To answer your question more specifically... the answer is no. If you don't apply a sort order, ordering is undefined and may even change from query to query.
You can order by __key__ but there is no guarantee that keys increase monotonically. You can create your own datestamp field but keep in mind that clocks can (and will) skew between instances. The amount of skew has no guaranteed limit. So you can pretty much only guarantee ordering for put()s from a single instance, and only if you ensure that the datestamp actually increments between writes (be careful with batch puts). I've found it necessary to create my own monotonically increasing counter using memcache increment to deal with situations like this. It is a nontrivial problem. Jeff On Tue, May 17, 2011 at 4:59 PM, Erick Fleming <[email protected]> wrote: > @Brandon > You are correct, I really care about the order of the records when > retrieving them, so I guess my question should have been "Is the result > order of a query consistent with the put order". > I know I can use DateTime (or Date in Java), but I always need these > Entities in a specific order and was just trying to avoid using the sort. > Thanks for your feedback and especially the humorous example :-) > On Tue, May 17, 2011 at 6:31 PM, Brandon Wirtz <[email protected]> wrote: >> >> Order often matters. (I don't know about the context of this app) >> >> Say you are 4th Bank Of Brandon >> >> You process transactions from your customer Strom >> >> Strom has $500 in his account. >> >> Strom hits the Che Target for $450, Cylon's Coffee Shop for $6, the Hair >> Stylist for $50, and Google bills him for each of his for App Engine >> Accounts at $9 each. >> >> Because of the way the bank does caching Strom could make any purchase in >> a >> 4 hour window up to $600 ($500 plus his $100 overdraft protection) >> >> If we process the charges in the above order, 4BoB charges Strom $35 over >> draft on the last 5 trans actions. >> If we process the charges in the reverse order 4BoB only gets one over >> draft. >> Depending on the order you can have anywhere from 1 to 6 overdrafts when >> the >> daily fee assessment task runs and determines how much Strom owes. >> >> Yes if we put the time stamp in it shouldn't matter which order the items >> were added to the table... Which is likely the bit that Erick needed. >> (BTW >> Erick you are both Eric with a C and a K so I'd have thought you'd have >> gotten the redundancy I'm going to explain next... >> >> When you store data that will need to be ordered add the auto DateTime to >> it. Or the Time the thing took place, like my bank example someone may >> have >> made a purchase on Tuesday that doesn't show up until Thursday and you'd >> want both when you got the transaction and when it happened. >> >> Then sort the returned date by the DateTime, (or that other time thing we >> just discussed) then do whatever you were going to do with the data. >> >> Don't do this... >> >> Strom has >> >> $500 >> -450 >> = 50 >> >> Google sends 4 requests for $9 in 3 seconds >> >> 50-9 = 41 >> 50-9=41 >> 41-9=32 >> 32-9=23 >> >> And you missed $9 because you processed each trans action rather than >> batching a lot of transactions but only using data older than a certain >> amount, and without flagging said data as "processed". >> >> >> >> >> >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of Strom >> Sent: Tuesday, May 17, 2011 3:55 PM >> To: Google App Engine >> Subject: [google-appengine] Re: Is the order of datastore puts guaranteed? >> >> First, the context needs to be a transaction, otherwise there isn't even a >> guarantee that all puts will happen. >> Even inside a transaction though, why does the order matter? I can only >> think of a situation where you use system generated ids, but those aren't >> guaranteed to be in order anyway. >> >> On May 17, 10:02 pm, Erick Fleming <[email protected]> wrote: >> > Within the context of an Entity group, can I guarantee that puts will >> > be in the order I put them? >> > >> > Thanks >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Google App Engine" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> http://groups.google.com/group/google-appengine?hl=en. >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Google App Engine" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> http://groups.google.com/group/google-appengine?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. 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