查询返回结果但是给出了关于bolean的警告

Question

I am trying to upgrade an old application to PHP 7.2. It contains an sql class PHP file with the following function which I have modified to use mysqli:

    function query($query, $index=0)
    {
        // query
        if (!$this->res[$index] = mysqli_query($this->connection, $query))
        {
            // if query fails show error
            $this->error('<strong>invalid query</strong>:<br />' . $query . '<br />');
            return false;
        }

        // statistical information
        $this->num_rows[$index] = @mysqli_num_rows($this->res[$index]);
        $this->num_flds[$index] = @mysqli_num_fields($this->res[$index]);
        $this->num_aff[$index]  = @mysqli_affected_rows($this->connection);
        $this->last_id             = @mysqli_insert_id($this->connection);

        return true;
    }

This function throws the folling error:

E_WARNING Error in file �sql.class.php� at line 132: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given E_WARNING Error in file �sql.class.php� at line 133: mysqli_num_fields() expects parameter 1 to be mysqli_result, boolean given

My initial thought was that the query was failing. However, including this line inside the function...

print_r(mysqli_fetch_assoc($this->res[$index]));

results in the following output:

Array ( [s_id] => 2088b4cc0d026c2742e8e0cb7d7c8e95 )

In the output above, the query is returning a session ID. That leaves me a bit confused because the value of $this->res[$index] is not a bolean, yet the Warning says it is.

Edit:

If I include this in the function:

        echo mysqli_num_rows($this->res[$index]);
        echo mysqli_num_fields($this->res[$index]);

Each line echos the correct value of 1 but each line also produces the boolean Warning...

E_WARNING Error in file �sql.class.php� at line 125: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given
E_WARNING Error in file �sql.class.php� at line 126: mysqli_num_fields() expects parameter 1 to be mysqli_result, boolean given

Answer 1

mysqli_query return values : If can be mysqli_result object,true, false

Returns FALSE on failure. For successful SELECT, SHOW, DESCRIBE or EXPLAIN queries mysqli_query() will return a mysqli_result object. For other successful queries mysqli_query() will return TRUE.

try this modification to see which query really successful but result was true

function query($query, $index=0)
{
    $this->res[$index] = mysqli_query($this->connection, $query);
    // query
    if (is_bool($this->res[$index])) {
        if ($this->res[$index] === false)
        {
            // if query fails show error
            $this->error('<strong>invalid query</strong>:<br />' . $query . '<br />');
            return false;
        } else {
            // query was successful, but the result is not a mysqli_result object
            $this->warning('<strong>success with no returned data query</strong>:<br />' . $query . '<br />');
            return true;
        }
    }


    // statistical information
    $this->num_rows[$index] = @mysqli_num_rows($this->res[$index]);
    $this->num_flds[$index] = @mysqli_num_fields($this->res[$index]);
    $this->num_aff[$index]  = @mysqli_affected_rows($this->connection);
    $this->last_id             = @mysqli_insert_id($this->connection);

    return true;
}

Check that $this->warning is exist in your code, or update it to what it will be proper