Question

Suppose I’m writing a blog app: My Posts Entity should have a createddate, modifieddate, name, and slug property (the slug would be generated when I call setName() for the Entity). I want to reuse this code, but I also want to reuse it on-demand. I may, for instance, have a Log Entity which wants to use createddate, but not modifieddate or slug functionality.

Class inheritance, whether via traits (mixins) or abstract classes, seems to be an insufficient, or at least improper, approach to reusing this functionality, as it doesn’t pass the is-a test. After all, the Entity has-a createddate, but isn’t a createddate itself.. so we should use Composition rather than Inheritance, right?. However, observer doesn’t seem to work here, since while I want to use this functionality on-demand, Doctrine’s use of annotation and object properties seem to make horizontal injection difficult (and expensive?) without use of Reflection.

To show some code and simplify the question a bit: can I at once inject the following definition and functionality into an Entity without breaking DRY or good OOP (proper use of composition / inheritance) practice?

/**
 * @var DateTime $createddate
 *
 * @ORM\Column(type="datetime")
 */
private $createddate;

/**
  * @ORM\PrePersist
  */
public function createddatePrePersist() {
    $this->createddate = new \DateTime('now');
}

Answer 1

My personal opinion is that you’re trying to find the nail for your hammer. You don’t have to use composition, inheritance, traits, or any OOP pattern for every entity.

I tend to consider that the creationDate is an inherent property of my entity, and any entity that requires a creation date has this property. One may argue that’s repeating myself, but in my opinion that makes the whole entity much easier to read.

Oh, and if I may, I wouldn’t use an ORM-specific method, which is not part of my domain model, to initialise the creation date. This would be done in my constructor:

/**
 * @var DateTime $createddate
 *
 * @ORM\Column(type="datetime")
 */
private $createddate;

public function __construct()
{
    $this->createddate = new \DateTime();
    // ... and other business rules that need to be enforced in the constructor
}