How to save value for a field to node or user - Drupal 7 :: entity module
  Introduction   The contributed  Entity API  module provides wrapper classes that make dealing with the values of an entity's properties and fields easier.   If you need to save a text or numeric value into a field you must pass the value as below,   <?php  $node = node_load($nid);//Node ID  $node_wrapper = entity_metadata_wrapper('node', $node);  $var = $node_wrapper->field_age->value() + 1;  $node_wrapper->field_age->set($var);  $node_wrapper->save();   ?>  Note: to update the user value you can use user_load($uid);   If you need to save a file into a field you must pass the file object or an array with a ``fid`` key:   <?php    $node = node_load($nid); //Node ID    $containing_node = entity_metadata_wrapper('node', $node);     // Load the file object in any way    $file_obj = file_load($fid);    $containing_node->field_attachment_content->file->set( $file_obj );    // ..or pass an array with the fid    $co...