Wordpress API: Add / Remove Tags on Posts

I know it seems like a simple operation, but I can't find any resource or documentation that explains how to programmatically add and remove tags to a post using the post ID.

Below is a sample of what I'm using, but it seems to overwrite all the other tags...

function addTerm($id, $tax, $term) {

    $term_id = is_term($term);
    $term_id = intv开发者_如何学Cal($term_id);
    if (!$term_id) {
        $term_id = wp_insert_term($term, $tax);
        $term_id = $term_id['term_id'];
        $term_id = intval($term_id);
    }
    $result =  wp_set_object_terms($id, array($term_id), $tax, FALSE);

    return $result;
}

You need to first call get_object_terms to get all the terms that exist already.

Updated code

function addTerm($id, $tax, $term) {

    $term_id = is_term($term);
    $term_id = intval($term_id);
    if (!$term_id) {
        $term_id = wp_insert_term($term, $tax);
        $term_id = $term_id['term_id'];
        $term_id = intval($term_id);
    }

    // get the list of terms already on this object:
    $terms = wp_get_object_terms($id, $tax)
    $terms[] = $term_id;

    $result =  wp_set_object_terms($id, $terms, $tax, FALSE);

    return $result;
}

Try using wp_add_post_tags($post_id,$tags);

Here is how I do it:

$tag="This is the tag"
$PostId=1; //
wp_set_object_terms( $PostId, array($tag), 'post_tag', true );

Note: wp_set_object_terms() expects the second parameter to be an array.

Since WordPress 3.6 there is wp_remove_object_terms( $object_id, $terms, $taxonomy ) that does exactly that.

The $terms parameter represents the slug(s) or ID(s) of the term(s) to remove and accepts array, int or string.

Source: http://codex.wordpress.org/Function_Reference/wp_remove_object_terms

What if you dont know the post id? You just want to add the tag to all new posts created?

When using the WordPress API function add_action('publish_post', 'your_wp_function');, the function you are calling automatically gets the post_id injected as the first argument:

function your_wp_function($postid) {
}

Actually, wp_set_object_terms can handle everything you need by itself:

If you really need a separate function:

function addTag($post_id, $term, $tax='post_tag') {
    return wp_set_object_terms($post_id, $term, $tax, TRUE);
}

wp_set_object_terms's parameters:

1. the Post ID
2. Accepts...
   • a single string (e.g. 'Awesome Posts')
   • a single ID of an existing tag (e.g. 1), or
   • an array of either (e.g. array('Awesome Posts',1)).
   • NOTE: If you provide a NON-ID, it will create the tag automatically.
3. The taxonomy (e.g. for default tags, use 'post_tag').
4. Whether to...
   • (FALSE) REPLACE ALL existing terms with the ones provided, or
   • (TRUE_) APPEND/ADD to the existing terms.

Happy coding!