Assign template to custom page type?

Question

I have created a custom page type (using post state) for my project, so that I can select the page in the Reading settings like you do for page for posts and also for the home page. This is all working fine, and I have assigned ACF fields to turn up only for this page type.

However, I want to use this page so that any amount of content can be added, but also so that the archive list/loop for the custom post type which this page will represent will display (think of this page as page for posts but for a custom post type) but how do I assign a template to this page in the same way that WordPress picks up the index.php or home.php or front-page.php templates? I first started with archive-people.php but I have a disconnect between the content saved against the page and the content in the archive.

The below is how I have created and assigned the state:

add_filter( 'display_post_states', function ( $post_states, $post ) {

  if ( intval( get_option( 'people' ) ) === $post->ID) {
    $post_states['people'] = __('People', 'people');
  }

  return $post_states;
}, 10, 2 );

add_action( 'admin_init', function () {
  $id = 'people';
  add_settings_field(
    $id,
    'People Page:',
    function( $args ) {
      $id = 'people';
      wp_dropdown_pages( array(
        'name'              => 'People',
        'show_option_none'  => '— Select —',
        'option_none_value' => '0',
        'selected'          => get_option( $id ),
      ) );
    },
    'reading',
    'default',
    array(
      'label_for' => 'field-' . $id,
      'class'     => 'row-' . $id,
    )
  );
} );


add_filter( 'whitelist_options', function ( $options ) {
  $options['reading'][] = 'people';

  return $options;
} );

So I want to end up with a page similar to how wordpress knows that page_for_posts is X page in the admin, or woocommerce does the shop/account pages, for example - whilst I've the settings for this, how do I assign the new state to the php page in my theme? To clarify, I'm not using page attribute driven templates.

Currently this is a solution, which works, but feels unclean - in my page.php:

@php $people_page = (int) get_option('people'); @endphp

@if( $people_page === $post->ID )
  @section('content')
    @while(have_posts()) @php the_post() @endphp
      @include('partials.custom-archive')
    @endwhile
  @endsection
@else //do the regular page

Answer 1

Your question does not seem very clear to me but I believe this is what you are trying to do.

You've created a custom post-type: people. You want to have a template which displays the the archive list as well as the full content of a post which is also assigned to this template. If this sounds right, I think you could continue with what you were trying before, making use of the archive-people.php template.

You'd use archive-people.php to display the archive list of posts for this custom post-type as normal. To get and display content from a specific post/page, either before or after the archive listing, you can use the post ID of the post from which you want to display the content like the below:

// This is the ID of the post from which we want to get the post_content.
$my_post_id = 12; 

// Get the content for our specific post ID.
$my_post_content = apply_filters('the_content', get_post_field('post_content', $my_post_id));

// To print or display the content
echo $my_post_content;