update_post_meta()

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update_post_meta( int $post_idstring $meta_keymixed $meta_valuemixed $prev_value =  )

Updates a post meta field based on the given post ID.

Description 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().


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Parameters Parameters

$post_id

(int) (Required) Post ID.

$meta_key

(string) (Required) Metadata key.

$meta_value

(mixed) (Required) Metadata value. Must be serializable if non-scalar.

$prev_value

(mixed) (Optional) Previous value to check before updating. If specified, only update existing metadata entries with this value. Otherwise, update all entries.

Default value: ”


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Return 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.


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More Information More Information

Character Escaping 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 Do not store escaped values

Consider the JSON value {"key":"value with \"escaped quotes\""}

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<?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""}
*/
?>

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Workaround 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()

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<?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\""}
*/
?>

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Source Source

File: wp-includes/post.php

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function update_post_meta( $post_id, $meta_key, $meta_value, $prev_value = '' ) {
    // Make sure meta is added to the post, not 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 );
}


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Changelog Changelog

Changelog
VersionDescription
1.5.0Introduced.
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