Allow using a metric type in the Query method select_metrics.

This is useful when a user wants to apply the exact same filters
(duration, aggregation, resource labels) for a different metric type.

monitoring/google/cloud/monitoring/query.py

@@ -297,6 +297,8 @@ def select_metrics(self, *args, **kwargs):
 
             query = query.select_metrics(instance_name='myinstance')
             query = query.select_metrics(instance_name_prefix='mycluster-')
+            query = query.select_metrics(
+                metric_type='compute.googleapis.com/instance/cpu/utilization')
 
         A keyword argument ``<label>=<value>`` ordinarily generates a filter
         expression of the form::
@@ -314,6 +316,20 @@ def select_metrics(self, *args, **kwargs):
 
             metric.label.<label> = ends_with("<value>")
 
+        As a special case, ``"metric_type"`` is treated as a special
+        pseudo-label corresponding to the filter object ``metric.type``.
+        For example, ``metric_type=<value>`` generates::
+
+            metric.type = "<value>"
+
+        See the `supported metrics`_.
+
+        .. note::
+
+            Currently, the query can only support a single metric type. Given
+            this, prefix and suffix filtering is not supported for
+            ``"metric_type"``.
+
         If the label's value type is ``INT64``, a similar notation can be
         used to express inequalities:
 
@@ -344,6 +360,8 @@ def select_metrics(self, *args, **kwargs):
 
         :rtype: :class:`Query`
         :returns: The new query object.
+
+        .. _supported metrics: https://cloud.google.com/monitoring/api/metrics
         """
         new_query = self.copy()
         new_query._filter.select_metrics(*args, **kwargs)
@@ -630,6 +648,10 @@ def select_metrics(self, *args, **kwargs):
 
         See :meth:`Query.select_metrics`.
         """
+        new_metric_type = kwargs.pop('metric_type', None)
+        if new_metric_type is not None:
+            self.metric_type = new_metric_type
+
         self.metric_label_filter = _build_label_filter('metric',
                                                        *args, **kwargs)
 

monitoring/unit_tests/test_query.py

@@ -206,13 +206,15 @@ def test_filter_by_resources(self):
 
     def test_filter_by_metrics(self):
         INSTANCE = 'my-instance'
+        NEW_METRIC_TYPE = 'compute.googleapis.com/instance/utilization'
         client = _Client(project=PROJECT, connection=_Connection())
         query = self._make_one(client, METRIC_TYPE)
-        query = query.select_metrics(instance_name=INSTANCE)
+        query = query.select_metrics(metric_type=NEW_METRIC_TYPE,
+                                     instance_name=INSTANCE)
         expected = (
             'metric.type = "{type}"'
             ' AND metric.label.instance_name = "{instance}"'
-        ).format(type=METRIC_TYPE, instance=INSTANCE)
+        ).format(type=NEW_METRIC_TYPE, instance=INSTANCE)
         self.assertEqual(query.filter, expected)
 
     def test_request_parameters_minimal(self):
@@ -522,15 +524,27 @@ def test_maximal(self):
         obj.projects = 'project-1', 'project-2'
         obj.select_resources(resource_type='some-resource',
                              resource_label='foo')
-        obj.select_metrics(metric_label_prefix='bar-')
+        obj.select_metrics(metric_type='some-metric',
+                           metric_label_prefix='bar-')
 
         expected = (
-            'metric.type = "{type}"'
+            'metric.type = "some-metric"'
             ' AND group.id = "1234567"'
             ' AND project = "project-1" OR project = "project-2"'
             ' AND resource.label.resource_label = "foo"'
             ' AND resource.type = "some-resource"'
             ' AND metric.label.metric_label = starts_with("bar-")'
+        )
+
+        self.assertEqual(str(obj), expected)
+
+    def test_select_metrics_without_type(self):
+        obj = self._make_one(METRIC_TYPE)
+        obj.select_metrics(metric_label_prefix='bar-')
+
+        expected = (
+            'metric.type = "{type}"'
+            ' AND metric.label.metric_label = starts_with("bar-")'
         ).format(type=METRIC_TYPE)
 
         self.assertEqual(str(obj), expected)