such as the business logic, Create Read Update Delete (CRUD) database operations, data mapper pattern and services, and so on. So, a full load of models and controllers is just sitting there and enjoying the lazy work load.

Another widely used design pattern is the factory design pattern. This pattern simply creates objects that are needed to be used. Another good pattern is the observer pattern, in which an object calls different observers on a specific event or task on it. This is mainly used for event handling. Yet another widely used pattern is the singleton pattern, which is used when there is a requirement that only a single object of a class be used throughout the application's execution. A singleton object can't be serialized and cloned.