Using $wpdb object in Wordpress functions.php file

Question

I have an issue with not being able to call the get_results() function on the $wpdb object inside the Wordpress functions.php file.

Exact error: Call to a member function get_results() on a non-object in [...]

This is my function;

global $wpdb;
function query_students($year){
   $wpdb->get_results(
      $wpdb->prepare(
         "SELECT * FROM {$wpdb->prefix}usermeta WHERE meta_key ='foobar' AND meta_value = '{$year}'"
      )
   );
$wpdb->flush();
}

As you can see I've globalised the $wpdb variable, and this function works great in the page template file. I would just prefer it if my functions weren't dotted around the place, and in some kind of centralised file.

Thanks in anticipation! :)

maiorano84 · Accepted Answer · 2012-09-14 18:28:02Z

3

"Globalizing" a variable that's already in global scope does nothing. Case and point:

global $a; //does nothing
$a = 'foo';
global $a; //does nothing
foo();
echo $a; //'foo'
bar();
echo $a; //'bar'
function foo()
{
    $a = 'bar';
}
function bar()
{
    global $a;
    $a = 'bar';
}

The global keyword does not permanently make the defined variable global in scope. Think of it as a way to define a variable in a function and set its value to whatever a variable with the same name is outside of the function.

You need to move your global declaration INTO the function to make the $wpdb object in the Global scope available within the function's scope:

function query_students($year){
    global $wpdb;
    $wpdb->get_results(
    $wpdb->prepare(
     "SELECT * FROM {$wpdb->prefix}usermeta WHERE meta_key ='foobar' AND meta_value = '{$year}'"
    ));
    $wpdb->flush();
}

edited Sep 14, 2012 at 18:28

answered Sep 14, 2012 at 17:55

maiorano84

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1 Comment

maiorano84 Over a year ago

Anytime. I've added a more in-depth explanation for you in regards to Global variables. They're used pretty heavily in Wordpress, but I would advise against using them unless ABSOLUTELY necessary in standard practice. If this solved your issue, please mark this as answered.

Florent Roques · Accepted Answer · 2023-12-02 10:09:45Z

0

I was running following query in functions.php

SELECT
    `id`,
    `user`,
    `width`,
    `type`,
    `source`,
    `link`,
    `expire`,
    `impressions`,
    `clicks`
FROM adds
WHERE `width` = 728 and `impressions` < (
    SELECT MAX(`impressions`)
    FROM adds
    WHERE `width` = 728
) OR `width`=728 and `clicks` < (
    SELECT MAX(`clicks`)
    FROM adds WHERE `width`=728
) ORDER BY RAND() LIMIT 3

it was not working but after adding the line global $wpdb in the begining of the function helped me and query is running fine. Thanks

edited Dec 2, 2023 at 10:09

Florent Roques

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answered Sep 16, 2013 at 12:44

Focus iTech Solutions

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