0

I am trying to access a single value from my database through my functions.php. I have tried three different ways to get a result using a dynamic ID and none have worked. I always get NULL as the response. Using a WP_query is not possibility here, so I need to solve this using SQL.

Attempt #1:

global $post;
global $wpdb;
$post_ID = $post->ID;

$result = $wpdb->get_var($wpdb->prepare( 
"
    SELECT meta_value 
    FROM $wpdb->postmeta 
    WHERE post_id = %d
    AND meta_key = 'wpcf-release-date' 
", 
$post_ID
) );

Attempt #2:

$result = $wpdb->get_var("SELECT meta_value FROM $wpdb->postmeta WHERE meta_key = 'wpcf-release-date' AND post_id = $post_ID");

Attempt #3:

$result = $wpdb->get_var("SELECT meta_value FROM $wpdb->postmeta WHERE meta_key = 'wpcf-release-date' AND post_id = " . $post_ID);

I know my query works, I tested the SQL query in Phpmyadmin with a static ID. I can also set the ID manually in my function which will yield a result, but does not help me if it is not dynamic.

SQL Query

SELECT  `meta_value` 
FROM  `wp_postmeta` 
WHERE post_id = 249
AND meta_key =  'wpcf-release-date'

I assume I am overlooking something simple.

  • Expecting Attempt #4: get_post_meta( $post_ID, 'wpcf-release-date', 1 ) – Samuel Elh Jul 11 '16 at 7:57
  • Ha, tried that first which is what caused me to query the DB. – Phawkes Jul 11 '16 at 8:01
  • Lol, the point is, it is really bad to query the DB while there's API to use. FYI, get_post_meta is cached and optimized, unserialized, and loads faster, unlike a direct SQL query, where you add more microseconds to your page load time, and extra server ressource usage.. – Samuel Elh Jul 11 '16 at 8:05
  • Thanks. As I mentioned, I tried that first and it did not work, so I looked for other solutions. – Phawkes Jul 11 '16 at 8:08
  • Sorry. Did you dump $post_ID if it has value? and look right at the PMA if it really has a meta in there? also turn on debugging mode, it might help. – Samuel Elh Jul 11 '16 at 8:11
2

I tested your all attempts in a shortcode:

function add_test_shortcode() {
  global $wpdb;
  global $post;
  $post_ID = $post->ID;
  $wpdb->show_errors = true;
  $result = $wpdb->get_var('SELECT meta_value FROM '.$wpdb->postmeta.' WHERE meta_key="my_test" AND post_id=' . $post_ID);

  return $result;
}
add_shortcode( 'test', 'add_test_shortcode' );

It worked perfectly for me, so there might something from your own code:

1. Check for $post_ID

Make sure your $post_ID is valid, get_the_ID() might be a better replacement in so many cases than global $post;.

2. Test your generated query

You can get your last executed query using $wpdb->last_query, execute it in phpMyAdmin or any other software and check that there is really a result.

3. Look if there's any error

You can get the latest error statement using $wpdb->last_error.

My advice to you during WordPress development is that always keep WP_DEBUG on.

0

Turns out all of my attempts were viable (Thanks ehsaan for also confirming). The issue was that I was trying to get data from a field that was empty at the time of the function. (I was creating a new/updated post that hadn't updated the field yet).

Solution (delay the hook):

// Time out the custom field to update AFTER the post has been created/updated
function save_custom() {
    global $post;
    $post_ID = $post->ID;
    $result = get_post_meta( $post_ID, 'wpcf-release-date', 1 );

    // Add a new key "era"
    add_post_meta($post_ID, "era", $result, true);
    // If there is already a key "era", then update it
    if ( ! add_post_meta($post_ID, "era", $result, true) ) { 
       update_post_meta( $post_ID, "era", $result );
    }
}
add_action('save_post', 'save_custom', 0);
add_action('save_post', 'save_custom', 10);
add_action('save_post', 'save_custom', 999);

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.