Hi there,
You can achieve this by looking into this page: http://www.advancedcustomfields.com/resources/querying-relationship-fields/. On the last code example, you can see that you need to query the posts using get_posts(). It will be something like this:
<!-- TESTrel_producers -->
<?php
$TESTrel_producers = new WP_Query( array(
'post_type' => 'producers',
'post__not_in' => array($post->ID),
'posts_per_page' => 20,
'orderby' => 'title', //change it if you want to order by something else
'order' => 'ASC',
'offset' => 0,
) );
?>
<?php if( $TESTrel_producers ): ?>
<div class="content_block_wrap two_columns_right col-md-6">
<div class="content_block transparent_block_with_border">
<div class="block_title">
List of posts of custom post type “producers”, with number of related “movies” posts:
</div>
<ul>
<?php
while ( $TESTrel_producers->have_posts() ) :
$TESTrel_producers->the_post();
?>
<?php
$the_movies = get_posts(array(
'post_type' => array( 'movies' ), // uncomment it if you only want to get the result from movies post type
'posts_per_page' => -1,
'meta_query' => array(
array(
'key' => 'movies_of_this_producer', // name of custom field
'value' => '"' . get_the_ID() . '"', // matches exaclty "123", not just 123. This prevents a match for "1234"
'compare' => 'LIKE'
)
)
));
?>
<li class="content_item col-xs-12">
<a class="post_thumbnail" href="<?php echo get_permalink( $TESTrel_producers->ID ); ?>">
<?php echo get_the_post_thumbnail( $TESTrel_producers->ID, '90x60-thumb' ); ?>
</a>
<a href="<?php echo get_permalink( ); ?>"><?php echo get_the_title( ); ?></a>
<span class="sm">Number of related posts:</span> <?php
echo $producer_count = count($the_movies);
?>
</li>
<?php
endwhile;
?>
</ul>
</div>
</div>
<?php endif; ?>
<?php
wp_reset_postdata();
?>
<!-- TESTrel_producers end -->
I hope that helps.
