php mysqli query expects parameter 1 be to string

Question

I was coding a User database which calls an static method of find_all which calls an query method which in turn returns all the value of a database but i am finding trouble in d

Answer 1

Just read docs:
mixed

mysqli_query ( mysqli $link , string $query [, int $resultmode = MYSQLI_STORE_RESULT ] )    

You must change your arguments to

mysqli_query($this->connection, $sql)