Ok, it’s closer but not finnished.

I have these data:
——————
CPT: rf_shows
name Sendung1
id: 20

CPT: rf_episode
name: Folge1
id: 38

User
name: Hans
id: 2

With this code:

<?php
/*
Title: Sendeplanung
Post Type: rf_episode
*/

piklist('field', array(
  'type'      => 'checkbox',
  'label'     => 'Shows',
  'relate'    => array(
    'scope'     => 'post'
  ),
  'choices'   => piklist(get_posts(array(
    'post_type'   => 'rf_show',
    'numberposts' => -1,
    'orderby'     => 'title',
    'order'       => 'ASC'
  )), array('ID', 'post_title'))
));

piklist('field', array(
  'type'      => 'checkbox',
  'label'     => 'DJs',
  'relate'    => array(
    'scope'     => 'user'
  ),
  'choices'   => piklist(get_users(array(
    'orderby'     => 'display_name',
    'order'       => 'ASC'
  )), array('ID', 'display_name'))
));

I get in wp_postmeta:

post_id: 20
meta_key: __relate_post
meta_value: 38

and in wp_usermeta:

user_id: 2
meta_key: __relate_post
meta_value: 38

Thats OK. But I did not see the user checked in post editor although the database entry is correct (look at the attachment).

Is my use of post-to-user relationship wrong?

Yes, this works, it’s the same like the first field in my first post where I wrote that this works. It works bidirectional in the sense that I get two entries in the postmeta table:

– one that links to the selected post ID of post type ‘rf_show’:
post_id: 528
meta_key: my_relate
meta_value: 38

– and the second that links back (comes from the ‘relate’ parameter):
post_id: 38
meta_key: __relate_post
meta_value: 528

Maybe I’m not precise in my question. My point is that using the same code for a post-to-user relationship I get only one entry in the database. The ‘relate’ parameter does nothing in this case (look my second field in the first post). I get no back-link entry in the database.

Jason said, that I don’t need the back-link, which is true, but it’s confusing that the post-to-post and post-to-user relationship differs on this point. Following this approach (we need only one meta entry) the ‘relate’ parameter is unnecessary.

Then Jason said we should omit the ‘field’ parameter if we use the ‘relate’ parameter, but this
does not work.

So I think I use the following ‘classical’ approach without the ‘relate’ parameter but with a ‘field’ parameter:

piklist('field', array(
    'type' => 'select'
    ,'field' => 'my_relate'
    ,'template'  => 'field'
    ,'label' => 'Relate Posts'
    ,'choices' => piklist(
      get_posts(array(
        'post_type' => 'rf_show'
        ,'numberposts' => -1
        ,'orderby' => 'title'
        ,'order' => 'ASC'
      ))
      ,array('ID', 'post_title')
    )
    ,'attributes'=> array(
      'multiple'  => 'multiple'
    )
  ));

Regards

Thanks Jason for the answer.
It makes things clearer now for me but not clear enough (the ‘we need no field parameter’ part, later). If I understand relationships right in 0.9.9.x they are not bidirectional in the sense that piklist would make two database entries for the relationship. Instead there is only one entry in a meta table (postmeta or usermeta) which links the IDs and the use of the parameters you mention ‘user_has’,’user_belongs’, ‘post_has, ‘post_belongs’ etc.

What confused me was that there were two entries in the postmeta table in my first post-to-post example and I expected the same for the post-to-user relationship. The code for this is from the demo /piklist/add-ons/piklist-demos/parts/meta-boxes/field-relate.php and there IS a field parameter.

A search for ‘relate’ => array in the piklist folder gives three results:
/piklist/add-ons/piklist-demos/parts/meta-boxes/field-relate.php
/piklist/add-ons/piklist-demos/parts/meta-boxes/field-relationship.php
/piklist/parts/fields/post-relate.php

In field-relate.php and post-relate.php are ‘field’ parameters, in field-relationship.php not.

Now following the demo field-relationship.php I see there are 3 fields of ‘type’ => ‘group’ with no ‘field’ parameter.

Based on this here is my test post-to-user code with a field of type ‘group’ that works:

piklist('field', array(
	'type' => 'group',
	'scope' => 'user',
	'label' => __('DJs', 'rf'),
	'relate' => array(
		'scope' => 'post'
	),
	'fields' => array(
		array(
			'type' => 'checkbox',
			'field' => 'ID',
			'choices' => piklist(
				get_users(array(
					'orderby' => 'display_name',
					'order' => 'ASC'
				)),
				array('ID', 'display_name')
			)
		)
	)
));

This way I get entries in the usermeta table (links the selected user IDs to the Post ID).

But how should the code look in a non ‘group’ field type? Transforming to this does not work:

piklist('field', array(
	'type' => 'checkbox',
	'scope' => 'user',
	'label' => __('DJs', 'rf'),
	'relate' => array(
		'scope' => 'post'
	),
	'choices' => piklist(
		get_users(array(
			'orderby' => 'display_name',
			'order' => 'ASC'
		)),
		array('ID', 'display_name')
	)
));

No database entries.

So an example of how to use the ‘relate’ parameter in an ordinary field would be very helpfull.

Thanks for replying, but…

@Jason
Sorry, but no. I need the ‘field’ parameter. Removing the ‘field’ parameter results in no database entries at all, means nothing is stored in the database. I think you get confused with the use of the field type ‘post-relate’ where I not have to give a field parameter because its done in the definition of ‘post-relate’ in /piklist/parts/fields/post-relate.php. But since I use the field type ‘checkbox’ I have to give a ‘field’ parameter. And thats Ok and works in the post to post relationship part.

@jrcreative
No, have tried that all, no success. Notice that we talk not about the ‘scope’ parameter but the use of scope in the ‘relate’ parameter. Look at the definition of ‘post-relate’ in /piklist/parts/fields/post-relate.php:

<div class="wp-tab-panel">
  
  <?php
    piklist('field', array(
      'type' => 'checkbox'
      ,'scope' => 'post_meta'
      ,'field' => '_' . piklist::$prefix . 'relate_post'
      ,'object_id' => $arguments['object_id']
      ,'choices' => piklist(
        get_posts(array(
          'post_type' => $scope
          ,'numberposts' => -1
          ,'orderby' => 'title'
          ,'order' => 'ASC'
        ))
        ,array('ID', 'post_title')
      )
      ,'relate' => array(
        'scope' => 'post'
      )
    ));
  ?>

</div>

The use of ‘scope’ => ‘post’ in the ‘relate’ parameter results in storing the relationship in the postmeta table which is the expected behavior.

Problem is that I get no entry in the usermeta table.

OK, I will be watching that for side effects.
Thanks.

Thank you, it’s working just fine. I can remove meta-boxes from post, page and custom post types using the wordpress IDs for meta-boxes:
https://codex.wordpress.org/Function_Reference/remove_meta_box#Parameters

But some questions remain:
– Can I remove e.g. the post title this way?
– What do you mean with “fields section”?
– Can I use the ‘extend’ feature to remove fields from User Profiles?

Thanks!