diff --git a/lib/Doctrine/Hydrate.php b/lib/Doctrine/Hydrate.php
index 310d8fc24..10d3b66b6 100644
--- a/lib/Doctrine/Hydrate.php
+++ b/lib/Doctrine/Hydrate.php
@@ -91,6 +91,9 @@ class Doctrine_Hydrate extends Doctrine_Object implements Serializable
      *          parent              the alias of the parent
      *
      *          agg                 the aggregates of this component
+     *
+     *          map                 the name of the column / aggregate value this
+     *                              component is mapped to a collection
      */
     protected $_aliasMap         = array();
     /**
@@ -1034,7 +1037,20 @@ class Doctrine_Hydrate extends Doctrine_Object implements Serializable
 
             $index = $driver->search($element, $array);
             if ($index === false) {
-                $array[] = $element;
+                $key = $map['map'];
+                
+                if (isset($key)) {
+                    if (isset($array[$key])) {
+                        throw new Doctrine_Hydrate_Exception("Couldn't hydrate. Found non-unique key mapping.");
+                    }
+
+                    if ( ! isset($element[$key])) {
+                        throw new Doctrine_Hydrate_Exception("Couldn't hydrate. Found a non-existent key.");
+                    }
+                    $array[$element[$key]] = $element;
+                } else {
+                    $array[] = $element;
+                }
             }
             $this->_setLastElement($prev, $array, $index, $rootAlias, $oneToOne);
             unset($currData[$rootAlias]);
@@ -1050,7 +1066,7 @@ class Doctrine_Hydrate extends Doctrine_Object implements Serializable
                 $relation = $map['relation'];
                 $componentAlias = $map['relation']->getAlias();
 
-                if (!isset($prev[$parent])) {
+                if ( ! isset($prev[$parent])) {
                     break;
                 }
 
@@ -1065,7 +1081,19 @@ class Doctrine_Hydrate extends Doctrine_Object implements Serializable
                             $index = $driver->search($element, $prev[$parent][$componentAlias]);
 
                             if ($index === false) {
-                                $prev[$parent][$componentAlias][] = $element;
+                                $key = $map['map'];
+
+                                if (isset($key)) {
+                                    if (isset($prev[$parent][$componentAlias][$key])) {
+                                        throw new Doctrine_Hydrate_Exception("Couldn't hydrate. Found non-unique key mapping.");
+                                    }
+                                    if ( ! isset($element[$key])) {
+                                        throw new Doctrine_Hydrate_Exception("Couldn't hydrate. Found a non-existent key.");
+                                    }
+                                    $prev[$parent][$componentAlias][$element[$key]] = $element;
+                                } else {
+                                    $prev[$parent][$componentAlias][] = $element;
+                                }
                             }
                         }
                         // register collection for later snapshots
diff --git a/lib/Doctrine/Query.php b/lib/Doctrine/Query.php
index 10d575635..550894dc5 100644
--- a/lib/Doctrine/Query.php
+++ b/lib/Doctrine/Query.php
@@ -1217,6 +1217,15 @@ class Doctrine_Query extends Doctrine_Query_Abstract implements Countable
 
     public function load($path, $loadFields = true) 
     {
+    	$e = Doctrine_Tokenizer::quoteExplode($path, ' MAP ');
+
+        $mapWith = null;
+        if (count($e) > 1) {
+            $mapWith = trim($e[1]);
+            
+            $path = $e[0];
+        }
+
         // parse custom join conditions
         $e = explode(' ON ', $path);
 
@@ -1286,7 +1295,8 @@ class Doctrine_Query extends Doctrine_Query_Abstract implements Countable
                 $table    = $relation->getTable();
                 $this->_aliasMap[$componentAlias] = array('table'    => $table,
                                                           'parent'   => $parent,
-                                                          'relation' => $relation);
+                                                          'relation' => $relation,
+                                                          'map'      => null);
                 if ( ! $relation->isOneToOne()) {
                    $this->needsSubquery = true;
                 }
@@ -1405,7 +1415,16 @@ class Doctrine_Query extends Doctrine_Query_Abstract implements Countable
             }
             $parent = $prevPath;
         }
+        if (isset($mapWith)) {
+            $e = explode('.', $mapWith);
+            $table = $this->_aliasMap[$componentAlias]['table'];
+            
+            if ( ! $table->hasColumn($e[1])) {
+                throw new Doctrine_Query_Exception("Couldn't use key mapping. Column " . $e[1] . " does not exist.");                                	
+            }
 
+            $this->_aliasMap[$componentAlias]['map'] = $table->getColumnName($e[1]);
+        }
         return $this->_aliasMap[$componentAlias];
     }
 
@@ -1435,7 +1454,7 @@ class Doctrine_Query extends Doctrine_Query_Abstract implements Countable
 
         $this->parts['from'][] = $queryPart;
         $this->tableAliases[$tableAlias]  = $componentAlias;
-        $this->_aliasMap[$componentAlias] = array('table' => $table);
+        $this->_aliasMap[$componentAlias] = array('table' => $table, 'map' => null);
         
         return $table;
     }