トランザクション エラー Nested transactions are not supported.

１.　get_or_insert 　自体がトランザクションなのでこれを含めたトランザクションを
　　作成しようとするとエラーとなる。

File "C:\Program Files\Google\google_appengine\google\appengine\api\datastore.py",
　　 line 1386, in RunInTransaction'Nested transactions are not supported.')
BadRequestError: Nested transactions are not supported.

http://code.google.com/appengine/docs/datastore/transactions.html

２．動作確認

http://googleappengine.blogspot.com/2008/08/couple-datastore-updates.html

First up is batch writes. You can now include entities in different entity groups in a single db.put() or db.delete() call. Entity modifications are only atomic within each entity group, but a single call that spans entity groups will be more efficient than a call for each group, which was required before.

以下は　SDK だと　Cannot operate on different entity groups in a transaction:
となるが Cloud では動作した。

    class Dummy2(db.Model):
      d1 = db.StringProperty()
 
    class Dummy(db.Model):
      d1 = db.StringProperty()
 
    def tran():
      d2  = Dummy2(d1 = "aaab")
      d1  = Dummy(d1 = "aaab")
 
      d1.put()
      d2.put()

    tran()

３．　その他

　　　トランザクションの中で検索は実行できない。

　　Can't query inside a transaction