Ljubljana, Slovenia

API development methodology

  • I needed a way to create and connect only to those services I actually need to run. If I only need to connect to Redis, I don’t need to connect to MySQL as well.
  • Leverage PHP language constructs to this end. Injecting dependencies should be language driven, not programmer driven.

I want you to think about this. Language driven vs. programmer driven - this is the main point. When it comes to programmer driven dependency injection, it will happen that your programmer(s) will be using their time writing methods that will get, set and report missing dependencies. It is a flawed concept from the beginning, as it introduces human error into the equation. The programmer can and will forget to pass a dependency into an object causing a fatal error which doesn’t trigger an exception that could be caught. The problems mount - the programmer requires attention to detail and discipline, and uses his time writing boiler plate code instead of developing new features. You can reduce this risk by implementing your dependencies as language driven constructs. PHP 5.4 introduced traits that could be leveraged to infer dependencies to be injected into objects, after they are instantiated. A typical execution flow would then be:

  • Instantiate the API request object
  • Instantiate and inject required dependencies based on used traits
  • Execute the API request

Injecting traits would be done by listing all traits used in an object using Reflection. Depending on which traits are used, the developer defines only once how to inject this dependency into the object. Injecting multiple dependencies is then just as simple as using additional traits for them. Take a look at my approach here (github gist): DependencyInjectionWithTraits.php There is some room for improvements, especially when it comes to trait definitions and instantiating the dependencies. But when it comes to writing your own “Petstore” and “BiggerPetstore” the benefit is immediately apparent. The programmer uses his time to implement functionality instead of dealing with less subtle / ubiquitous dependency injection patterns. One could implement a more java-like dependency injector using ReflectionClass / ReflectionMethod functionality, parsing DocBook code comments for annotations and then inject fine grained dependencies, but that approach wouldn’t be any better. It would be much longer than the 40 lines needed for this example, and it wouldn’t add any additional functionality either. Pick your battles. - Tit Petric

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