Inserting post, thumnail and custom fields with wp_insert_post

Question

I just want to add custom post, a thumbnail of it and custom fields.
Here is my code what I am try is to add post, thumbnail and one custom field. But I not getting the idea how to upload the thumbnail of this specific post. And also how retrieve this post.

$image_url = $_FILES['post_img']['name'];
$tags = $_POST['post_tags'];
$my_post = array(
  //'post_mime_type' => $wp_filetype['type'],
  'post_title'    => wp_strip_all_tags( $_POST['post_title'] ),
  'post_content'  => $_POST['post_content'],
  'post_status'   => 'publish',
  'post_type'     => 'Custamize_post',
  'tags_input'    => array('thread_tag' => $tags),
  'post_author'   => $user_ID
);
$post_link = $_POST['post_link'];


add_post_meta($post_id, 'post_link', $post_link, true); 

I see on some articles they use this code to upload the file.

$upload_dir = wp_upload_dir();
//$image_data = file_get_contents($image_url);
$filename = basename($image_url);
if(wp_mkdir_p($upload_dir['path']))
    $file = $upload_dir['path'] . '/' . $filename;
else
    $file = $upload_dir['basedir'] . '/' . $filename;
file_put_contents($file, $image_url);

$wp_filetype = wp_check_filetype($filename, null );
$attachment = array(
    'post_mime_type' => $wp_filetype['type'],
    'post_title' => 'Custamize_post',
    'post_content' => '',
    'post_status' => 'inherit'
);
$attach_id = wp_insert_attachment( $attachment, $file, $post_id );
require_once(ABSPATH . 'wp-admin/includes/image.php');
$attach_data = wp_generate_attachment_metadata( $attach_id, $file );
wp_update_attachment_metadata( $attach_id, $attach_data );

set_post_thumbnail( $post_id, $attach_id );

But my main concern here is how to connect the post, created above, to this attachment.

Answer 1

You can do this by setting the post_parent with the $attach_id.

$my_post = array(
    'ID' => $attach_id,
    'post_parent' => $my_post_id //retrieved after you inserted your post
);

wp_update_post( $my_post );

Just run this after you have both the ID`s of the Post and the attachment, and you have set the parent of the attachment to be the post.