BTW, this is to do "Optimistic Locking for REST", for cases like this:
Both Client A and Client B ask for the same data:
--> GET /some/data.json HTTP/1.1
<-- Date: 25 May 2011 14:00:00 GMT
<-- HTTP/1.1 200 Ok
<-- Last-Modified: 25 May 2011 13:02:30 GMT
<-- Expires: 25 May 2011 15:00:00 GMT
<-- { someData }
Client A send an update:
--> PUT /some/data.json HTTP/1.1
--> If-Unmodified-Since: 25 May 2011 13:02:30 GMT
{ someAttribute: 'blabla from client A', id: 1, type: 'SomeEntity' }
-----> Last-Modified on the representation before the update is 25 May 2011
13:02:30 GMT, so we are good to go <-----
<-- HTTP/1.1 200 OK
<-- Last-Modified: 25 May 2011 14:05:30 GMT
<-- { someData }
Client B send an update:
--> PUT /some/data.json HTTP/1.1
--> If-Unmodified-Since: 25 May 2011 13:02:30 GMT
{ someAttribute: 'blabla from client B', id: 1, type: 'SomeEntity' }
-----> BUSTED! Last-Modified on the representation is now 25 May 2011 14:05:30
because of Client A update! <-----
<-- HTTP/1.1 412 Precondition Failed
<-- { error: 'Ya man, someone before you updated the same object' }
> Errest should be using some new method on the rest delegate probably, whose
> default impl is to check for that interface on the object and then fall back
> to something hashcodey
>
> Sent from my iPhone
>
> On May 25, 2011, at 2:14 PM, Pascal Robert <[email protected]> wrote:
>
>> Ah, ERCStamped is fantastic for generating the Last-Modified header! Some
>> day, I will have two weeks off just to look at all the stuff in Wonder...
>>
>>> there's not a direct simple way to do it ... probably grab the snapshot off
>>> the EO and compute a hash of the values (you can ignore the keys because
>>> they're fixed). it might be something where you can make a new interface in
>>> ERX that your EO's could implement to provide a more optimal impl (like
>>> ERCStamped could use its lastModified as a basis).
>>>
>>> ms
>>>
>>> On May 25, 2011, at 1:55 PM, Pascal Robert wrote:
>>>
>>>> I'm trying to find a way to generate a HTTP ETag for EOs so that caching
>>>> can be done for REST services. What I want to do is to have the same ETag
>>>> value for each representation of the EO, so when one of the values change,
>>>> the ETag value will also change, but if the EO have the same value, it
>>>> will generate the same ETag as another request got.
>>>>
>>>> Problem is: I don't know what to use. I tried with myEO.hashCode() but I
>>>> did some tests and every time I fetch the EO, the hashcode is different
>>>> even if the data didn't change. I'm thinking of doing a MD5 digest of part
>>>> of the EO, but I was wondering if another way exist? I could use a "last
>>>> modified" date and generate a MD5 of that too, but that date is a better
>>>> option for the Last-Modified header.
>>>>
>>>> --
>>>> Pascal Robert
>>>> [email protected]
>>>>
>>>> WOWODC 2011 : July 1-2-3, Montreal. wowodc.com
>>>>
>>>> AIM/iChat : MacTICanada
>>>> LinkedIn : http://www.linkedin.com/in/macti
>>>> Twitter : pascal_robert
>>>>
>>>>
>>>>
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>>
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