Post object, Page link, Relationship, Taxonomy and User

Relational fields point to other things in WordPress. They store IDs, not copies, so a renamed post or term shows its new name everywhere.

Common behaviour:

• IDs are checked when saved: an ID that does not exist, or is not allowed by the field's settings, is dropped.
• The stored IDs are not removed when the target is later deleted. wpmcf_get_field() returns what is stored; the printed output skips items that no longer exist.
• Pickers search through a protected admin route, so they need an editor who may edit posts (User fields need the right to list users). Post object, Page link, Relationship and User are not available in front-end forms (Pro). Taxonomy is.

Post object

Chooses one post, page or custom post type entry.

On the edit screen an editor types in the Search posts… box and clicks a result. Search covers published, scheduled, draft, pending and private posts the editor is allowed to read, 20 results at a time, with the post type (and the status, if not published) next to the title.

What is saved. One ID. If several are posted, the last one is used. The post must exist, be of an allowed type and be readable by the current user; an editor cannot link a draft they cannot see. A post that was already linked stays linked even when the editor cannot see it, so editing never unlinks it silently.

What is printed. The post title as a link to the post when visitors can open it. Visitors who cannot open the post (a draft, private or password-gated item) see nothing; users who can read it see the plain title.

$id = wpmcf_get_field( 'review', 'product' );           // 708 (int) or null

if ( $id ) {
    printf( '<a href="%s">%s</a>', esc_url( get_permalink( $id ) ), esc_html( get_the_title( $id ) ) );
}

wpmcf_the_field( 'review', 'product', null, [ 'wrap' => false ] );
// <a href="http://example.com/blue-widget/">Blue widget</a>

[wpmcf_field group="review" field="product" wrap="false"]

Page link

Works like Post object, but prints the post's address (permalink) as the link text, which is useful for plain "go to this page" links. It uses the same Post types setting (default Post; set it to Page to link to pages).

[wpmcf_field group="review" field="landing" wrap="false"]
→ <a href="http://example.com/pricing/">http://example.com/pricing/</a>

Only posts visitors can open are printed; a draft prints nothing (even though its ID is stored). In templates, use the ID with get_permalink():

$id = wpmcf_get_field( 'hero', 'landing' );
if ( $id && 'publish' === get_post_status( $id ) ) {
    echo '<a href="' . esc_url( get_permalink( $id ) ) . '">' . esc_html( get_the_title( $id ) ) . '</a>';
}

You can switch a field between Post object and Page link without losing data.

Relationship

Chooses several posts and keeps them in the order picked. The picker has no drag handle: to change the order, remove an item (×) and pick it again.

What is saved. A list of unique IDs of existing, readable posts of the allowed types, in the order posted. An empty selection clears the field.

What is printed.

<ul class="wpmcf-relationship">
  <li><a href="http://example.com/page-one/">Page one</a></li>
  <li><a href="http://example.com/page-two/">Page two</a></li>
</ul>

Only posts visitors can open are listed; if none are public, nothing is printed.

$ids = wpmcf_get_field( 'course', 'lessons' );          // [708, 709]  (int[]), or [] if empty

if ( $ids ) {
    $lessons = get_posts( [ 'post__in' => $ids, 'orderby' => 'post__in', 'post_type' => 'any', 'posts_per_page' => count( $ids ) ] );
    foreach ( $lessons as $lesson ) {
        echo '<h3>' . esc_html( get_the_title( $lesson ) ) . '</h3>';
    }
}

orderby => post__in keeps the order the editor chose.

CSV imports take comma-separated post IDs (708,709,710).

Taxonomy

Chooses terms of one taxonomy (categories, tags, a custom taxonomy). The IDs are stored in this field; optionally the post's real terms are kept in sync as well.

Notes:

• A list of more than 300 terms is not shown in full; the field switches to the search box instead (in front-end forms it shows "This list is too long to show here.").
• Save terms and Load terms work for top-level taxonomy fields on posts. They work on the edit screen, the REST API and wpmcf_update_field().
• Load terms only changes what the edit screen shows. The value stored in the field (and returned by wpmcf_get_field()) is updated when the post is saved. If terms are changed elsewhere, wpmcf_get_field() can differ from wp_get_object_terms(). When the real terms matter, read them with WordPress functions.

$term_ids = wpmcf_get_field( 'project', 'topics' );     // [12, 13]  or []

$names = wp_list_pluck( get_terms( [ 'include' => $term_ids, 'taxonomy' => 'category', 'hide_empty' => false ] ), 'name' );

What is printed. Term names separated by commas; each name links to its archive when the taxonomy has public archives.

[wpmcf_field group="project" field="topics" wrap="false"]
→ <a href="http://example.com/category/news/">News</a>, <a href="http://example.com/category/news/local/">Local</a>

CSV imports take comma-separated term IDs, slugs or names.

User

Chooses users, optionally only some roles.

• The result is always a list, even with Maximum users 1: [19], not 19. Use $ids[0] ?? null.
• User search matches the login, nicename and display name, never email addresses. Only people who can list users can search.
• IDs of users who do not exist or have a role that is not allowed are dropped on save.

$ids = wpmcf_get_field( 'project', 'owners' );          // [1, 19]
foreach ( (array) $ids as $user_id ) {
    $user = get_userdata( $user_id );
    if ( $user ) {
        echo esc_html( $user->display_name );
    }
}

[wpmcf_field group="project" field="owners" wrap="false"]   → Ada, Fatih

The printed output is the display names, comma separated, without links. CSV imports take comma-separated user IDs or logins.

Troubleshooting

• My picker lists nothing. The field's Post types (or Roles) filter excludes the items, or the editor lacks the permission to read them.
• The related page prints nothing on the site. The post is a draft, private or otherwise not public. IDs are stored, but only public items print.
• wpmcf_get_field() returns the ID of a deleted post. Stored IDs are not cleaned when a target is deleted; test with get_post( $id ).
• I linked a page with Post object and it will not save. The field's Post types is still Post. Add Page.