I'm creating a plugin to display schema script for my WooCommerce product. I use a custom field to add my gtin number in WooCommerce.

This is what I did:

<?php
    $gtin = get_post_meta(post_ID,'gtin',true);
?>
<script type="application/ld+json">{
    "gtin13:"<?php echo $gtin;?>"</script>}

The result:

"gtin13:"1112223334"

Which work fine…

But sometime products doesn't have gtin number, so I created function like this:

1. go check if there is gtin number or not?
2. If don't echo "identifier_exit:false"
3. If found gtin number echo "gtin13:gtin number"
   

     <?php
         function check_gtin() {
             $gtin=get_post_meta(post_ID,'gtin',true);
             if ($gtin!='') {
                 echo '$gtin13:$gtin';
             } else {
                 echo 'identifier_exits:false';
             }
         }
     ?>
    <script type="application/json+ld">{
        "<?php check_gtin();?>"</script>}

The result:

"gtin13:$gtin"

What I am expecting:

"gtin13:1112223334"

So can someone point to me what I did wrong?

I'm creating a plugin to display schema script for my WooCommerce product. I use a custom field to add my gtin number in WooCommerce.

This is what I did:

<?php
    $gtin = get_post_meta(post_ID,'gtin',true);
?>
<script type="application/ld+json">{
    "gtin13:"<?php echo $gtin;?>"</script>}

The result:

"gtin13:"1112223334"

Which work fine…

But sometime products doesn't have gtin number, so I created function like this:

1. go check if there is gtin number or not?
2. If don't echo "identifier_exit:false"
3. If found gtin number echo "gtin13:gtin number"
   

     <?php
         function check_gtin() {
             $gtin=get_post_meta(post_ID,'gtin',true);
             if ($gtin!='') {
                 echo '$gtin13:$gtin';
             } else {
                 echo 'identifier_exits:false';
             }
         }
     ?>
    <script type="application/json+ld">{
        "<?php check_gtin();?>"</script>}

The result:

"gtin13:$gtin"

What I am expecting:

"gtin13:1112223334"

So can someone point to me what I did wrong?

• php
• functions
• woocommerce-offtopic

2 Answers 2

There are some errors as get_post_meta() first argument need to be a defined product ID here (and in your code post_ID is not even dynamic variable and will not give anything)…

Try the following:

<?php
     function check_gtin(){
         if ( $gtin = get_post_meta(get_the_id(), 'gtin', true) ){
             echo "gtin13:". $gtin;
         } else {
             echo 'identifier_exits:false';
         }
     }
 ?>

Then:

<script type="application/json+ld">{"<?php check_gtin(); ?>"</script>

It should better work…

One problem is that you need to pass the $post_id to the function so it has something to work with.

global $post;

check_gtin( $post->ID );

function check_gtin( $post_id ) { /* ... */ }

Another problem is that in PHP single quotes are meant to be literal strings and will not print the variables in them. There's a couple ways to convert this into working code:

Double Quotes

echo "gtin13:{$gtin}";

String Concatenation

echo 'gtin13:' . $gtin;

Formatted Printing

printf( 'gtin13:%s', $gtin );

Additionally, depending on how you're setting the post meta it could return something "empty" but not necessary an empty string ''. Personally, I prefer to use empty() to check if something exists. This will check for empty arrays, empty strings, 0, false.

To bring it altogether, it could look like:

/**
 * Display GTIN
 *
 * @param Integer $post_id
 *
 * @return void
 */
function check_gtin( $post_id ) {

    $gtin = get_post_meta( $post_id, 'gtin', true );

    if( ! empty( $gtin ) ) {
        echo "gtin13:{$gtin}";
    } else {
        echo 'identifier_exits:false';
    }

}