Excluding categories from admin

Are these traditional Categories ( built-in Posts ) or a Custom Taxonomy? By default, Posts get set to Uncategorized whenever a category is not set but this is not the case with a Custom Taxonomy.

They are custom posts, so no Uncategorized.

If I had the Uncategorized auto set on new posts, the user would have to un-set it manually, right? Or not?

Here’s a little function you may add which will add a default term if the user hasn’t set terms when publishing the post:

/** Add Default Terms to Taxonomy **/
function set_default_object_terms( $post_id, $post ) {

	// Only run this if the user is publishing their post
	if ( 'publish' === $post->post_status ) {

		// An array of taxonomies and their default terms, you can add as many taxonomies as you like.
		$defaults = array(
			'TAXONOMY_SLUG_HERE' => array( 'DEFAULT_CATEGORY_SLUG_HERE' ),
		);

		// Get all taxonomies of the post type
		$taxonomies = get_object_taxonomies( $post->post_type );

		// Loop through each taxonomy
		foreach ( (array) $taxonomies as $taxonomy ) {

			// Get all the post terms
			$terms = wp_get_post_terms( $post_id, $taxonomy );

			// IF there are no terms and our taxonomy exists for this post type, set a default term(s)
			if ( empty( $terms ) && array_key_exists( $taxonomy, $defaults ) ) {
				wp_set_object_terms( $post_id, $defaults[$taxonomy], $taxonomy );
			}
		}
	}
}
add_action( 'save_post', 'set_default_object_terms', 100, 2 );

So, if the user publishes a post without any terms assigned, it will assign one. This will ensure that every post has a category set. Let me know if you have any questions on it.

Thanks for this, actually in the meantime I’ve just added post_category to my wp_insert_post().

$post = array(
	'post_status'	=> 'pending',
	'post_type'		=> 'my_post_type',
  'post_category' => array( 1 ),
);