Add get_run_count DB API function

This commit adds a new DB API function get_run_count() which, like it's
name implies, returns the number of runs in the DB.

Change-Id: I31507f2e8ee8e3cc9b4587573f3b44b3f10dffee

releasenotes/notes/add-get_run_count-api-43daafc592b929ef.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - Add a new DB API function get_runs_count() which returns the total number of
+    runs in the DB

subunit2sql/db/api.py

@@ -1671,6 +1671,17 @@ def get_recent_failed_runs_by_run_metadata(key, value, num_runs=10,
         models.Run.run_at.desc()).limit(num_runs).all()
 
 
+def get_runs_count(session=None):
+    """Get the number of runs currently in the database
+
+    :return count: The number of runs in the DB
+    :rtype: int
+    """
+    session = session or get_session()
+    query = db_utils.model_query(models.Run, session)
+    return query.count()
+
+
 def get_runs_counts_by_run_metadata(key, value, start_date=None, session=None):
     """Check runs for a given run metadata pair
 

subunit2sql/tests/db/test_api.py

@@ -909,6 +909,15 @@ class TestDatabaseAPI(base.TestCase):
         self.assertEqual(1, len(results))
         self.assertEqual(run_c.id, results[0].id)
 
+    def test_get_runs_count(self):
+        for i in range(0, 100):
+            api.create_run()
+        count = api.get_runs_count()
+        self.assertEqual(100, count)
+
+    def test_get_runs_count_zero(self):
+        self.assertEqual(0, api.get_runs_count())
+
     def test_get_runs_counts_by_run_metadata_no_start_date(self):
         run_a = api.create_run(fails=1)
         api.create_run()