Single taxonomy for different custom post types

Question

I have two custom post types: books and authors. Both of them have attached a custom taxonomy - genres.

How would I display the books in the fiction genre?

What would be the URL used and the name of the template?

I can think of two methods to do this, but they have disadvantages, so I'm looking for a method that that would be similar with WP template hierarchy: visiting site.com/genre/fiction/ would call this template taxonomy-genre.php

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Method 1: using custom page templates I would create a custom page template, cpt-genre.php. Then, I would create an empty page for each genre in books, using slugs like books-fiction and so on. In the template, I'd read the slug of the page, interpret it and query to get the books in fiction genre.
Result: accessing site.com/books-fiction would get to cpt-genre.php, and the template would display the data based on the slug of the page.
Downside: difficult to administer

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Method 2: add a query string to the the taxonomy URL, read it in taxonomy-books.php and taxonomy-authors.php and modify WP_Query to display only the books / authors in the mentioned genre.
Result: accessing site.com/books/?genre=fiction would get to taxonomy-books.php, and the template would display the data based on the query string.
Downside: the URL is not clean and, also, it's not SEO friendly

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So, any other ideas for new methods or, at least, for ways to mitigate the downsides of the above methods?

Answer 1

I think this is what you are searching for... You must use both post_type and tax_query to filter your query

 $query = new WP_Query( array(
    'post_type' => 'books',          // name of post type.
    'tax_query' => array(
        array(
            'taxonomy' => 'fiction',   // taxonomy name
        )
    )
) );

while ( $query->have_posts() ) : $query->the_post();
    // do stuff here....
endwhile;

/**
 * reset the orignal query
 * we should use this to reset wp_query
 */
wp_reset_query();

Answer 2

Similarly, do you need to display just the authors per genre?

If not, then you can hook on pre_get_posts and just remove the author post type from the query's post types (or re-set the whole thing to books) when is_tax( 'genre' ) is true.