UniqueCategoryId.php

<?php

namespace App\Rules;

use App\Entry;
use Illuminate\Contracts\Validation\Rule;

/**
 * Class UniqueCategoryId
 *
 * Rule to verify whether an in-category-id is unique, that is, it fulfills the following requirements:
 *
 * No entry with the same category and in-category-id exists, unless they have sub-ids that are different from each
 * other. One entry having a sub-id and the other NOT having a sub-id counts as the sub-ids being different.
 * @package App\Rules
 */
class UniqueCategoryId implements Rule
{
    /**
     * @var int
     */
    private $category;
    /**
     * @var int
     */
    private $except;
    /**
     * @var string
     */
    private $subid;

    /**
     * Create a new rule instance.
     *
     * @param int $category the category in which this ID should be unique
     * @param string $subid the sub-id used for this entry
     * @param int $except entries to exempt from the uniqueness check (for updating instead of creating)
     */
    public function __construct(int $category, ?string $subid, int $except = null)
    {
        $this->category = $category;
        $this->except = $except;
        $this->subid = $subid;
    }

    /**
     * Determine if the validation rule passes.
     *
     * @param  string  $attribute
     * @param  mixed  $value
     * @return bool
     */
    public function passes($attribute, $value)
    {
        $entries = Entry::whereInCategoryId($value)
            ->whereInCategorySubId($this->subid)
            ->whereCategoryId($this->category)->get();
        foreach($entries as $entry) {
            if ($entry->id !== $this->except) {
                /*
                 * The entry we're looking at has the same sub-id as the newly submitted/updated entry,
                 * and is not exempted. The validation fails.
                 */
                return false;
            }
        }
        return true;
    }

    /**
     * Get the validation error message.
     *
     * @return string
     */
    public function message()
    {
        return 'The category-id must be unique within this category, unless a different sub-id is set.';
    }
}