fancyfiber

Requires the plug-in <a href="https://wordpress.org/extend/plugins/advanced-custom-fields/" title="Awesome plug-in to manage custom fields" rel="ugc">Advanced Custom Fields</a>.
This is a very basic add-on to allow the ability for relationship fields that are associated with a single related item, to be able to add a new 
item to the related item without leaving the post/page you are currently editing. Uses a colorbox pop-up to open the add new post window with very 
limited options.
Usage:
<ul>
<li>Install the plug-in (standard WordPress installation)</li>
<li>Set up a relationship field with only one related item (standard Advanced Custom Field configuration)</li>
<li>Add or Edit a post with the relationship and the new Add New button will show up on the relationship field</li>
<li>Click the Add New button to open Colorbox add new post for the related item</li>
<li>Click the publish button and the new item will be added (or click the X button to cancel) and the Colorbox will close</li>
<li>The newly added item will be available for selection in the relationship list</li>
</ul>
This plug-in was developed for <a href="http://www.tanabi.com" rel="nofollow ugc">Tanabicom, LLC</a> and <a href="http://www.5dspectrum.com" rel="nofollow ugc">5D Spectrum, Inc</a> by <a href="http://hosting.fancyfiber.com/design/" rel="nofollow ugc">Fancy Fiber Designs</a>

ACF Single Relationship Add New

Add a new related item while editing a post, without leaving the current post.

Jennifer M. Dodd

This plugin creates a user-object relationship table and a user-object relationship metadata 
table. Relationships between a user (logged-in or IP) are created and added to the relationship 
table; metadata (ex. votes, flags, and ratings) is attached to that particular relationship 
via the metadata table. This is a framework; it is intended for use in voting, flagging, 
and similar user applications where a user-affiliated metadata is attached to an object. 
Supported object tables include wp_posts, wp_comments, wp_users, and wp_bp_activity.
Functions are provided to add/get/delete relationships; metadata is added via the native WordPress 
metadata-handling functions. 
Functions provided by this framework include:
<ul>
<li><code>ucc_uof_object_reference()</code> returns an array of object-integer assignments. Use this to look up the 
appropriate value for $object_ref based on the object table (wp_posts, wp_comments, wp_users, 
wp_bp_activity are currently supported) to which you are attaching a user relationship.</li>
<li><code>ucc_uof_add_relationship( $user_id = 0, $user_ip = 0, $object_id, $object_ref )</code> adds a relationship 
to the relationship table if none exists and returns the relationship id for that user/object pairing.</li>
<li><code>ucc_uof_delete_relationship( $user_id = 0, $user_ip = 0, $object_id, $object_ref )</code> will delete a 
relationship if there are no metadata entries left for that relationship.</li>
<li><code>ucc_uof_get_relationship()</code> returns the relationship id for that user/object pairing.</li>
<li><code>ucc_uof_get_user_id()</code> returns the current user id or 0 if not logged in.</li>
<li><code>ucc_uof_get_user_ip()</code> returns 0 if the current user is logged in, or an ip2long() if anonymous.</li>
</ul>
Example code:
<pre><code>// Create or get the user-object relationship.
$relationship = ucc_uof_get_relationship( $user_id, $user_ip, $object_id, $object_ref );
if ( empty( $relationship ) )
 $relationship = ucc_uof_add_relationship( $user_id, $user_ip, $object_id, $object_ref );

// Add user_object_meta.
if ( $mode == 'delete' )
 delete_metadata( 'uof_user_object', $relationship, '_your_meta_key' );
else
 update_metadata( 'uof_user_object', $relationship, '_your_meta_key', 'your meta key value' );
</code></pre>

User Object Framework

Provide a framework for assignment of user-object relationship metadata.

ACF Single Relationship Add New vs User Object Framework