You could use transactions if all Servers are in the same entity
group. In a transaction you can query for existing A specifying the
ancestor in the query. When you find no other Server with the key you
can store it - also with the same ancestor - then commit the
transaction. If another request saved the same key in between an
exception would be thrown so you could try another key.
On 17 Feb 2010, at 11:58, smile laugh wrote:
hello everyone
I have several fields which must be unique because of business
logic.how can app engine make the unique key for the several fields?
For example, in a Server "A" ,I query a value and find there is no
existing value , so I insert value into Server "A" successfully.
But almost the same time , another one can do the same thing(insert
the same record) successfully in Server "B".
Because at this time , Server "A" and Server "B" are not consistent,
the prior inserts will all be successful.
how can I avoid to insert the same records?
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