How to clean Entity fields before saving

As kilishan has already mentioned you should define $allowedFields within you model that's handling the entity.
This performs array_intersect_keys against any given array or entity that your are trying to save/update or insert.

Basically if you have:

PHP Code:

$this->allowedFields = ['user_id']; 


And your incoming _POST array or keys in your Entity look similar to:

PHP Code:

[
    'random' => 'stuff',
    'bad' => 'things',
    'user_id' => 1,
    'get' => 'intersected'
] 


Then only 'user_id' from example above gets passed to database. Now here's the point that I just cannot stress enough:
Always declare $this->validationRules in your Model to make sure that keys that get passed: also get validated against expectations.

On the other hand: Maybe I got your question wrong and you wanted to know how can you Filter out keys that you can store in the $entity object itself?
If so here's a quick example to help anyone who's in need:

PHP Code:

<?php

class MyEntity
{
    public int $user_id = 0; 
    # Add more local keys with default values here ...

    # ...

    # This 'magic' method makes sure every time you set 
    # current entity's local value it must be pre-existing.
    public function __set(string $key, mixed $value): void
    {
        if (property_exists($this, $key)) {
            $this->$key = $value;
        }
    }

    # If you want to initiate entity with array of keys, ex:
    # new Entity\MyEntity(['user_id' => 8]);
    # then you would love to have a constructor like that:
    public function __construct(array $dataset = [])
    {
        if (! empty($dataset)) {
            foreach ($dataset as $key => $value) {
                # Set each key.
                $this->$key = $value;
            }
        }
    }
} 


Have fun!