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The best way to understand what a hook does is to look at where it occurs in the source code.
do_action( "hook_name" )
apply_filters( "hook_name", "what_to_filter" )
.Remember, this hook may occur in more than one file. Moreover, the hook's context may change from version to version.
This hook occurs 2 times in this file.
Line | Code |
---|---|
439 | * @since 3.1.0 |
440 | * |
441 | * @param null|array|string $value The value get_metadata() should |
442 | * return - a single metadata value, |
443 | * or an array of values. |
444 | * @param int $object_id Object ID. |
445 | * @param string $meta_key Meta key. |
446 | * @param string|array $single Meta value, or an array of values. |
447 | */ |
448 | $check = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, $single ); |
449 | if ( null !== $check ) { |
450 | if ( $single && is_array( $check ) ) |
451 | return $check[0]; |
452 | else |
453 | return $check; |
454 | } |
455 |
|
456 | $meta_cache = wp_cache_get($object_id, $meta_type . '_meta'); |
457 |
|
Line | Code |
488 | */ |
489 | function metadata_exists( $meta_type, $object_id, $meta_key ) { |
490 | if ( ! $meta_type ) |
491 | return false; |
492 |
|
493 | if ( ! $object_id = absint( $object_id ) ) |
494 | return false; |
495 |
|
496 | /** This filter is documented in wp-includes/meta.php */ |
497 | $check = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, true ); |
498 | if ( null !== $check ) |
499 | return (bool) $check; |
500 |
|
501 | $meta_cache = wp_cache_get( $object_id, $meta_type . '_meta' ); |
502 |
|
503 | if ( !$meta_cache ) { |
504 | $meta_cache = update_meta_cache( $meta_type, array( $object_id ) ); |
505 | $meta_cache = $meta_cache[$object_id]; |
506 | } |