Added link() functionality to create links between related records. It basically works in the opposite way as unlink().

lib/Doctrine/Record.php

@@ -1682,6 +1682,80 @@ abstract class Doctrine_Record extends Doctrine_Record_Abstract implements Count
         return $this;
     }
 
+
+    /**
+     * link
+     * creates links from this record to given records
+     *
+     * @param string $alias     related component alias
+     * @param array $ids        the identifiers of the related records
+     * @return Doctrine_Record  this object
+     */
+    public function link($alias, array $ids)
+    {
+        if ( ! count($ids)) {
+            return $this;
+        }
+
+        $identifier = array_values($this->identifier());
+        $identifier = array_shift($identifier);
+
+        $rel = $this->getTable()->getRelation($alias);
+
+        if ($rel instanceof Doctrine_Relation_Association) {
+
+            $modelClassName = $rel->getAssociationTable()->getComponentName();
+            $localFieldName = $rel->getLocal();
+            $localFieldDef  = $rel->getAssociationTable()->getColumnDefinition($localFieldName);
+            if ($localFieldDef['type'] == 'integer') {
+                $identifier = (integer) $identifier;
+            }
+            $foreignFieldName = $rel->getForeign();
+            $foreignFieldDef  = $rel->getAssociationTable()->getColumnDefinition($foreignFieldName);
+            if ($foreignFieldDef['type'] == 'integer') {
+                for ($i = 0; $i < count($ids); $i++) {
+                    $ids[$i] = (integer) $ids[$i];
+                }
+            }
+            foreach ($ids as $id) {
+                $record = new $modelClassName;
+                $record[$localFieldName]   = $identifier;
+                $record[$foreignFieldName] = $id;
+                $record->save();
+            }
+
+        } else if ($rel instanceof Doctrine_Relation_ForeignKey) {
+
+            $q = new Doctrine_Query();
+
+            $q->update($rel->getTable()->getComponentName())
+              ->set($rel->getForeign(), '?', array_values($this->identifier()));
+
+            if (count($ids) > 0) {
+                $q->whereIn($rel->getTable()->getIdentifier(), $ids);
+            }
+
+            $q->execute();
+
+        } else if ($rel instanceof Doctrine_Relation_LocalKey) {
+
+            $q = new Doctrine_Query();
+
+            $q->update($this->getTable()->getComponentName())
+              ->set($rel->getLocal(), '?', $ids);
+
+            if (count($ids) > 0) {
+                $q->whereIn($rel->getTable()->getIdentifier(), array_values($this->identifier()));
+            }
+
+            $q->execute();
+
+        }
+
+        return $this;
+    }
+
+
     /**
      * __call
      * this method is a magic method that is being used for method overloading