Implementing constraints in couchrest-model

[Sam Wilder]

What is the best practice in CouchDB domain for implementing something
like a unique constraint. I could do this with the _id , but what if
I want to implemnet it on multiple fields, not necesarily as a
composite, but even separately. Say for e.g. I want email ID and the
username both to be unique, just to point out an example.
Is there a best practice around doing thsi without using the _id field.

[Samuel Lown]

IMHO, the current best practice is to avoid it if at all possible :-)

By design you data could be coming from anywhere, at any point in time (replication) so unique constraints are not really practical, even with the _id field.

Having said that, couchrest_model's validates_uniqueness_of should work for most simple cases where there is a low probability of collision (two users with the same email address is not likely.)

More info: http://www.couchrest.info/model/validations.html

Its not documented yet, but you can also do "scoped" validations:

validates_uniqueness_of :title, :scope => :parent_id

This would use the view "by_parent_id_and_title" to check for existing matches.

Hope that helps,

Cheers,

sam

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