Rename a Drupal 7 field machine name while maintaining field data

rename-field.php

<?php


/**
 * Rename field_resource_thumbnail to field_reference_thumbnail.
 */
function example_update_7001() {
  _example_update_rename_field('field_resource_thumbnail', 'field_reference_thumbnail');
  _example_update_rename_field('field_resource_short_description', 'field_reference_description');
}

function _example_update_rename_field($old_field_name, $new_field_name) {
  // Rename the data and revision tables and all interior column names.
  foreach (array('data', 'revision') as $table_type) {
    db_query("RENAME TABLE {field_{$table_type}_{$old_field_name}} TO {field_{$table_type}_{$new_field_name}}");
    $columns = db_query("DESCRIBE field_{$table_type}_{$new_field_name}");
    foreach ($columns as $column_info) {
      $old_column_name = $column_info->Field;
      if (strpos($old_column_name, $old_field_name) !== FALSE) {
        $new_column_name = str_replace($old_field_name, $new_field_name, $old_column_name);
        $data_type = $column_info->Type;
        $not_null = $column_info->NULL === 'NO' ? 'NOT NULL' : '';
        db_query("ALTER TABLE {field_{$table_type}_{$new_field_name}} CHANGE $old_column_name $new_column_name $data_type $not_null");
      }
    }
  }

  // Modify the global field configuration data.
  $result = db_query("SELECT * FROM {field_config} WHERE field_name = :old_field_name", array(':old_field_name' => $old_field_name));
  foreach ($result as $row) {
    $data = json_encode(unserialize($row->data));
    $data = str_replace($old_field_name, $new_field_name, $data);
    $data = serialize(json_decode($data, TRUE));
    db_query("UPDATE {field_config} SET field_name = :new_field_name, data = :data WHERE field_name = :old_field_name", array(
      ':new_field_name' => $new_field_name,
      ':data' => $data,
      ':old_field_name' => $old_field_name,
    ));
  }

  // Modify the instance configuration data.
  $result = db_query("SELECT * FROM {field_config_instance} WHERE field_name = :old_field_name", array(':old_field_name' => $old_field_name));
  foreach ($result as $row) {
    $data = json_encode(unserialize($row->data));
    $data = str_replace($old_field_name, $new_field_name, $data);
    $data = serialize(json_decode($data, TRUE));
    db_query("UPDATE {field_config_instance} SET field_name = :new_field_name, data = :data WHERE field_name = :old_field_name AND entity_type = :entity_type AND bundle = :bundle", array(
      ':new_field_name' => $new_field_name,
      ':data' => $data,
      ':old_field_name' => $old_field_name,
      ':entity_type' => $row->entity_type,
      ':bundle' => $row->bundle,
    ));
  }

  // Rename usages in groups.
  $all_group_data = db_query("SELECT * FROM {field_group}");
  foreach ($all_group_data as $row) {
    if (strpos($row->data, $old_field_name) !== FALSE) {
      $data = json_encode(unserialize($row->data));
      $data = str_replace($old_field_name, $new_field_name, $data);
      $data = serialize(json_decode($data, TRUE));
      db_query("UPDATE {field_group} SET data = :data WHERE id = :id", array(
        ':data' => $data,
        ':id' => $row->id,
      ));
    }
  }
}