Add DBError to _is_nested_instance

Add support for oslo.db's DBError to is_nested_instance
so we can check for IntegrityErrors in DBErrors easily
that come back from oslo.db.

This will enable the patch that depends on this to detect
port creation/network delete races very easily and retry
them.

Change-Id: I617f2549caced6547d478caba968710ad8f913b3

neutron/db/api.py

@@ -185,9 +185,13 @@ def reraise_as_retryrequest(f):
 
 def _is_nested_instance(e, etypes):
     """Check if exception or its inner excepts are an instance of etypes."""
-    return (isinstance(e, etypes) or
-            isinstance(e, exceptions.MultipleExceptions) and
-            any(_is_nested_instance(i, etypes) for i in e.inner_exceptions))
+    if isinstance(e, etypes):
+        return True
+    if isinstance(e, exceptions.MultipleExceptions):
+        return any(_is_nested_instance(i, etypes) for i in e.inner_exceptions)
+    if isinstance(e, db_exc.DBError):
+        return _is_nested_instance(e.inner_exception, etypes)
+    return False
 
 
 @contextlib.contextmanager

neutron/tests/unit/db/test_api.py

@@ -36,6 +36,11 @@ class TestExceptionToRetryContextManager(base.BaseTestCase):
             with db_api.exc_to_retry((ValueError, TypeError)):
                 raise TypeError()
 
+    def test_translates_DBerror_inner_exception(self):
+        with testtools.ExpectedException(db_exc.RetryRequest):
+            with db_api.exc_to_retry(ValueError):
+                raise db_exc.DBError(ValueError())
+
     def test_passes_other_exceptions(self):
         with testtools.ExpectedException(ValueError):
             with db_api.exc_to_retry(TypeError):