How to define a term for custom taxonomy

Question

I have a custom post type called q-questions, and it has a custom taxonomy that called q-categories.
I insert post via wp_insert_post and I want to define some terms for the taxonomy
My code is:

$my_post = array(
'post_title' => 'Custom-tax',
'post_content' => 'This is my post.',
'post_type' => 'q-questions',
 );

$post_id = wp_insert_post( $my_post );

What should I do to define the q-categories for this post as my-category?

Answer 1

A category is just a taxonomy. And taxonomies are made up of terms. You'll need to set the post's terms via wp_set_post_terms.

This should be fairly simple:

wp_set_post_terms( '42', array( 'term', 'terms', 'terms' ), 'q-categories' );

Answer 2

From the Codex:

$post = array(
   ...
  'tax_input' => [ array( 'taxonomy_name' => array( 'term', 'term2', 'term3' ) ) ]  
   ...
);  

So for your example:

$my_post = array(
  'post_title' => 'Custom-tax',
  'post_content' => 'This is my post.',
  'post_type' => 'q-questions',
  'tax_input'=>array(
     'q-categories' => array('my-category'),
   )
 );

$post_id = wp_insert_post( $my_post );

Answer 3

You have to register custom texonomy. Add below code in your functions.php. Ref

//hook into the init action and call create_question_taxonomies when it fires
add_action( 'init', 'create_question_taxonomies', 0 );

//create two taxonomies, genres and writers for the post type "question"
function create_question_taxonomies() 
{
  // Add new taxonomy, make it hierarchical (like categories)
  $labels = array(
    'name' => _x( 'q-categories', 'taxonomy general name' ),
    'singular_name' => _x( 'q-category', 'taxonomy singular name' ),
    'search_items' =>  __( 'Search q-categories' ),
    'all_items' => __( 'All q-categories' ),
    'parent_item' => __( 'Parent q-categories' ),
    'parent_item_colon' => __( 'Parent q-categories:' ),
    'edit_item' => __( 'Edit q-categories' ), 
    'update_item' => __( 'Update q-categories' ),
    'add_new_item' => __( 'Add New q-categories' ),
    'new_item_name' => __( 'New q-categories Name' ),
    'menu_name' => __( 'q-categories' ),
  );     

  register_taxonomy('q-categories',array('question'), array(
    'hierarchical' => true,
    'labels' => $labels,
    'show_ui' => true,
    'show_admin_column' => true,
    'query_var' => true,
    'rewrite' => array( 'slug' => 'q-categories' ),
  ));

}

Then you just add below code after wp_insert_post

wp_set_post_terms( $post_id, array( 'term', 'terms', 'terms' ), 'q-categories' );