denormalized-invariants

Maintain invariants
-------------------

The goal of this module is to help maintain invariants in a set of databases.
This is typically used to enforce business rules inside a database or between databases.

Specifically it is targeted at CouchDB.

``coffeescript
{invariant,DenormalizedDB} = require 'denormalized-invariants'

class Business
@Subscription: ({type}) -> type is 'subscription'

constructor: (db_uri) ->
@db = new DenormalizedDB db_uri

invariant 'A subscription document should have a panel link', @db, (S) =>
S
.filter Business.Subscription
.map (doc) =>
url = "#{panel}/s/#{doc.s}"

return if doc.panel?.url is url
doc.panel ?= {}
doc.panel.url = url
await @db.put doc
return

invariant.start()
return
``

These are called invariants because the goal of the operative part of the invariant is to attempt to maintain its textual description.