Laravel по-русски

    public function validate()
    {
        $this->tableExistsValidator();

        parent::validate();
    }

    public function tableExistsValidator()
    {
        Validator::extend('table_exists', function ($attribute, $value, $parameters, $validator) {
            return Schema::hasTable(array_get($this->all(), 'form.tablename', 'test'));
        });
    }

    public function rules()
    {
        return [
            'form.tablename' => 'required|string|table_exists',
        ];
    }