update_post_meta()

update_post_meta() — Updates a post meta field based on the given post ID. 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(). For historical reasons both the meta key and the meta value are expected to be “slashed” (slashes escaped) on input.

Inputs: $post_id (int): Post ID. $meta_key (string): Metadata key. $meta_value (mixed): 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 empty.

Returns 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.