Reset primary key back to 1 after deleting all revisions

This PS resets the primary key for each table in the
database back to 1 after deleting all revisions
(i.e. DELETE /revisions) which effectively purges all
the data in the database.

Change-Id: Id64e01ea85d7098e261a56cf9eacdcce716b1f48

deckhand/db/sqlalchemy/api.py

@@ -607,15 +607,28 @@ def revision_get_all(session=None, **filters):
     return result
 
 
-def revision_delete_all(session=None):
-    """Delete all revisions.
+def revision_delete_all():
+    """Delete all revisions and resets primary key index back to 1 for each
+    table in the database.
+
+    .. warning::
+
+        Effectively purges all data from database.
 
     :param session: Database session object.
     :returns: None
     """
-    session = session or get_session()
-    session.query(models.Revision)\
-        .delete(synchronize_session=False)
+    engine = get_engine()
+    if engine.name == 'postgresql':
+        # NOTE(fmontei): While cascade should delete all data from all tables,
+        # we also need to reset the index to 1 for each table.
+        for table in ['buckets', 'revisions', 'revision_tags', 'documents',
+                      'validations']:
+            engine.execute(
+                text("TRUNCATE TABLE %s RESTART IDENTITY CASCADE;" % table)
+                .execution_options(autocommit=True))
+    else:
+        raw_query("DELETE FROM revisions;")
 
 
 def _exclude_deleted_documents(documents):

deckhand/tests/unit/db/test_revisions.py

@@ -132,8 +132,7 @@ class TestRevisions(base.TestDbBase):
         all_revision_ids = []
 
         for _ in range(3):
-            document_payload = [base.DocumentFixture.get_minimal_fixture()
-                                for _ in range(3)]
+            document_payload = [base.DocumentFixture.get_minimal_fixture()]
             bucket_name = test_utils.rand_name('bucket')
             created_documents = self.create_documents(
                 bucket_name, document_payload)
@@ -156,6 +155,13 @@ class TestRevisions(base.TestDbBase):
             self.assertRaisesRegex(errors.DocumentNotFound, error_re,
                                    self.show_document, **filters)
 
+        # Validate that the revision/document ID was reset back to 1.
+        bucket_name = test_utils.rand_name('bucket')
+        created_documents = self.create_documents(
+            bucket_name, [base.DocumentFixture.get_minimal_fixture()])
+        self.assertEqual(1, created_documents[0]['revision_id'])
+        self.assertEqual(1, created_documents[0]['id'])
+
     def test_revision_history_multiple_buckets(self):
         documents = base.DocumentFixture.get_minimal_fixture()
         alt_documents = base.DocumentFixture.get_minimal_fixture()