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From David Richardson <techni...@enquora.com>
Subject Re: Document validation involving other documents
Date Mon, 25 Jan 2010 01:28:02 GMT
> I'm wary of the procedural-controller middleware approach because I'm
> afraid it encourages you to program as though you have transactions.
> (Eg: change these 4 documents at the same time and hope for the best.)
I fear I haven't communicated the usage case adequately.
We're talking about validating a single document using a formula which depends on data residing
in one of several documents already in the database. Think rates, crew lists, technical abbreviations,
prior documents. We aren't changing anything on either the incoming document or the data documents
used for validation.
Simply determining whether the state of the incoming document is valid.
The validating data *could* be compiled into the validation function, but that function would
need to be updated every time the validation data changes. Possible, but inelegant.

> If you are careful with asynchronous handlers, you can be careful to
> pass the state through the database _changes feeds in a way that
> doesn't give devs a false sense of multi-document transactions.
If we don't validate and communicate failures back to author during the request/response cycle,
we may lose the chance to do so for a week or more. It also has financial implications - I've
seen documents worth $ 75,000 in billings that could not be processed for an extra week until
things were straightened out.
It gets tiresome in a hurry.

The documents arrive from clients that are usually not connected to the internet. This is
the common state of affairs in the mobile world.
By definition an asynchronous handler is outside the request/response cycle, so the communication
opportunity is lost. Additionally, the validation process is no longer atomic. If that is
the eventual path, I'll hitch this wagon to a proper message broker/transaction manager any
day.

This is exactly the usage scenario WebMachine was designed for, methinks. I've seen sporadic
references to webmachine in couchdb, including one last week I thought.
Is anything happening there? 

cheers,
David

p.s. I hope this is of some interest to other people. I hear there's been a recent small uptick
in network activity by mobile clients on unreliable, non-homogeneous networks ;-)
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