Support » Plugins » Hacks » [Runtime Error?] Fatal error: Call to undefined function is_user_logged_in()

  • Hi there,

    I’m writing a plugin in which I relate some posts and data.

    I’m having the following problem:

    – I have a function ie: prefix_get_post_by_meta(), and it contains something like:

    function prefix_get_post_by_meta( $meta_value ){
    	$args = array(
    					'numberposts'	=> 1,
    					'post_type'	=> 'my_post_type',
    					'meta_key'		=> 'my_key',
    					'meta_value'	=> $meta_value
    	// get results
    	$the_query = new WP_Query( $args );
    	// The Loop
    	if ( $the_query->have_posts() ) :
    		while ( $the_query->have_posts() ):
    			return get_the_ID();
    	return false;

    Everything goes great with that function.

    The problem is that at certain point when I use this function in another function for a shortcode or in the front end it doesn’t return anything.

    Imagine I have another function my_shortcode_function()

    function my_shortcode_function(){
           $my_id = prefix_get_id_from_api(); // this gives a unique ID that match with the custom field value
           $the_post_id = prefix_get_post_by_meta( $my_id );
           $output = '';
           if ( $match_id ){
               $output .= '<h1>' . get_the_title( $the_post_id ) . '</h1>';
    	   $output .= '<h1><a href="'. get_permalink( $the_post_id ) .'">' . get_the_title( $the_post_id ). '</a></h1>';
               $output .= 'Nothing for the ID ' . $my_id;
          return $output;
    add_shortcode( 'my_shortcode_function', 'my_shortcode_function' );

    If I invoque the function directly from the shortcode, I get nothing as a response, when the post actually exists.

    If I modify the function to echo the $output, and add that as an action for the init:

    add_action( 'init', 'my_shortcode_function' );

    I get the accurate result on the backend. On the front end, I get the wrong result.


    If I stay with the echo instead of returning the $output, and I call the function directly on my plugin, like


    Then I get this:

    Fatal error: Call to undefined function is_user_logged_in() in /Applications/MAMP/…./wp-includes/query.php on line 2778

    It’s obvious that is a runtime thing. Is there something that I’m missing?

    Every query function end up using WP_Query(), that’s why I assumed that this wasn’t the problem, am I right? (I tried with get_posts just in case and the same happened).

    any help is super appreciated 🙂


Viewing 2 replies - 1 through 2 (of 2 total)
  • Moderator bcworkz


    The fatal error has nothing to do with your problem, it is called too early, before WP is stable. The real issue is why you get a different result on the front end instead of the back end. Different files are loaded for each “end”, so that is probably the explanation. But crucially, what’s missing that you need? I don’t know, and I don’t see anything in the code you posted that would be different for each “end”.

    Have you verified the value assigned to $my_id is the same for each “end”? It’s the only thing I can see that would cause a difference.

    Hey, thanks for taking the time and answering. Yes, $my_id is the same on both “ends”.

    Yes, the fatal error is related to the query and the “moment” when the prefix_get_post_by_meta() function is called.

    I don’t know why, on the back end the function was running the right result, and then in the front end not.

    I actually solved this. I don’t know if it’s the best solution, but it worked for me so far.

    1) Avoided the usage of WP_Query, went with $wpdb instead.
    2) Loaded the prefix_get_post_by_meta() on init.

    Thanks again 🙂

Viewing 2 replies - 1 through 2 (of 2 total)
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