Index: modules/taxonomy/taxonomy.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/taxonomy/taxonomy.module,v
retrieving revision 1.312
diff -u -r1.312 taxonomy.module
--- modules/taxonomy/taxonomy.module	31 Aug 2006 21:58:36 -0000	1.312
+++ modules/taxonomy/taxonomy.module	5 Sep 2006 13:53:03 -0000
@@ -607,18 +607,7 @@
 function taxonomy_form_alter($form_id, &$form) {
   if (isset($form['type']) && $form['type']['#value'] .'_node_form' == $form_id) {
     $node = $form['#node'];
-
-    if (!isset($node->taxonomy)) {
-      if ($node->nid) {
-        $terms = taxonomy_node_get_terms($node->nid);
-      }
-      else {
-        $terms = array();
-      }
-    }
-    else {
-      $terms = $node->taxonomy;
-    }
+    $terms = isset($node->taxonomy) ? $node->taxonomy : array();
 
     $c = db_query(db_rewrite_sql("SELECT v.* FROM {vocabulary} v INNER JOIN {vocabulary_node_types} n ON v.vid = n.vid WHERE n.type = '%s' ORDER BY v.weight, v.name", 'v', 'vid'), $node->type);
 
@@ -724,8 +713,11 @@
 /**
  * Save term associations for a given node.
  */
-function taxonomy_node_save($nid, $terms) {
-  taxonomy_node_delete($nid);
+function taxonomy_node_save($nid, $terms, $old_terms = FALSE) {
+  if ($old_terms === FALSE) {
+    $node = node_load($nid);
+    $old_terms = $node->taxonomy;
+  }
 
   // Free tagging vocabularies do not send their tids in the form,
   // so we'll detect them here and process them independently.
@@ -767,7 +759,7 @@
 
         // Defend against duplicate, different cased tags
         if (!isset($inserted[$typed_term_tid])) {
-          db_query('INSERT INTO {term_node} (nid, tid) VALUES (%d, %d)', $nid, $typed_term_tid);
+          _taxonomy_node_insert_tid($nid, $typed_term_tid, $old_terms);
           $inserted[$typed_term_tid] = TRUE;
         }
       }
@@ -779,18 +771,37 @@
       if (is_array($term)) {
         foreach ($term as $tid) {
           if ($tid) {
-            db_query('INSERT INTO {term_node} (nid, tid) VALUES (%d, %d)', $nid, $tid);
+            _taxonomy_node_insert_tid($nid, $tid, $old_terms);
           }
         }
       }
       else if (is_object($term)) {
-        db_query('INSERT INTO {term_node} (nid, tid) VALUES (%d, %d)', $nid, $term->tid);
+        _taxonomy_node_insert_tid($nid, $term->tid, $old_terms);
       }
       else if ($term) {
-        db_query('INSERT INTO {term_node} (nid, tid) VALUES (%d, %d)', $nid, $term);
+        _taxonomy_node_insert_tid($nid, $term, $old_terms);
       }
     }
   }
+  //delete removed terms
+  if (!empty($old_terms)) {
+    $placeholder = array_fill(0, count($old_terms), '%d');
+    $args = array($nid);
+    $args = array_merge($args, array_keys($old_terms));
+    db_query('DELETE FROM {term_node} WHERE nid = %d AND tid IN ('. implode(',', $placeholder) .')', $args);    
+  }
+}
+
+/*
+ * Helper function for taxonomy_node_save()
+ */
+function _taxonomy_node_insert_tid($nid, $tid, &$old_terms) {
+  if (!array_key_exists($tid, $old_terms)) {
+    db_query('INSERT INTO {term_node} (nid, tid) VALUES (%d, %d)', $nid, $tid);
+  }
+  else {
+    unset($old_terms[$tid]);
+  }
 }
 
 /**
@@ -1158,10 +1169,12 @@
      $output['taxonomy'] = taxonomy_node_get_terms($node->nid);
      return $output;
     case 'insert':
-      taxonomy_node_save($node->nid, $node->taxonomy);
+      taxonomy_node_save($node->nid, $node->taxonomy, array());
       break;
-    case 'update':
-      taxonomy_node_save($node->nid, $node->taxonomy);
+    case 'submit':
+      if ($node->nid) {
+        taxonomy_node_save($node->nid, $node->taxonomy);
+      }
       break;
     case 'delete':
       taxonomy_node_delete($node->nid);