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Function Reference/update post meta

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Description

The function, update post meta(), updates the value of an existing meta key (custom field) for the specified post.

This may be used in place of add_post_meta() function. The first thing this function will do is make sure that $meta_key already exists on $post_id. If it does not, add_post_meta($post_id, $meta_key, $meta_value) is called instead and its results are returned.

True will always be returned.

Usage

 <?php update_post_meta($post_id, $meta_key, $meta_value, $prev_value); ?> 

Parameters

$post_id
(integer) (required) The ID of the post which contains the field you will edit.
Default: None
$meta_key
(string) (required) The key of the custom field you will edit.
Default: None
$meta_value
(string) (required) The new value of the custom field.
Default: None
$prev_value
(string) (optional) The old value of the custom field you wish to change. This is to differentiate between several fields with the same key.
Default: None

Examples

Default Usage

<?php update_post_meta(76, 'my_key', 'Steve'); ?>

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: 

<?php update_post_meta(76, 'key_2', 'Hans'); ?>

To change key_1's value from Sad to Happy: 

<?php update_post_meta(76, 'key_1', 'Happy', 'Sad'); ?>

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: 

<?php 
  update_post_meta(76, 'key_1', 'Excited', 'Happy');

  //Or

  update_post_meta(76, 'key_1', 'Excited');

  //To change all fields with the key "key_1":

  $key1_values = get_post_custom_values('key_1', 76);
  foreach ( $key1_values as $value )
    update_post_meta(76, 'key_1', 'Excited', $value);
?>

For a more detailed example, go to the post_meta Functions Examples page.

Related

Custom Fields: the_meta, get_post_meta, add_post_meta, update_post_meta, delete_post_meta, get_post_custom, get_post_custom_values, get_post_custom_keys (See Also: post_meta Function Examples)

See also index of Function Reference and index of Template Tags.
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