PHPMD and Coupling Between Object classes (CBO)

Question

I'm working on a Magento 2 CRUD functionality following the best practices (best described here). On the project I'm working on we are using PHPMD (php mess detector). Among other rules, we have the CBO limit set to 13 (which I understand is the default). My repository is implementing the get, save, getList, delete, deleteById methods and the limit is already 12.

What would be best practice if I need to add other methods to this repository without overlapping the PHPMD CBO limit?

P.S. I think this can be the case for implementations in other frameworks/platforms as well, not strictly related to Magento 2.

Interface per method, implementation per interface. This is called SRP from the SOLID. This is a great rule. Prevents people from creating monstrous god classes. — Mike Doe, Jun 05 '19 at 19:23
can you please elaborate on this (maybe add an answer to the question if you need more room for the explanation). I would be really interested in an example if I'm not asking too much! — Radu, Jun 05 '19 at 19:25

score 2 · Accepted Answer · answered Jun 05 '19 at 19:39

This is one of the greatest rules that helps to keep your classes focused and easier to maintain. How many times have you seen that:

class XXXRepository
{
    public function findOneByCode($code);
    public function findOneByParams($params);
    public function findAllByParams($params);
    public function findActive($params);
    public function findForProductList($params);
    ... 5000 lines of spaghetti
}

Instead go for this, embrace interfaces, make your application depend upon abstractions, not implementation details:

interface ProductByCode
{
    public function findByCode(string $code): ?Product;
}

interface ProductsByName
{
    public function findByName(string $name): array;
}

Using the Dependency Injection component you can alias an interface to its implementation. Go for implementation per each interface. You can make use of a abstract class which will help you communicate with the persistence layer via the framework of your choice.

final class ProductByCodeRepository extends BaseRepository implements ProductByCode
{
    public function findByCode(string $code): ?Product
    {
        return $this->findOneBy(['code' => $code]);
    }
}

Interesting idea! However, isn't it there a risk to reach a point where you end up with too many files (which in a certain amount for big projects may become an issue) or too many dependencies to inject (in SonarQube for example you may have limits defined for the number of dependencies injected => in a CI/CD scenario your build won't pass)? I will research and try this and get back. — Radu, Jun 05 '19 at 20:00
Define “too many files”. Another thing is if you have a class which has more than 3 to 5 dependencies it’s for sure violating the SRP principle as well. Check out its cyclomatic complexity. — Mike Doe, Jun 05 '19 at 20:14
too many files .. I don't know classes times number of methods .. 200? I don't know .. Anyway, it looks like I definitely need to invest some time in researching SRP. I will get back! Thanks! — Radu, Jun 05 '19 at 20:20

PHPMD and Coupling Between Object classes (CBO)

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