Allow class member values in projection and distinct queries (#214)

Cloud datastore needs projection and distinct properties to be strings.  This commit sets the converted properties so they may be used by the rest of the query. (Fixes #212)

google/cloud/ndb/query.py

@@ -1406,7 +1406,8 @@ def __init__(
                     "projection must be a tuple, list or None; "
                     "received {}".format(projection)
                 )
-            self._check_properties(self._to_property_names(projection))
+            projection = self._to_property_names(projection)
+            self._check_properties(projection)
             self.projection = tuple(projection)
 
         if distinct_on is not None and group_by is not None:
@@ -1426,7 +1427,8 @@ def __init__(
                     "distinct_on must be a tuple, list or None; "
                     "received {}".format(distinct_on)
                 )
-            self._check_properties(self._to_property_names(distinct_on))
+            distinct_on = self._to_property_names(distinct_on)
+            self._check_properties(distinct_on)
             self.distinct_on = tuple(distinct_on)
 
     def __repr__(self):

tests/unit/test_query.py

@@ -1165,6 +1165,44 @@ def test_constructor_with_ancestor_parameterized_thing():
         query = query_module.Query(ancestor=query_module.ParameterizedThing())
         assert isinstance(query.ancestor, query_module.ParameterizedThing)
 
+    @staticmethod
+    @pytest.mark.usefixtures("in_context")
+    @unittest.mock.patch("google.cloud.ndb.query._datastore_query")
+    def test_constructor_with_class_attribute_projection(_datastore_query):
+        class Foo(model.Model):
+            string_attr = model.StringProperty()
+
+        class Bar(model.Model):
+            bar_attr = model.StructuredProperty(Foo)
+
+        query = Bar.query(projection=[Bar.bar_attr.string_attr])
+
+        assert query.projection[0] == ("bar_attr.string_attr",)[0]
+
+        query.fetch()
+
+    @staticmethod
+    @pytest.mark.usefixtures("in_context")
+    @unittest.mock.patch("google.cloud.ndb.query._datastore_query")
+    def test_constructor_with_class_attribute_projection_and_distinct(
+        _datastore_query
+    ):
+        class Foo(model.Model):
+            string_attr = model.StringProperty()
+
+        class Bar(model.Model):
+            bar_attr = model.StructuredProperty(Foo)
+
+        query = Bar.query(
+            projection=[Bar.bar_attr.string_attr],
+            distinct_on=[Bar.bar_attr.string_attr],
+        )
+
+        assert query.projection[0] == ("bar_attr.string_attr",)[0]
+        assert query.distinct_on[0] == ("bar_attr.string_attr",)[0]
+
+        query.fetch()
+
     @staticmethod
     @pytest.mark.usefixtures("in_context")
     def test_constructor_with_projection():