launchpad-dev team mailing list archive

[Robert Collins <robert.collins@xxxxxxxxxxxxx>]

On Tue, 2010-03-02 at 11:23 -0600, Deryck Hodge wrote:
> 
> I also think it would be nice to be able to mark an attribute as
> ignorable for the sake of calculating the etag when we decorate
> attributes for exporting.  If status on a bug changes, that could
> matter to a script.  If heat changes, not so much.  Heat can't be set
> by an external script anyway.
> 
> I wonder if read_only does this or could be made to do this?  I asked
> Leonard on IRC and he wasn't sure.  He's also very busy at the moment
> to dig further into the question.  This seems a nice solution.  But it
> doesn't solve it for attributes that can be set. 

Speaking from an HTTP point of view...

derived aspects of an object that have *semantic* value should be
included in the ETag; because the ETag controls caching. Read only has
nothing to do with whether a change to a field should invalidate
caches. 

For PATCH commands, they supply If-Match to only patch the object they
think they are starting from. Its possible server side to decide that:
 - the Etag is a recent one
 - only readonly fields have been changed since that etag was issued
 - so we can accept the patch

-Rob

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