Add tag to post api wordpress

Question

I have been googling around but could not find the "add tag to post" api/codex. Does anyone know what it is ? Also, the "delete tag from post".

Thanks.

Answer 1

You'll find an index of a good chunk of the WordPress API here on codex. The function you want is wp_set_post_tags(), but follow the links from that page to related functions.

Edit: this should remove a tag from a post, per comment below

// $post is your post object, e.g. from: global $post;
// $target is tag you want to remove

// get an array of current tags on post
$tags = wp_get_post_tags($post->ID, array('fields' => 'names'));

// remove selected tag from array
$key = array_search($target, $tags);
if ($key !== false) {
    unset($tags[$key]);
}

// set new list of tags, without $target
wp_set_post_tags($post->ID, $tags, false);

Answer 2

You would use the wp_insert_term() function to insert a new tag:

wp_insert_term( 'post_tag', 'happy' );

Then after creating your terms, you would add them to the post of your choice using the wp_set_post_terms() function, like so:

wp_set_post_terms( $post_id, 'happy', 'post_tag', true);

Answer 3

Google Knows it.

If you wanted to add a categories to a post with the ID of 42:

$cat_ids = array( 6,8 );
    //to make sure the terms IDs is integers:
    //$cat_ids = array_map('intval', $cat_ids);
    //$cat_ids = array_unique( $cat_ids );
wp_set_object_terms( '42', $cat_ids, 'category' );

If you wanted to clear/remove all categories from a post with the ID of 42:

wp_set_object_terms( '42', NULL, 'category' );

read more about wp_set_object_terms