Add category in post type dynamically

Question

i have the code that can add a post in a custom post type but adding the category is not working.

$args = array(
    'post_title' => $title ,
    'post_status'   => 'publish',
    'post_type' => 'mypost' 
);

$post_id = wp_insert_post($args);

$category_ids = array(38,39);
wp_set_post_categories( $post_id, $category_ids, 'category');

Answer 1

You need to register the custom post type with support for the category taxonomy:

add_action('init', 'cyb_register_post_type');
function cyb_register_post_type() {
    $args = array(
        // All the other args
        'taxonomies'          => array( 'category' ),
    );

    register_post_type( 'my_post_type', $args );
}

Then you can set relationships between the custom post type and the categoy taxonomy as you was doing, but you have to correct the code.

From this:

wp_set_post_categories( $post_id, $category_ids, 'category');

To this (previous categories are deleted and replaced by the new categories):

wp_set_post_categories( $post_id, $category_ids );
// The above line is equivalent to
// wp_set_post_categories( $post_id, $category_ids, false );
// or
// wp_set_post_terms( $post_id, $category_ids, 'category', false );

Or to (previous categories are not deleted, new categories are appended):

wp_set_post_categories( $post_id, $category_ids, true );

You can also register a custom taxonomy and use it for your custom post type:

add_action('init', 'cyb_register_post_type_and_taxonomy');
function cyb_register_post_type_and_taxonomy() {

    $post_type_args = array(
        // All the other args
        'taxonomies'          => array( 'my_custom_taxonomy' ),
    );

    register_post_type( 'my_post_type', $post_type_args );

    $taxonomy_args = array(
          // Arguments for the custom taxonomy
          // See https://developer.wordpress.org/reference/functions/register_taxonomy/
    );

    register_taxonomy( 'my_custom_taxonomy', 'my_post_type', $args );

}

And then use wp_set_post_terms(), not wp_set_post_categories():

wp_set_post_terms( $post_id, $category_ids, 'my_custom_taxonomy');

Answer 2

As you are doing this for the custom post type, you need to use taxonomy. I will suggest you <?php wp_set_post_terms( $post_id, $terms, $taxonomy, $append ) ?> to use. please refer this link for the detailed use of the function.