Prevent duplicate post from dynamic multiple loops

Question

I was trying to list 20 recent posts, and put a post from custom post type on every 5th item. So it's like:

• Post
• Post
• Post
• Post
• Post
• Custom Post Type
• Post
• Post
• Post
• Post
• Post
• Custom Post Type .. and so on.

Here's what I did so far. It's working but the custom post types is still duplicating, even when the orderby set to random.

<?php $counter = 1;
$loop = new WP_Query( array( 'post_type' => 'post', 'posts_per_page' => 20) );
while ( $loop->have_posts() ) : $loop->the_post(); ?>
<li class="group">
Post Content
</li>
<?php
if ($counter % 5 == 0){
  $inner_query = new WP_Query(array( 'post_type' => 'custom-type', 'posts_per_page' => 1, 'orderby' => 'rand'));
  while ($inner_query->have_posts()) : $inner_query->the_post(); ?>
  <li>Custom Post Type Content</li>
  <?php endwhile;
}
$counter++ ;
endwhile; ?>

How to prevent duplicate posts on the custom post type?

Thanks!

Answer 1

Don't run a new query for your CPT at every iteration of the main Loop. Pull it once, outside the Look with 'posts_per_page' => 4 then increment it as you go.

In other words:

$counter = 1;
$loop = new WP_Query( 
  array( 
    'post_type' => 'post', 
    'posts_per_page' => 20
  ) 
);

$inner_query = new WP_Query(
  array( 
    'post_type' => 'page', 
    'posts_per_page' => 4, 
    'orderby' => 'rand'
  )
);

while ( $loop->have_posts() ) {
  $loop->the_post(); ?>
  <li class="group"><?php
    the_title(); 
    echo '('.$post->post_type.')'; ?>
  </li><?php
  if ($counter == 5) {
    if ($inner_query->have_posts()) {
      $inner_query->the_post(); ?>
      <li><?php
        the_title(); 
        echo '('.$post->post_type.')'; ?>
      </li><?php
    }
    $counter = 0;
  }
  $counter++ ;
}

You have to be very careful with counters and think through the logic or you will get unexpected results.

Secondly, I simplified your logic. There is no need for the mod math if you use a counter as you do. However, there is a way to do away with the counter altogether, as WP_Query provides one for you.

while ( $loop->have_posts() ) { 
  $loop->the_post(); ?>
  <li class="group"><?php
    the_title(); 
    echo '('.$post->post_type.') ('.$loop->current_post.')'; ?>
  </li><?php
  if ($loop->current_post != 0 && ($loop->current_post+1) % 5 == 0) {
    if ($inner_query->have_posts()) {
      $inner_query->the_post(); ?>
      <li><?php
        the_title(); 
        echo '('.$post->post_type.')'; ?>
      </li><?php
    }
  }
}