WordPress custom post types: how to show in tag archives (tag.php)

Question

I allow tags on my custom post types like this:

'taxonomies' => array('post_tag'),

My tag.php looks like this:

<h1><?php single_cat_title(''); ?></h1>

<?php while( have_posts() ): the_post(); ?>

<h3><?php the_title(); ?></h3>

<?php endwhile; ?>

However, this is only showing posts with tags from the default post type and not my custom posts types.

I have tried adding the function found here: https://wordpress.stackexchange.com/questions/203239/tag-php-not-displaying-posts-with-the-tag/203241

But the only effect this has is now no posts are showing on the archive.

Answer 1

You must create a custom taxonomy for your custom post type inside the same function you used to create your custom post type.

"product_cat" it's the ID of your custom taxonomy (ie use it in WP_Query) and "array('products') it's the post type ID.

register_taxonomy('product_cat', array('products'), array(
            'hierarchical' => false, // Notice that this one is set to "false".
            'label' => 'Categorias de Produtos', // Sets the name in WordPress backoffice
            'singular_label' => 'Categoria do Produto',
            'rewrite' => array('slug' => 'categoria-producto', 'with_front' => false), // Defines it's URL.
        )
    );

    register_taxonomy_for_object_type('product_cat', 'products');

This will create a tag-like taxonomy for your custom post type

You also need to change this line

"taxonomies" => array("product_cat"),

To the ID of your custom taxonomy or else it won't show up.

Edit: Out of curiosity, setting the "hierarchical" value for "true" will create a category-like taxonomy.

Answer 2

I solved this by editing the function linked in my question to this:

function tag_filter($query) {
  if ( !is_admin() ) {
    if ($query->is_tag) {
      $query->set('post_type', array( 'custom_post_type', ));
    }
  }
}
add_action('pre_get_posts','tag_filter');

What I had to do was remove the check for main query and now all custom posts show on tag archive page using tag.php.