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From Antony Blakey <>
Subject Re: Can I guarantee uniqueness in a field without using _id?
Date Tue, 13 Jan 2009 01:43:02 GMT

On 13/01/2009, at 11:42 AM, James Marca wrote:

> You are restricting the use of _id for this "feature" due to your
> design decision of using just integer ids.  But I don't think you can
> also complain that there is no way to guarantee the uniqueness of an
> arbitrary (set of) field(s).  There is, you're just not using it.
> Again, I haven't been using couchdb for more than two months, but I'd
> guess the developers are not going to see a need to allow for
> *another* guaranteed unique field.

Particularly given that the uniqueness of the id field is to do with  
document identity, rather than uniqueness per-se.

A fundamental issue you have to remember is that Couch is designed to  
act in a disconnected p2p fashion. Different peers can create and edit  
documents, and when they replicate you get conflicts that have to be  
handled without the benefit of any global conflict resolution. This is  
why considerations of uniqueness are a dead-end. You have to think in  
terms of document identity, and the ontological mapping of that  
identity. If identity in your domain is determined by the name you  
give something, then that should be the id, and if you use writable  
replicas then you need to handle replication conflicts. So uniqueness  
in the sense that you are looking for is just not part of Couch's big  
picture. As soon as the concept of 'lock' appears in your thinking,  
you know you're on the wrong track.

As others have said, if you want a global state you need to look for  
something outside of Couch, and that has it's own problems because  
global state in a distributed manner is dependent on connectivity.

CouchDB is so far from a relation database that even including the  
word 'database' (DB), with all of it's presumptive extensions, is  
unfortunate IMO.

Antony Blakey
CTO, Linkuistics Pty Ltd
Ph: 0438 840 787

Isn't it enough to see that a garden is beautiful without having to  
believe that there are fairies at the bottom of it too?
   -- Douglas Adams

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