majiayu000 PHP Design Patterns
Before writing code
Fetch live docs: Web-search php design patterns examples for current community patterns and best practices. For Magento-specific patterns, web-search site:developer.adobe.com commerce php development components.
Creational Patterns
Factory
Creates objects without exposing instantiation logic. In Magento, auto-generated Factory classes (SomeModelFactory) create non-injectable objects via $factory->create().
When to use: When you need new instances (entities, models) rather than shared singletons. When the caller shouldn't know the concrete class.
Builder
Constructs complex objects step by step. Magento's SearchCriteriaBuilder, FilterBuilder, SortOrderBuilder follow this pattern.
When to use: When object construction requires many optional parameters or multi-step assembly.
Singleton (Shared Instance)
Single instance shared across the application. Magento's Object Manager shares instances by default. Explicit singleton is generally an anti-pattern — prefer DI container sharing.
When to use: Rarely — let the DI container manage instance sharing.
Structural Patterns
Proxy
Delays instantiation of resource-intensive dependencies. Magento auto-generates Proxy classes (SomeClass\Proxy) that create the real object only when a method is called.
When to use: When a class injects a heavy dependency it doesn't always use.
Decorator
Wraps an object to add behavior without modifying the original. Used in Magento composite components and cache decorators.
When to use: When you need to add behavior to an object dynamically without subclassing.
Composite
Treats individual objects and compositions uniformly. Magento's UI component tree and layout container system follow this pattern.
When to use: When you have tree-structured data or components.
Behavioral Patterns
Strategy
Defines a family of algorithms, encapsulates each one, makes them interchangeable. Magento shipping carriers and payment methods are strategy implementations.
When to use: When you have multiple algorithms for the same task and want runtime selection.
Observer
Defines a one-to-many dependency. When one object changes state, all dependents are notified. Magento's event/observer system is a direct implementation.
When to use: When changes in one object should trigger actions in others without tight coupling.
Repository
Mediates between domain and data mapping layers. Magento's repository interfaces (ProductRepositoryInterface) centralize all data access through a clean API.
When to use: Always — for any data access beyond simple reads. It's the standard Magento pattern.
Command
Encapsulates a request as an object. Magento's Payment Gateway Command pattern uses this — authorize, capture, refund are separate command objects.
When to use: When you need to parameterize, queue, or log requests.
Architectural Patterns
Dependency Injection
Objects receive their dependencies through constructors rather than creating them. Magento's DI container (Object Manager + di.xml) is the foundation of the entire framework.
When to use: Always — it's the core pattern. Inject interfaces, not concrete classes.
Service Layer
Defines an application's boundary with a layer of services that encapsulates business logic. Magento's Service Contracts (interfaces in Api/) form this layer.
When to use: Always — expose module functionality through service interfaces.
Data Transfer Object (DTO)
Simple objects that carry data between processes. Magento's Data Interfaces (Api/Data/) are DTOs — they have getters/setters but no business logic.
When to use: When passing data across architectural boundaries (API, service layer).
Anti-Patterns to Avoid
- God Object — classes that do too much (split into focused services)
- Service Locator — calling Object Manager directly (use constructor injection)
- Anemic Domain Model — models with only getters/setters (add behavior where appropriate)
- Tight Coupling — depending on concrete classes (depend on interfaces)
- Hard-coded Dependencies — instantiating with
new(use factories or DI)
Best Practices
- Program to interfaces, not implementations
- Favor composition over inheritance
- Keep classes focused (Single Responsibility)
- Use DI container for dependency management
- Use factories for creating non-shared instances
- Use proxies for lazy-loading expensive dependencies
- Use the strategy pattern for swappable algorithms
- Document which pattern a class implements
Fetch current framework documentation for exact interface signatures and implementation patterns before applying.