dbconfig: support the case where the db is not initialized

Instead of just crashing, return the default value or KeyError

buildbot db init code will explain how to create the tables

master/buildbot/db/dbconfig.py

@@ -16,6 +16,7 @@
 from buildbot.db import enginestrategy
 from buildbot.db import model
 from buildbot.db import state
+from sqlalchemy.exc import OperationalError
 
 
 class FakeDBConnector(object):
@@ -58,16 +59,29 @@ def getDb(self):
         db.master.caches = FakeCacheManager()
         db.model = model.Model(db)
         db.state = state.StateConnectorComponent(db)
-        self.objectid = db.state.thdGetObjectId(db_engine, self.name, "DbConfig")['id']
+        try:
+            self.objectid = db.state.thdGetObjectId(db_engine, self.name, "DbConfig")['id']
+        except OperationalError as e:
+            if "no such table" in str(e):
+                db.pool.engine.close()
+                return None
+            else:
+                raise
         return db
 
     def get(self, name, default=state.StateConnectorComponent.Thunk):
         db = self.getDb()
-        ret = db.state.thdGetState(db.pool.engine, self.objectid, name, default=default)
-        db.pool.engine.close()
+        if db is not None:
+            ret = db.state.thdGetState(db.pool.engine, self.objectid, name, default=default)
+            db.pool.engine.close()
+        else:
+            if default is not state.StateConnectorComponent.Thunk:
+                return default
+            raise KeyError("Db not yet initialized")
         return ret
 
     def set(self, name, value):
         db = self.getDb()
-        db.state.thdSetState(db.pool.engine, self.objectid, name, value)
-        db.pool.engine.close()
+        if db is not None:
+            db.state.thdSetState(db.pool.engine, self.objectid, name, value)
+            db.pool.engine.close()

master/buildbot/test/unit/test_db_dbconfig.py

@@ -68,3 +68,28 @@ def test_init2(self):
     def test_init3(self):
         obj = dbconfig.DbConfig({}, self.basedir)
         self.assertEqual(obj.db_url, "sqlite:///state.sqlite")
+
+
+class TestDbConfigNotInitialized(db.RealDatabaseMixin, unittest.TestCase):
+
+    @defer.inlineCallbacks
+    def setUp(self):
+        # as we will open the db twice, we can't use in memory sqlite
+        yield self.setUpRealDatabase(table_names=[], sqlite_memory=False)
+
+    def createDbConfig(self):
+        return dbconfig.DbConfig({"db_url": self.db_url}, self.basedir)
+
+    def test_default(self):
+        def thd():
+            db = self.createDbConfig()
+            self.assertEqual("foo", db.get(u"slaves", "foo"))
+
+        return threads.deferToThread(thd)
+
+    def test_error(self):
+        def thd():
+            db = self.createDbConfig()
+            self.assertRaises(KeyError, db.get, u"slaves")
+
+        return threads.deferToThread(thd)