Multi select meta box
<p>I have added multi select meta box to custom post-type it appears good but save only one selection . How to change the code below to save all selected options.</p>

<pre><code>add_action( 'add_meta_boxes', 'add_condition_metaboxes'); function add_scondition_metaboxes() {
add_meta_box('condition', 'Информация спикеров', 'wpt_condition_author', 'condition', 'side', 'default');} function wpt_scondition_author() {
global $post;

// Noncename needed to verify where the data originated
echo '&lt;input type="hidden" name="conditionmeta_noncename" id="conditionmeta_noncename" value="' . 
wp_create_nonce( plugin_basename(__FILE__) ) . '" /&gt;';

// Get the author data if its already been entered

$my_dropdown = get_post_meta($post-&gt;ID, '_dappcf_i_dropdown', true);
// Echo out the field

    $posts = get_posts(array('post_type'=&gt; 'speakers', 'post_status'=&gt; 'publish', 'suppress_filters' =&gt; false, 'posts_per_page'=&gt;-1));

        //here you add the HTML of the dropdown you add something like

        echo '&lt;p&gt;Select the speaker: &lt;select multiple="yes" name="_dappcf_i_dropdown" class="widefat"  style="width:170px"&gt;';
        foreach ($posts as $post) {
        echo '&lt;option value="', $post-&gt;ID, '"&gt;'.$post-&gt;post_title.'&lt;/option&gt;';          }
    echo '&lt;/select&gt;'; } function wpt_save_condition_meta($post_id, $post) {

// verify this came from the our screen and with proper authorization,
// because save_post can be triggered at other times
if ( !wp_verify_nonce( $_POST['conditionmeta_noncename'], plugin_basename(__FILE__) )) {
return $post-&gt;ID;
}

// Is the user allowed to edit the post or page?
if ( !current_user_can( 'edit_post', $post-&gt;ID ))
    return $post-&gt;ID;

// OK, we're authenticated: we need to find and save the data
// We'll put it into an array to make it easier to loop though.


$condition_meta['_dappcf_i_dropdown'] = $_POST['_dappcf_i_dropdown'];
// Add values of $testimonial_meta as custom fields

foreach ($condition_meta as $key =&gt; $value) { // Cycle through the $testimonial_meta array!
    if( $post-&gt;post_type == 'revision' ) return; // Don't store custom data twice
    $value = implode(',', (array)$value); // If $value is an array, make it a CSV (unlikely)
    if(get_post_meta($post-&gt;ID, $key, FALSE)) { // If the custom field already has a value
        update_post_meta($post-&gt;ID, $key, $value);
    } else { // If the custom field doesn't have a value
        add_post_meta($post-&gt;ID, $key, $value);
    }
    if(!$value) delete_post_meta($post-&gt;ID, $key); // Delete if blank
} } add_action('save_post', 'wpt_save_condition_meta', 1, 2); // save the custom fields
</code></pre>

<p>The options are queried from other custom post-type and the number of post can be changed. </p>