How to check if a post meta key/value pair already exists for a specific post

Question

I want to know if for a given post ID $post_id, there is a metadata key and value pair stored that matches a given key $meta_key and value $meta_value pair.

I am not looking for ANY post that matches the condition, which could easily be achieved with:

get_posts(array(
    'meta_key' => $meta_key,
    'meta_value' => $meta_value
));

But instead, for the given $post_id.

There are probably many different ways to do it:

For example with get_posts():

get_posts(array(
    'post__in' => array($post_id),
    'meta_key' => $meta_key,
    'meta_value' => $meta_value
));

Or looping through all the post meta and checking them all.

$results = get_post_meta($post_id, $meta_key, false);
$found = false;
foreach($results as $result){
   if($result == $meta_value){
   $found = true;
   break;
   }
}

But I want to know if there is any builtin way to do it in WordPress. And if there is not, what the most efficient one would be.

Answer 1

According to the docs of get_post_meta(), you could try

• relying on the return value of the get_post_meta() function, or
• use the get_post_custom_keys() function.

N.B. If you're going for the first option, you could use the object operator -> to get the meta value from the post, and circumvent having to call get_post_meta() yourself. View it on Trac here.