Merge pull request #47 from zopefoundation/do3cc_fix_for45_master

Do3cc fix for45 master

CHANGES.rst

@@ -15,6 +15,10 @@
 
 - Add support for Python 3.5.
 
+- Avoid failure during cleanup of nested databases that provide MVCC
+  on storage level (Relstorage).
+  https://github.com/zopefoundation/ZODB/issues/45
+
 4.2.0 (2015-06-02)
 ==================
 

src/ZODB/Connection.py

@@ -1085,6 +1085,7 @@ class Connection(ExportImport, object):
     def _release_resources(self):
         for c in six.itervalues(self.connections):
             if c._mvcc_storage:
+                if c._storage is not None:
                     c._storage.release()
             c._storage = c._normal_storage = None
             c._cache = PickleCache(self, 0, 0)

src/ZODB/tests/testMVCCMappingStorage.py

@@ -33,6 +33,15 @@ from ZODB.tests import (
     )
 
 class MVCCTests:
+    def checkClosingNestedDatabasesWorks(self):
+        # This tests for the error described in
+        # https://github.com/zopefoundation/ZODB/issues/45
+        db1 = DB(self._storage)
+        db2 = DB(None, databases=db1.databases, database_name='2')
+        db1.open().get_connection('2')
+        db1.close()
+        db2.close()
+
 
     def checkCrossConnectionInvalidation(self):
         # Verify connections see updated state at txn boundaries.