A Clojure/Datomic library for idempotently transacting datoms (norms) into your database – be they schema, data, or otherwise.
In the simplest sense, conformity allows you to write schema migrations and ensure that they run once and only once.
In a more general sense, conformity allows you to declare expectations (in the form of norms) about the state of your database, and enforce those idempotently without repeatedly transacting schema, required data, etc.
Conformity is available on clojars, and can be included in your leiningen project.clj
by adding the following to :dependencies
:
The easiest way to use conformity is to store your norms in an edn file that lives in your resources/
folder.
;; resources/something.edn
{:my-project/something-schema
{:txes [[{:db/id #db/id [:db.part/db]
:db/ident :something/title
:db/valueType :db.type/string
:db/cardinality :db.cardinality/one
:db/index false
:db.install/_attribute :db.part/db}]]}}
Then in your code:
(ns my-project.something
(:require [io.rkn.conformity :as c]
[datomic.api :as d]))
(def uri "datomic:mem://my-project")
(d/create-database uri)
(def conn (d/connect uri))
(def norms-map (c/read-resource "something.edn"))
(println (str "Has attribute? " (c/has-attribute? (d/db conn) :something/title)))
(c/ensure-conforms conn norms-map [:my-project/something-schema])
(println (str "Has attribute? " (c/has-attribute? (d/db conn) :something/title)))
; ... Code dependant on the presence of attributes in :my-project/something-schema
You can see this more directly illustrated in a console…
; nREPL 0.1.5
; Setup a in-memory db
(require '[datomic.api :as d])
(def uri "datomic:mem://my-project")
(d/create-database uri)
(def conn (d/connect uri))
; Hook up conformity and your sample datom
(require '[io.rkn.conformity :as c])
(def norms-map (c/read-resource "something.edn"))
(c/has-attribute? (d/db conn) :something/title)
; -> false
(c/ensure-conforms conn norms-map [:my-project/something-schema])
(c/has-attribute? (d/db conn) :something/title)
; -> true
The {:txes [...]}
can also have a :requires
attribute, which points to the keyword/ident of some other such map which it depends on having been already transacted before it can be. This is declarative; Once specified in the map passed to ensure-conforms
, confirmity handles the rest.
Once a norm is conformed to that's it! It won't be transacted again. That does mean that you shouldn't edit a norm and expect it to magically get updated the next time ensure-conforms
runs.
In the future you may be able to intelligently version norms themselves, but I had to draw the line somewhere for the initial release.
Copyright © 2012-2014 Ryan Neufeld
Distributed under the Eclipse Public License, the same as Clojure.