Styjun

In my local/development environment, the MySQLi query is performing OK. However, when I upload it on my web host environment, I get this error:

Fatal error: Call to a member function bind_param() on a non-object in...

Here is the code:

global $mysqli;
$stmt = $mysqli->prepare("SELECT id, description FROM tbl_page_answer_category WHERE cur_own_id = ?");
$stmt->bind_param('i', $cur_id);
$stmt->execute();
$stmt->bind_result($uid, $desc);

To check my query, I tried to execute the query via control panel phpMyAdmin and the result is OK.

Sometimes your query fails and you don't know why. Hence it is very important to configure PHP and mysqli to report you every error.

How to get the error message in mysqli

First of all, always have this line before MySQLi connect in all your environments:

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

After that all MySQL errors will be transferred into PHP exceptions. Uncaught exception, in turn, makes a PHP fatal error. Thus, in case of a MySQL error, you'll get a conventional PHP error. That will instantly make you aware of the error cause. A stack trace will lead you to the exact spot where error occurred.

How to configure PHP in different environments

Here is a gist of my article on PHP error reporting:

Note that you have to be able to see PHP errors in general. And here indeed goes the matter of different environments:

You must set the corresponding configuration options to the following values

• 
  

  On a development server

  
  
  
  • 
    error_reporting should be set to E_ALL value;
  
  
  • 
    display_errors should be set to 1
  
  


• 
  

  On a production server

  
  
  
  • 
    error_reporting should be set to E_ALL value;
  
  
  • 
    display_errors should be set to 0
  
  
  • 
    log_errors should be set to 1
  
  

How to actually use it?

Just remove any code that checks for the error manually, all those or die(), if ($result) and such. Just write your database interaction code right away

$stmt = $this->con->prepare("INSERT INTO table(name, quantity) VALUES (?,?)");
$stmt->bind_param("si", $name, $quantity);
$stmt->execute();

again, witohut any conditions around. If an error occurs, then it will be treated as any other error in your code. For example, on a development PC it sill just appear on screen. And for a live site you will need an error wrapper but that's a different story, completely irrelevant to mysqli and its errors.

What to do with the error message you get

After getting the error message, you have to read and comprehend it. It sounds too obvious, but learners often overlook the extreme helpfulness of the error message. Yet most of time it explains the problem pretty straightforward. Say, if it says that particular table doesn't exist, you have to check spelling, typos, letter case, credentials and such. Or, if it says there is an error in SQL syntax, then you have to examine your SQL. And the problem spot is right before the query part cited in the error messaage.

You have to also trust the error message. If it says that number of tokens doesn't match number of bound variables then it is so. The same goes for the absent tables or columns. Given the choice, whether it's your own mistake or the error message is wrong, always stick to the former. Again it sounds condescending, but hundreds of questions on this very site prove this advise extremely useful.

A list of what you should never do in regard of error eporting

• Use error suppression operator (@)


• Use die() or echo or any other function to print the error message on screen unconditionally. PHP can echo it all right already, no assistance is required.


• Testing the query result manually (like if($result)) just makes no sense. Either your query failed and you will already get the error exception, or it was all right and there is nothing to test.


• Use try..catch for echoing the error message. Again PHP can do it better, way better.