function pa_category_top_parent_id ($catid) {

 while ($catid) {
  $cat = get_category($catid); // get the object for the catid
  $catid = $cat->category_parent; // assign parent ID (if exists) to $catid
  // the while loop will continue whilst there is a $catid
  // when there is no longer a parent $catid will be NULL so we can assign our $catParent
  $catParent = $cat->cat_ID;
 }

return $catParent;
}

//-----------------------------------------------------------
//funcion para mostrar un single template para cada categoria
/**
* Define a constant path to our single template folder
*/
define(SINGLE_PATH, TEMPLATEPATH . '/single');

/**
* Filter the single_template with our custom function
*/
add_filter('single_template', 'my_single_template');

/**
* Single template function which will choose our template
*/
function my_single_template($single) {
	global $wp_query, $post;

/**
	* Checks for single template by category
	* Check by category slug and ID
	*/
	foreach((array)get_the_category() as $cat) :

		$categoriapadre= pa_category_top_parent_id ($cat);

		if(file_exists(SINGLE_PATH . '/single-cat-' . $cat->term_id . '.php'))
			return SINGLE_PATH . '/single-cat-' . $cat->term_id . '.php';

		elseif(file_exists(SINGLE_PATH . '/single-cat-' . $categoriapadre . '.php'))
			return SINGLE_PATH . '/single-cat-' . $categoriapadre . '.php';	

	endforeach;
return $single;

}

Thanks

I’m trying to make this work on twentyten theme. I cant seem to make it work.

Here’s the code:

/* Define a constant path to our single template folder */
define(SINGLE_PATH, TEMPLATEPATH . '/single');

/* Filter the single_template with our custom function*/
add_filter('single_template', 'my_single_template');

/* Single template function which will choose our template*/
function my_single_template($single) {
    global $wp_query, $post;

/* Checks for single template by post type */
if ($post->post_type == "POST TYPE NAME"){
    if(file_exists(SINGLE_PATH . '/single-' . $post->post_type . '.php'))
        return SINGLE_PATH . '/single-' . $post->post_type . '.php';
}

/* Checks for single template by category. Check by category slug and ID */
foreach((array)get_the_category() as $cat) :

    if(file_exists(SINGLE_PATH . '/single-cat-' . $cat->slug . '.php'))
        return SINGLE_PATH . '/single-cat-' . $cat->slug . '.php';

    elseif(file_exists(SINGLE_PATH . '/single-cat-' . $cat->term_id . '.php'))
        return SINGLE_PATH . '/single-cat-' . $cat->term_id . '.php';

endforeach;

/*Checks for default single post files within the single folder */
if(file_exists(SINGLE_PATH . '/single.php'))
    return SINGLE_PATH . '/single.php';

elseif(file_exists(SINGLE_PATH . '/default.php'))
    return SINGLE_PATH . '/default.php';

return $single;
}

and just replace “POST TYPE NAME” with your custom post type name.

How would I modify the code above to maintain the category specific single post templates while also enabling the single post type ones?

What if the element you want to change is not in the single.php file but in the loop.php file? The loop calls the post thumbnail to appear before the post title. But I want, for a specific category, to remove that thumbnail from the loop…

Hopefully I am making myself clear.
Thanks so much for this!

So if we have one post in two or more categories and we want to display the post with comments ability in one category and without comments in the other categories. Is this possible?

Thanks

By the way, I’m running this on WP Multisite 3.0.3 and it works great!