How do I assign a block template (.html) to a custom post type?

Question

I'm using WordPress 6.0 and I've created a child theme from TwentyTwentyTwo. I've created a custom post type using code like this:

register_post_type('foobar', [
   'public' => true,
   'show_in_rest' => true, // enable block editor
   // etc
]);

In my child theme, I've created the directory templates, and within it, a file named foobar.html. I've copied the contents of single.html from twentytwentytwo/templates/ to this folder and renamed it to foobar.html to make it match the custom post type.

If I open the site editor, and click "Templates", I see these templates listed:

• Single Post
• Page
• foobar
• Home
• Search
• etc...

However, when I create a new post of the custom post type foobar using the WordPress admin interface, the default template is "Default template", and not "foobar". How do I change the default block template for a custom block type?

Answer 1

Classic and block(-based) themes both use the same template hierarchy, so for example in classic themes, we can add a template named single-<post type>.php which would be used as the default template for displaying single posts in a specific post type, and in block themes, the equivalent template is named single-<post type>.html, but that template must be placed in the templates directory (e.g. at wp-content/themes/your-theme/templates) as opposed to the theme's root directory in classic themes.

So you should rename your template to single-foobar.html and WordPress will automatically load it on single post pages in the foobar post type, e.g. at https://example.com/foobar/foo-1/.

However, to make it appear as the "Default template", e.g. in the "Post tab → Template panel" in the block editor's sidebar, you need to register the template as a default template using the default_template_types hook:

add_filter( 'default_template_types', 'my_theme_default_template_types' );
function my_theme_default_template_types( $template_types ) {
    $template_types['single-foobar'] = array(
        'title'       => 'Single Foobar',
        'description' => 'Displays a single foobar post.',
    );

    return $template_types;
}

Preview (WordPress v6.0.1):

So I hope that helps and you should check the Differences and similarities between classic themes and block themes, and you might also want to learn about registering custom templates: _{(which in classic themes, they use a header line, i.e. a PHP comment like Template Name: Foobar)}

• https://developer.wordpress.org/themes/advanced-topics/theme-json/#defining-custom-templates

• https://developer.wordpress.org/block-editor/how-to-guides/themes/theme-json/#customtemplates