how to use 'appcfg.cmd update' without losing my json data??

```
What steps will reproduce the problem?
1. appcfg.cmd update
2. after that all existing Json data is lost
3. how can I update my new version without losing my data?



```

Original issue reported on code.google.com by `Lou.emme...@gmail.com` on 8 May 2012 at 7:37
