From 682ad44a506ea21640b9c052e801a7f75ed4bd9a Mon Sep 17 00:00:00 2001
From: Angie Byron <webchick@24967.no-reply.drupal.org>
Date: Fri, 30 Apr 2010 19:24:03 +0000
Subject: [PATCH] #775936 by nvahalik, jhodgdon, fp: Document
 hook_field_update_forbid().

---
 modules/field/field.api.php | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/modules/field/field.api.php b/modules/field/field.api.php
index 71c97fe5034..1f4eca04808 100644
--- a/modules/field/field.api.php
+++ b/modules/field/field.api.php
@@ -1792,3 +1792,22 @@ function hook_field_storage_purge($entity_type, $entity, $field, $instance) {
  */
 function hook_field_access($op, $field, $entity_type, $entity, $account) {
 }
+
+/**
+ * Allows a module to object to a field definition update.
+ *
+ * The module should throw a FieldUpdateForbiddenException to indicate
+ * that the update should not proceed.
+ *
+ * @param $field
+ *   The updated field structure that a module is attempting to save.
+ * @param $prior_field
+ *   The currently-saved field structure.
+ * @param $has_data
+ *   TRUE if the field has data in storage currently.
+ */
+function hook_field_update_forbid($field, $prior_field, $has_data) {
+  if ($has_data && $field['columns'] != $prior_field['columns']) {
+    throw new FieldUpdateForbiddenException("field_sql_storage cannot change the schema for an existing field with data.");
+  }
+}