Merge branch 'master' into drop_py2_support

mongoengine/queryset/base.py

@@ -56,7 +56,6 @@ class BaseQuerySet:
         self._ordering = None
         self._snapshot = False
         self._timeout = True
-        self._slave_okay = False
         self._read_preference = None
         self._iter = False
         self._scalar = []
@@ -254,16 +253,17 @@ class BaseQuerySet:
         except StopIteration:
             msg = "%s matching query does not exist." % queryset._document._class_name
             raise queryset._document.DoesNotExist(msg)
+
         try:
+            # Check if there is another match
             next(queryset)
         except StopIteration:
             return result
 
-        # If we were able to retrieve the 2nd doc, rewind the cursor and
-        # raise the MultipleObjectsReturned exception.
-        queryset.rewind()
-        message = "%d items returned, instead of 1" % queryset.count()
-        raise queryset._document.MultipleObjectsReturned(message)
+        # If we were able to retrieve the 2nd doc, raise the MultipleObjectsReturned exception.
+        raise queryset._document.MultipleObjectsReturned(
+            "2 or more items returned, instead of 1"
+        )
 
     def create(self, **kwargs):
         """Create new object. Returns the saved object instance.
@@ -769,7 +769,6 @@ class BaseQuerySet:
             "_ordering",
             "_snapshot",
             "_timeout",
-            "_slave_okay",
             "_read_preference",
             "_iter",
             "_scalar",
@@ -1020,9 +1019,11 @@ class BaseQuerySet:
 
             posts = BlogPost.objects(...).fields(comments=0)
 
-        To retrieve a subrange of array elements:
+        To retrieve a subrange or sublist of array elements,
+        support exist for both the `slice` and `elemMatch` projection operator:
 
             posts = BlogPost.objects(...).fields(slice__comments=5)
+            posts = BlogPost.objects(...).fields(elemMatch__comments="test")
 
         :param kwargs: A set of keyword arguments identifying what to
             include, exclude, or slice.
@@ -1031,7 +1032,7 @@ class BaseQuerySet:
         """
 
         # Check for an operator and transform to mongo-style if there is
-        operators = ["slice"]
+        operators = ["slice", "elemMatch"]
         cleaned_fields = []
         for key, value in kwargs.items():
             parts = key.split("__")
@@ -1164,20 +1165,6 @@ class BaseQuerySet:
         queryset._timeout = enabled
         return queryset
 
-    # DEPRECATED. Has no more impact on PyMongo 3+
-    def slave_okay(self, enabled):
-        """Enable or disable the slave_okay when querying.
-
-        :param enabled: whether or not the slave_okay is enabled
-
-        .. deprecated:: Ignored with PyMongo 3+
-        """
-        msg = "slave_okay is deprecated as it has no impact when using PyMongo 3+."
-        warnings.warn(msg, DeprecationWarning)
-        queryset = self.clone()
-        queryset._slave_okay = enabled
-        return queryset
-
     def read_preference(self, read_preference):
         """Change the read_preference when querying.
 
@@ -1952,23 +1939,3 @@ class BaseQuerySet:
         setattr(queryset, "_" + method_name, val)
 
         return queryset
-
-    # Deprecated
-    def ensure_index(self, **kwargs):
-        """Deprecated use :func:`Document.ensure_index`"""
-        msg = (
-            "Doc.objects()._ensure_index() is deprecated. "
-            "Use Doc.ensure_index() instead."
-        )
-        warnings.warn(msg, DeprecationWarning)
-        self._document.__class__.ensure_index(**kwargs)
-        return self
-
-    def _ensure_indexes(self):
-        """Deprecated use :func:`~Document.ensure_indexes`"""
-        msg = (
-            "Doc.objects()._ensure_indexes() is deprecated. "
-            "Use Doc.ensure_indexes() instead."
-        )
-        warnings.warn(msg, DeprecationWarning)
-        self._document.__class__.ensure_indexes()