Your understanding is correct based on my experience.  As far as
determining entity group I think you'll just have to examine the
ancestry  of each entity in your transaction to see if they actually
have a common instance.

On Sep 25, 11:33 pm, Jamesz <[EMAIL PROTECTED]> wrote:
> Hi everyone,
>
> I just want to check my general understanding of app engine datastore
> concepts with you guys.
>
> After reading documentations on entity group and transactions, my
> understanding is that entities of different kind can still be in the
> same group provided that they have the same ancestors(parents or
> parents of parents). This means I can perform transactions on entities
> of different kinds.
>
> For clarity, this is my understanding of app engine concepts that
> roughly translates to its RDBMS equivalent
> 1. Kind = Table (this is roughly the case, though entities of the same
> kind doesn't have to have the same fields)
> 2. Property = Field
> 3. Entity = A record
> 4. Parent and Ancestors = no equivalent but is used to group entities
> into a entity group which will be stored in the same nodes which
> enables transactional executions.
>
> But when i applied this in practice, I get an error with "Cannot
> operate on different entity groups in a transaction". So I wonder if
> I've misunderstood something, Is there a way to check what entity
> group an entity actually belongs to?
>
> Thanks
>
> James
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