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From Kevin Burton <>
Subject Re: Exist test?
Date Mon, 05 Nov 2012 19:57:36 GMT
So the update handler sets some global variable indicating that the document already exists?
How do I tell that the update handler has run to completion?

On Nov 5, 2012, at 1:50 PM, Mark Hahn <> wrote:

> You can use an update handler.  It works with non-existent docs.  It's a
> very clean way to do it that I use.
> On Mon, Nov 5, 2012 at 11:45 AM, Robert Newson <> wrote:
>> Easiest to just create the document, you'll get a 409 response to indicate
>> that it already existed. If your documents don't have user assigned id's,
>> then I don't see how you could check for existence before writing anyway.
>> On 5 November 2012 19:40, Kevin Burton <> wrote:
>>> I am mainly using it the context of initially populating a database. So
>>> there isn't any danger of a race because there is only one user.
>>> On Nov 5, 2012, at 12:47 PM, Jens Alfke <> wrote:
>>>> On Nov 5, 2012, at 10:22 AM, Kevin Burton <>
>>> wrote:
>>>>> I am calling CreateDocument<Document>() but I suspect that testing
>>> the document exists first may perform better in the long run. I am using
>>> DreamSeat for my driver but I suspect other drivers have a similar
>> "test".
>>> My problem is that I don't know what to test for and I am unfamiliar with
>>> the available methods. Any one successfully use such a pattern
>> (preferably
>>> with DreamSeat) that tests for existence then creates if the document
>>> doesn't exist? Keep in mind I don't initially have an id. Thank you.
>>>> I don’t know anything about that particular API, but in general,
>>> check-then-create doesn’t work well in a concurrent environment. It’s
>> prone
>>> to race conditions where something else creates the resource in between
>>> your check call and your create call. (The canonical example is checking
>>> whether a file exists, then creating the file, which is a classic old
>>> security hole in privileged Unix tools.)
>>>> —Jens

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