Fixed the case of values returned by the map function.

When doing multiple insert, SQLAlchemy was inserting an empty row when
rows is an empty list. Fixed this by not calling insert when there are
no rows.

datastore/store.py

@@ -236,11 +236,11 @@ def update_view(self, docs, session):
         q = t.delete().where(t.c._id.in_(ids))
         session.execute(q)
 
-        bind_params = dict((c.name, sa.bindparam(c)) for c in t.columns)
-        q = t.insert().values(**bind_params)
-
-        rows = self.map_docs(docs)
-        session.execute(q, list(rows))
+        rows = list(self.map_docs(docs))
+        if rows:
+            bind_params = dict((c.name, sa.bindparam(c)) for c in t.columns)
+            q = t.insert().values(**bind_params)
+            session.execute(q, rows)
 
     def _parse_order_by(self, order_by):
         if isinstance(order_by, list):

datastore/tests/test_store.py

@@ -61,6 +61,28 @@ def create_views(self):
 
         rows = self.ds.query("lname", lname="bar")
         assert [row['_key'] for row in rows] == ['bar']
+
+    def test_view_with_no_rows(self):
+        class NoneView(View):
+            def get_table(self, metadata):
+                return sa.Table("none_view", metadata)
+
+            def map(self, doc):
+                return []
+
+        class NoneStore(Datastore):
+            def create_views(self):
+                return {
+                    "none": NoneView()
+                }
+
+        self.ds = NoneStore("sqlite:///:memory:")
+
+        self.ds.put("foo", {"name": "Foo"})
+        self.ds.put("bar", {"name": "Bar"})
+
+        rows = self.ds.query("none")
+        assert len(rows) == 0
 
 class TestView:
     def test_parse_order_by(self):