title: wordpress save multiple value from select item
body: <p>i've created a meta box with a multiple select item that takes its values from a custom post type.</p>
  
  <pre><code>add_action("add_meta_boxes", "palinsesto_box");
  
  function palinsesto_box() {
  add_meta_box("palinsesto-meta", "Speakers",   "palinsesto_manager_meta_options", "palinsesto",   "side");}
  
  function palinsesto_manager_meta_options($post)
  {
  wp_nonce_field( 'radio_schedule', 'schedule_noncename' );
  echo '&lt;label for="speaker_id"&gt;';
  _e("Speaker", 'speaker_id' );
  echo '&lt;/label&gt; ';
  $args = array( 'post_type' =&gt; 'speaker');
  $loop = new WP_Query( $args );
  echo '&lt;select name="speaker_id[]" id="speaker_id" multiple="multiple"&gt;';
  foreach($loop-&gt;posts as $dj):
      if($dj-&gt;ID == get_post_meta( $post-&gt;ID, 'speaker_id', true ))
      {
          $select = 'selected';
      }else{
      $select = '';
  }
  echo '&lt;option value="'.$dj-&gt;ID.'" '.$select.'&gt;'.$dj-&gt;post_title.'&lt;/option&gt;';
  endforeach;
  echo '&lt;/select&gt;';
  echo '&lt;p&gt;Tieni premuto CTRL per selezionare più speakers&lt;/p&gt;';
  }
  </code></pre>
  
  <p>this part works!Now i would save the selected values and display it in a custom column and here there is something worng.</p>
  
  <pre><code>add_action('save_post', 'save_palinsesto_manager_meta_options');
  function save_palinsesto_manager_meta_options($post_id)
  {global $post;
  if ( defined('DOING_AUTOSAVE') &amp;&amp; DOING_AUTOSAVE ){
      //if you remove this the sky will fall on your head.
      return;
  }else{
      if( isset( $_POST['speaker_id'] ) ) {  
      update_post_meta( $post_id,'speaker_id', esc_attr( $_POST['speaker_id'] ) );  
  }
  }
  }
  
  add_filter('manage_palinsesto_posts_columns', 'columns_palinsesto');
  function columns_palinsesto($old_columns)
  {
  $new_columns = array(
      'cb'     =&gt; '&lt;input type="checkbox"&gt;',
      'img'    =&gt; 'Immagine',
      'title'  =&gt; __('Palinsesto'),
      'conduce' =&gt; 'Conduce',
  
  );
  return array_merge( $new_columns, $old_columns );
  }
  
  add_action('manage_palinsesto_posts_custom_column', 'get_palinsesto_columns',
  10, 2);
  function get_palinsesto_columns($col, $post_id)
  {global $post;
  
  $conduce=get_post_meta( $post_id,'speaker_id',$value );
  
  
  switch($col) {
  case 'img':
      if(has_post_thumbnail($post_id)) {
          echo get_the_post_thumbnail($post_id);
      } else {
          echo 'Nessuna immagine!';
      }
      break;
  case 'conduce':
  
      echo $conduce;
      break;
  }
  }
  </code></pre>
  
  <p>This part of code only returns one value and displays the word array or numbers....can u help me????</p>