update_post_meta( int $post_id, string $meta_key, mixed $meta_value, mixed $prev_value = '' ): int|bool
Updates a post meta field based on the given post ID.
Contents
Description
Use the $prev_value parameter to differentiate between meta fields with the same key and post ID.
If the meta field for the post does not exist, it will be added and its ID returned.
Can be used in place of add_post_meta() .
Parameters
-
$post_idint Required -
Post ID.
-
$meta_keystring Required -
Metadata key.
-
$meta_valuemixed Required -
Metadata value. Must be serializable if non-scalar.
-
$prev_valuemixed Optional -
Previous value to check before updating.
If specified, only update existing metadata entries with this value. Otherwise, update all entries.Default:
''
Return
int|bool Meta ID if the key didn't exist, true on successful update, false on failure or if the value passed to the function is the same as the one that is already in the database.
More Information
Character Escaping
Post meta values are passed through the stripslashes() function upon being stored, so you will need to be careful when passing in values (such as JSON) that might include \ escaped characters.
Do not store escaped values
Consider the JSON value {"key":"value with \"escaped quotes\""}
<?php
$escaped_json = '{"key":"value with \\"escaped quotes\\""}';
update_post_meta( $id, 'escaped_json', $escaped_json );
$broken = get_post_meta( $id, 'escaped_json', true );
/*
$broken, after passing through stripslashes() ends up unparsable:
{"key":"value with "escaped quotes""}
*/
?>Workaround
By adding one more level of \ escaping using function wp_slash (introduced in WP 3.6), you can compensate for the call to stripslashes()
<?php
$escaped_json = '{"key":"value with \\"escaped quotes\\""}';
update_post_meta( $id, 'double_escaped_json', wp_slash( $escaped_json ) );
$fixed = get_post_meta( $id, 'double_escaped_json', true );
/*
$fixed, after stripslashes(), ends up being stored as desired:
{"key":"value with \"escaped quotes\""}
*/
?>Source
File: wp-includes/post.php.
View all references
function update_post_meta( $post_id, $meta_key, $meta_value, $prev_value = '' ) {
// Make sure meta is updated for the post, not for a revision.
$the_post = wp_is_post_revision( $post_id );
if ( $the_post ) {
$post_id = $the_post;
}
return update_metadata( 'post', $post_id, $meta_key, $meta_value, $prev_value );
}
Changelog
| Version | Description |
|---|---|
| 1.5.0 | Introduced. |
User Contributed Notes
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Note that this function will also return
falsewhen$meta_valueis equal to the value you try to update in database.Update the template used by a page,
Note: if there are multiple values for a single key, all the values will get updated if $prev_value is not set.
¡IMPORTANT If you are working with serialized data, the array is updated with an extra nested array
In order to keep the same structure, update the Object in the 1rst nested position.
Other Examples
Assuming a post has an ID of 76, and the following 4 custom fields:
[key_1] => 'Happy'[key_1] => 'Sad'[key_2] => 'Gregory'[my_key] => 'Steve'To change key_2’s value to Hans:
To change key_1’s value from Sad to Happy:
The fields would now look like this:
[key_1] => 'Happy'[key_1] => 'Happy'[key_2] => 'Hans'[my_key] => 'Steve'Note: This function will update only the first field that matches the criteria.
To change the first key_1’s value from Happy to Excited:
Edit Page template
[/php]
For a more detailed example, go to the post_meta Functions Examples page.
Please note that if your database collation is case insensitive (as with suffix _ci) then
update_post_meta()and delete_post_meta() and get_posts() will update/delete/query the meta records with keys that are upper or lower case. However get_post_meta() will be case sensitive due to WordPress caching. See https://core.trac.wordpress.org/ticket/18210 for more info.Default Usage