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From Damien Katz <>
Subject Re: A question about attachments, stubs, and revpos
Date Wed, 23 Jun 2010 17:29:38 GMT

On Jun 23, 2010, at 10:24 AM, Caleb Land wrote:

> I'm writing a CouchDB library for ruby (who isn't these days :)), partly for
> my own use, and partly to teach myself about how couch works, and play with
> some ideas I have about working with it.
> I've begun to implement attachments, and I'm a bit stuck about how to go
> forward.
> Basically, I want to know how I can:
> 1) GET a document and store it in an object
> 2) PUT an attachment to that document
> 3) PUT that document with revised fields
> The problem is, when I PUT the attachment, the document is updated and the
> new document rev is returned. I can easily stuff this rev into the _rev
> field of my local document (like everyone does when they PUT a document...
> so subsequent PUTs use the correct _rev), but the problem comes when I need
> to PUT the document, and that document doesn't have the stub for the newly
> uploaded attachment.
> I asked this question on IRC and got a reasonable answer back: Don't modify
> a document twice in a row without fetching it in between.
> This makes sense, but then I thought about how when we save documents, we
> update our local copy's _rev with the rev returned by the server so we
> wouldn't have to fetch it again.
> Also, if the local document has some other fields that have changed (let's
> say so that we could do validation before uploading the attachments), then
> we have problems.
> I can see two options to handle this:
> 1) fetch the document again and grab the _attachments and find the new
> attachment and merge it in with the local document
> 2) build a stub and inject it into the local document:
> {
>  'stub': true,
>  'revpos': parseInt(return_from_attachment_put['rev']) // *
> }

I'd use the second option, though I'm pretty sure you don't need the revpos for a stub, so
just leave that out and it should be fine.


> * I'm not sure about this, since I didn't see a formal definition for
> 'revpos' anywhere, but this seems to be how it works
> My question is, what would an experienced CouchDB developer do in this
> situation?
> -- 
> Caleb Land

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