Different template for posts of all subcategories of category

Question

I want to use different template for posts of all subcategory of one category. Below is the Code I am using :

add_filter( 'single_template', 'get_custom_cat_template' ) ;
function get_custom_cat_template( $single_template ) {
    global $post;
    if ( is_category( 'blog' ) || in_category( 'blog' ) ) {
        $single_template = dirname( __FILE__ ) . '/single-blog.php';
    }

    return $single_template;
}

Here "blog" is the category. This code is working for parent category (blog) only. For posts of subcategory, it is loading default single.php file.

How can I change the code so that it works for all subcategories of parent category?

Answer 1

You can check if current category is a child of blog category with cat_is_ancestor_of() function or term_is_ancestor_of(), or maybe better, use in_category(), as you are currently doing, but checking child categories as well.

add_filter( 'single_template', 'get_custom_cat_template' ) ;
function get_custom_cat_template( $single_template ) {


    // You want to filter only template for single posts of default post type    
    if( is_singular( 'post' ) ) {

        $post = get_queried_object();
        // Replace '3' with the ID of the 'blog' category
        $child_blog_categories = get_term_children( '3', 'category' );

        if ( in_category( 'blog', $post ) || in_category( $child_blog_categories, $post ) ) {

            $single_template = locate_template( 'single-blog.php' );

        }

    }

    return $single_template;
}

Anyway, I think that if you see yourself creating a category of posts to manage posts whithin that category in a different way, you may want to check out custom post types.