Fixed #7698 -- Handle '0' correctly when used as the upper bound of a slice.

Based on a patch from enoksrd.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7885 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/query.py

@@ -285,10 +285,10 @@ class Query(object):
 
         # FIXME: Pull this out to make life easier for Oracle et al.
         if with_limits:
-            if self.high_mark:
+            if self.high_mark is not None:
                 result.append('LIMIT %d' % (self.high_mark - self.low_mark))
-            if self.low_mark:
+            if self.low_mark is not None:
-                if not self.high_mark:
+                if self.high_mark is None:
                     val = self.connection.ops.no_limit_value()
                     if val:
                         result.append('LIMIT %d' % val)
@@ -1381,12 +1381,12 @@ class Query(object):
         constraints. So low is added to the current low value and both will be
         clamped to any existing high value.
         """
-        if high:
+        if high is not None:
             if self.high_mark:
                 self.high_mark = min(self.high_mark, self.low_mark + high)
             else:
                 self.high_mark = self.low_mark + high
-        if low:
+        if low is not None:
             if self.high_mark:
                 self.low_mark = min(self.high_mark, self.low_mark + low)
             else:

tests/regressiontests/queries/models.py

@@ -810,5 +810,9 @@ used in lookups.
 >>> Item.objects.filter(created__in=[time1, time2])
 [<Item: one>, <Item: two>]
 
+Bug #7698 -- People like to slice with '0' as the high-water mark.
+>>> Item.objects.all()[0:0]
+[]
+
 """}