I try to figure out how easy it is to ruin/break the data in app
engine's datastore by accident. Assume that a class, say MyClass, has
a number of "persistent" members, e.g.
   ...
   int a
   int b
   int c
   ...
and assume a number of MyClass objects have been stored in app
engine's persistent storage. Now, what will happen if...

   1) a new persistent member variable, int d, is *added* to MyClass?
The old objects in datastore did not have this variable, so what will
their d-value be when they are fetched from datastore?

   2) a persistent member variable, int b, is *removed* from MyClass?
I guess the b field will be removed from all stored MyClass objects?
If not, what will happen if b is re-added at some later point in time?
Will the stored MyClass objects now get their old b-value back?

   3) the type of a persistent member variable is changed, e.g. if a
is converted to a String? What will the value of a be when the already
stored objects are fetched from datastore?

Hope someone knows the answers out there. :-)

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