mysqli - fetch_Array error call to a member function fetch_array() on a non-object mysqli [duplicate]

I am new to mysqli and started trying to learn basic things. With respect to this i example (http://php.net/manual/en/mysqli-result.fetch-array.php) i was trying fetch_array. Here is my code.

$sqlGetChartData    =   "SELECT date, ratepersqft, location 
                          FROM ratepersqft
                         WHERE project_id = 1";
$runGetChartData    =   $mysqli->query($sqlGetChartData);

while($rowGetChartData = $runGetChartData->fetch_array(MYSQLI_BOTH))
    $arrGetChartData[]  =   $rowGetChartData;

    print "<pre>";
    print_r($arrGetChartData);
    exit();

Here i am getting this error Call to a member function fetch_array() on a non-object on line next to while condition line. I tried googling it and did not get result for my problem. Hope my question is clear. Thanks in Advance.

This answer has been written very long time ago and become irrelevant.

Since then I learned the proper solution for this problem and wrote it in this answer. Please navigate there.

The query probably failed and mysqli::query returned FALSE. Therefore $runGetChartData is not a mysqli_result object, but a boolean, which is why you are getting your error.

From the documentation:

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.