added .select method

mongoengine/queryset.py

@@ -314,6 +314,27 @@ class QueryFieldList(object):
     def __nonzero__(self):
         return bool(self.fields)
 
+class SelectResult(object):
+    """
+    Used for .select method in QuerySet
+    """
+    def __init__(self, cursor, fields):
+        self._cursor = cursor
+        self._fields = fields
+
+    def next(self):
+        try:
+            data = self._cursor.next()
+            return [data.get(f) for f in self._fields]
+        except StopIteration, e:
+            self.rewind()
+            raise e
+
+    def rewind(self):
+        self._cursor.rewind()
+
+    def __iter__(self):
+        return self
 
 class QuerySet(object):
     """A set of results returned from a query. Wraps a MongoDB cursor,
@@ -548,33 +569,38 @@ class QuerySet(object):
             cursor_args['fields'] = self._loaded_fields.as_dict()
         return cursor_args
 
+    def _build_cursor(self, **cursor_args):
+        obj = self._collection.find(self._query,
+                                    **cursor_args)
+            # Apply where clauses to cursor
+        if self._where_clause:
+            obj.where(self._where_clause)
+
+        # apply default ordering
+        if self._ordering:
+            obj.sort(self._ordering)
+        elif self._document._meta['ordering']:
+            self._ordering = self._get_order_key_list(
+                *self._document._meta['ordering'])
+            obj.sort(self._ordering)
+            
+        if self._limit is not None:
+            obj.limit(self._limit)
+            
+        if self._skip is not None:
+            obj.skip(self._skip)
+            
+        if self._hint != -1:
+            obj.hint(self._hint)
+
+        return obj
+
     @property
     def _cursor(self):
         if self._cursor_obj is None:
-
-            self._cursor_obj = self._collection.find(self._query,
-                                                     **self._cursor_args)
-            # Apply where clauses to cursor
-            if self._where_clause:
-                self._cursor_obj.where(self._where_clause)
-
-            # apply default ordering
-            if self._ordering:
-                self._cursor_obj.sort(self._ordering)
-            elif self._document._meta['ordering']:
-                self.order_by(*self._document._meta['ordering'])
-
-            if self._limit is not None:
-                self._cursor_obj.limit(self._limit)
-
-            if self._skip is not None:
-                self._cursor_obj.skip(self._skip)
-
-            if self._hint != -1:
-                self._cursor_obj.hint(self._hint)
-
+            self._cursor_obj = self._build_cursor(**self._cursor_args)
+        
         return self._cursor_obj
-
     @classmethod
     def _lookup_field(cls, document, parts):
         """Lookup a field based on its attribute and return a list containing
@@ -803,6 +829,16 @@ class QuerySet(object):
         doc.save()
         return doc
 
+    def select(self, *fields):
+        """
+        Select a field and make a tuple of element
+        """
+        cursor_args = self._cursor_args
+        cursor_args['fields'] = self._fields_to_dbfields(fields)
+        cursor = self._build_cursor(**cursor_args)
+
+        return SelectResult(cursor, fields)
+
     def first(self):
         """Retrieve the first object matching the query.
         """
@@ -1163,13 +1199,9 @@ class QuerySet(object):
             ret.append(field)
         return ret
 
-    def order_by(self, *keys):
-        """Order the :class:`~mongoengine.queryset.QuerySet` by the keys. The
-        order may be specified by prepending each of the keys by a + or a -.
-        Ascending order is assumed.
-
-        :param keys: fields to order the query results by; keys may be
-            prefixed with **+** or **-** to determine the ordering direction
+    def _get_order_key_list(self, *keys):
+        """
+        Build order list for query
         """
         key_list = []
         for key in keys:
@@ -1186,6 +1218,18 @@ class QuerySet(object):
                 pass
             key_list.append((key, direction))
 
+        return key_list
+
+    def order_by(self, *keys):
+        """Order the :class:`~mongoengine.queryset.QuerySet` by the keys. The
+        order may be specified by prepending each of the keys by a + or a -.
+        Ascending order is assumed.
+
+        :param keys: fields to order the query results by; keys may be
+            prefixed with **+** or **-** to determine the ordering direction
+        """
+        
+        key_list = self._get_order_key_list(*keys)
         self._ordering = key_list
         self._cursor.sort(key_list)
         return self