You can use a unique counter for all the entities. 2**128 is a lot.
You can use a sharded counter to generate the unique id's, it uses a
transaction.
2009/4/20 Chris Spencer <chriss...@gmail.com>:
>
> Thanks, that's a good thought. I agree that it should be done in a
> transaction. However, I don't believe App Engine allows you to run
> queries in a transaction.
>
> Chris
>
> 2009/4/20 djidjadji <djidja...@gmail.com>:
>>
>> Hi Chris,
>>
>> You can do this by adding an extra attribute to the object that
>> contains the date and a sequence number.
>>
>> The extra attribute is an IntegerProperty. It has arbitrary precision,
>> unlimited bit length.
>> If you store
>> (long(datetime.toordinal(myRecord.date))<<128)+long(sequenceNum)
>> you can store a lot of entities on one date, 2**128. If you set
>> sequenceNum starting at 1 you can use your query that sets
>>
>> startDate = (long(datetime.toordinal(someDate1))<<128)+long(0)
>> endDate = (long(datetime.toordinal(someDate2))<<128)+long(0)
>> query = Record.all().filter('dateEx >', startDate).filter('dateEx <',
>> endDate)
>>
>> if you fetch 100 objects use the value of dateEx of the last object
>> retrieved as the new startDate for the next batch.
>>
>> When you store a new entity:
>> get the object with the highest value of dateEx with the same
>> ordinal value,
>> add 1L and set as the dateEx value of the new entity
>> This should be done in a transaction or some kind of "Critical
>> section" to ensure unique sequence numbers
>>
>> 2009/4/20 Chris Spencer <chriss...@gmail.com>:
>>>
>>> Thanks, but I don't see how that's relevant. Like I said, the ordering
>>> of an object's key has no correlation to an object's date.
>>>
>>> I'm not trying to simply page. That's trivial using the method listed
>>> in your link. What I'm trying to do is page through a set of objects
>>> limited by a date range.
>>>
>>> Chris
>>>
>>> 2009/4/19 秦锋 <feng.w....@gmail.com>:
>>>>
>>>> CHeck this:
>>>> http://google-appengine.googlegroups.com/web/efficient_paging_using_key_instead_of_a_dedicated_unique_property.txt?gda=7FbhWXcAAACSStSWrftt07H4FK2Rtvurv5Qi9dmYyYZMEnTZCjCsYQQgER4RQV57mxjvIzAWBZmQ3TeCdbqm30Qz_AwgYlIpRbcWRj3jGGBm-fgbnPJIYc4-hXRRmo3Xgj6KgtSLBeZ45alvcyXc30EbEX-RNDZveV4duv6pDMGhhhZdjQlNAw
>>>>
>>>> On 4月19日, 下午12时32分, Chris <chriss...@gmail.com> wrote:
>>>>> I have the model:
>>>>>
>>>>> class Record(db.Model):
>>>>> date = db.DateProperty()
>>>>>
>>>>> Over 1000 Record instances may contain the same date value. The
>>>>> instances are also not created in the order of their dates.
>>>>>
>>>>> I'm trying to query all instances whose date is within a given range.
>>>>> I need to be able to query sets larger than the default max of 1000.
>>>>>
>>>>> I was thinking of doing something like:
>>>>>
>>>>> Record.all().filter('date >', startDate).filter('date <', endDate)
>>>>>
>>>>> But this would limit me at most to the first 1000 records. How would I
>>>>> get the next 1000 records, maintaining the range query? I can't use
>>>>> the last date value from the previous query as the startDate for the
>>>>> next query, since there's no guarantee that the date value has
>>>>> changed. For example, I could have 2000 instances with the date
>>>>> 2008-1-1, so the first and second query sets have identical filter
>>>>> parameters.
>>>>>
>>>>> Intuitively, I could accomplish this by simply filtering on the
>>>>> previous key value (e.g. .filter('key >', lastKeyValue)).
>>>>> Unfortunately, App Engine currently prohibits filtering with
>>>>> inequality operators on more than one property.
>>>>>
>>>>> Am I correct in understanding that there's essentially no way to query
>>>>> all instances within a specific date range, due to this limitation?
>>>>>
>>>>> This issue keeps coming up for me, and has been a huge deal-breaker in
>>>>> a lot of potential projects I've been working on for App Engine. Any
>>>>> advice on how I could work around it would be appreciated.
>>>>>
>>>>> Chris
>>>> >
>>>>
>>
>> >
>>
>
> >
>
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