buildbucket: put_batch endpoint

appengine/cr-buildbucket/service.py

Index: appengine/cr-buildbucket/service.py
diff --git a/appengine/cr-buildbucket/service.py b/appengine/cr-buildbucket/service.py
index 0fcd66fd5548075644b44cd4ba1ea5c838f494ad..bcb17237887120944e713afe76dcd1ce1266caaf 100644
--- a/appengine/cr-buildbucket/service.py
+++ b/appengine/cr-buildbucket/service.py
@@ -135,6 +135,29 @@ class BuildBucketService(object):
         'Build %s was created by %s', build.key.id(), identity.to_bytes())
     return build
 
+  @ndb.transactional(xg=True)  # pylint: disable=no-value-for-parameter

[Vadim Sh., 2015/04/14 18:56:40]

I don't think adding them all transactionally is a good idea:
1) Weird unavoidable limit of 25.
2) It is slow, with 25 groups probably very slow (have you tried it?).

One way of not triggering already triggered builds on retry is to introduce a
new "client_operation_id" into API that server can use to identify retries. E.g.
put_batch([builds], operation_id) -> ([triggered], [existing]). Then from client
point of view put_batch(..., some client id) is essentially idempotent.

[nodir, 2015/04/14 22:13:05]

Done.

+  def add_batch(self, build_params):
+    """Adds multiple builds in a cross-group transaction.
+
+    Args:
+      build_params: list of dicts, where each dict contains parameters for
+        add() method.
+
+    Returns:
+      List of builds.
+    """
+    if len(build_params) > 25:
+      # Cross-group transactions support up to 25 entity groups.
+      raise errors.InvalidInputError('Cannot add more than 25 builds at a time')
+    builds = []
+    for i, req in enumerate(build_params):
+      try:
+        builds.append(self.add(**req))
+      except errors.Error as ex:
+        msg = 'Error in build request %d: %s' % (i, ex.message)
+        raise type(ex)(msg)
+    return builds
+
   def get(self, build_id):
     """Gets a build by |build_id|.