List of Posts in a Custom Field

Question

I have a question. I have a custom post type called Place. I have a situation that there can be place in place. I want to have a custom field parent_place where I could choose a parent of place.
The Place can have none or one parent.

Is there any posibility to list all posts (type = place) in custom field and choose one of them? In plugins for custom fields I can choose dropbox, radio, etc, but I have to type values. How can I automatically fill in a list of all posts which type is Place?

Answer 1

It depends on what plugin you are using to generate your custom fields.

For example the Advanced Custom Fields plugin has this option built in - the field type is called "Post Object".

Documentation:
ACF > Field Types > Post Object

Screenshot:

Answer 2

As Michal Mau points out, ACF is easy and effective to automate this kind of Custom Field/Meta Box management.

The manual mode uses the action hooks add_meta_box and save_post. In this example, you'd have to adjust the indicated arrays to simply array( 'place' ). Check comments for details:

add_action( 'add_meta_boxes', 'add_custom_box_wpse_94701' );
add_action( 'save_post', 'save_postdata_wpse_94701', 10, 2 );

function add_custom_box_wpse_94701() 
{
    // Post types to insert the meta box. Adjust array <-------
    foreach( array( 'post', 'portfolio' ) as $pt )
        add_meta_box(
            'sectionid_wpse_94701',
            __( 'Custom parent' ), 
            'blogroll_box_wpse_94701',
            $pt,
            'side'
        );
}


function blogroll_box_wpse_94701() 
{
    global $post, $typenow;

    // Get all posts of a type, excluding the current post
    $args = array(
        'numberposts' => -1,
        'post_type'   => $typenow,
        'post_status' => 'publish,future',
        'exclude'     => $post->ID,
    );
    $get_posts = get_posts( $args );

    $saved = get_post_meta( $post->ID, 'custom_parent', true);

    // Security
    wp_nonce_field( plugin_basename( __FILE__ ), 'noncename_wpse_94701' );

    // Dropdown
    echo '<select name="custom_parent" id="custom_parent">
        <option value="">- Select -</option>';
    foreach ( $get_posts as $parent_post ) 
    {
        printf(
            '<option value="%d" %s> %s</option>',
            $parent_post->ID,
            selected( $saved, $parent_post->ID, false),
            $parent_post->post_title
        );
    }
    echo '</select>';
}


function save_postdata_wpse_94701( $post_id, $post_object ) 
{
    // Verify auto save 
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) 
        return;

    // Security
    if ( 
        !isset( $_POST['noncename_wpse_94701'] ) 
        || !wp_verify_nonce( $_POST['noncename_wpse_94701'], plugin_basename( __FILE__ ) ) 
        )
        return;

    // Allowed post types. Adjust array <-------
    $allowed_post_types = array( 'post', 'portfolio' );
    if ( !in_array( $post_object->post_type, $allowed_post_types ) )
        return;

    // Process post data
    if ( isset( $_POST['custom_parent'] )  )
        update_post_meta( $post_id, 'custom_parent', $_POST['custom_parent'] );
    else 
        delete_post_meta( $post_id, 'custom_parent' );
}