Simplify Zookeeper change cache API

Move common methods to AbstractChangeCache so that concrete
implementations only need to defined the mapping from change type as
string to the change class.

Change-Id: I78c1bdfad1c0986aa6aef387424ea35b6c2aa71d

tests/unit/test_zk.py

@@ -1243,12 +1243,6 @@ class DummyChangeCache(AbstractChangeCache):
         "DummyChange": DummyChange,
     }
 
-    def _getChangeClass(self, change_type):
-        return self.CHANGE_TYPE_MAP[change_type]
-
-    def _getChangeType(self, change):
-        return type(change).__name__
-
 
 class DummySource:
 

zuul/driver/gerrit/gerritconnection.py

@@ -63,12 +63,6 @@ class GerritChangeCache(AbstractChangeCache):
         "GerritChange": GerritChange,
     }
 
-    def _getChangeClass(self, change_type):
-        return self.CHANGE_TYPE_MAP[change_type]
-
-    def _getChangeType(self, change):
-        return type(change).__name__
-
 
 class GerritChangeData(object):
     """Compatability layer for SSH/HTTP

zuul/driver/git/gitconnection.py

@@ -34,12 +34,6 @@ class GitChangeCache(AbstractChangeCache):
         "Branch": Branch,
     }
 
-    def _getChangeClass(self, change_type):
-        return self.CHANGE_TYPE_MAP[change_type]
-
-    def _getChangeType(self, change):
-        return type(change).__name__
-
 
 class GitConnection(ZKChangeCacheMixin, BaseConnection):
     driver_name = 'git'

zuul/driver/github/githubconnection.py

@@ -103,12 +103,6 @@ class GithubChangeCache(AbstractChangeCache):
         "PullRequest": PullRequest,
     }
 
-    def _getChangeClass(self, change_type):
-        return self.CHANGE_TYPE_MAP[change_type]
-
-    def _getChangeType(self, change):
-        return type(change).__name__
-
 
 class GithubRequestLogger:
 

zuul/driver/gitlab/gitlabconnection.py

@@ -51,12 +51,6 @@ class GitlabChangeCache(AbstractChangeCache):
         "MergeRequest": MergeRequest,
     }
 
-    def _getChangeClass(self, change_type):
-        return self.CHANGE_TYPE_MAP[change_type]
-
-    def _getChangeType(self, change):
-        return type(change).__name__
-
 
 class GitlabEventConnector(threading.Thread):
     """Move events from Gitlab into the scheduler"""

zuul/driver/pagure/pagureconnection.py

@@ -107,12 +107,6 @@ class PagureChangeCache(AbstractChangeCache):
         "PullRequest": PullRequest,
     }
 
-    def _getChangeClass(self, change_type):
-        return self.CHANGE_TYPE_MAP[change_type]
-
-    def _getChangeType(self, change):
-        return type(change).__name__
-
 
 class PagureEventConnector(threading.Thread):
     """Move events from Pagure into the scheduler"""

zuul/zk/change_cache.py

@@ -286,12 +286,18 @@ class AbstractChangeCache(ZooKeeperSimpleBase, Iterable, abc.ABC):
     def _updateChange(self, change, data):
         change.deserialize(data["change_data"])
 
-    @abc.abstractmethod
     def _getChangeClass(self, change_type):
         """Return the change class for the given type."""
-        pass
+        return self.CHANGE_TYPE_MAP[change_type]
 
-    @abc.abstractmethod
     def _getChangeType(self, change):
         """Return the change type as a string for the given type."""
+        return type(change).__name__
+
+    @abc.abstractproperty
+    def CHANGE_TYPE_MAP(self):
+        """Return a mapping of change type as string to change class.
+
+        This property cann also be defined as a class attribute.
+        """
         pass