Simple template expansion meta-definitions for Datomic

preprocess-schema.clj

(defn preprocess-schema
  ([schema] (preprocess-schema schema (atom {})))

  ([schema templates]
    (let [entries (transient [])
          extract-entry (fn [entry]
                          (let [template (:meta/template entry)
                                templates (:meta/templates entry)
                                entry (dissoc entry :meta/template :meta/templates)]
                            [entry (if template
                              (concat [template] templates)
                              templates)]))
          process-entry (fn [entry]
                          (let [[entry entry-templates] (extract-template-definitions entry)]
                            (merge (apply merge (map @templates entry-templates)) entry)))]
      (doseq [entry schema]
        (let [entry (process-entry entry)]
          (if-let [template-name (:meta/def-template entry)]
            (swap! templates assoc template-name (dissoc entry :meta/def-template))
            (conj! entries entry))))
      (persistent! entries))))

schema.edn

[

 ;; meta templates

 {:meta/def-template :string-column
  :db/valueType :db.type/string
  :db/cardinality :db.cardinality/one
  :db.install/_attribute :db.part/db}

 {:meta/def-template :ref-column
  :db/valueType :db.type/ref
  :db/cardinality :db.cardinality/one
  :db.install/_attribute :db.part/db}

 {:meta/def-template :identity
  :db/index true
  :db/unique :db.unique/value}

 {:meta/def-template :id-column
  :meta/templates [:string-column :identity]}

  ;; Sessions

  {:db/id #db/id[:db.part/db]
   :db/ident :db.part/sysdea-sessions
   :db.install/_partition :db.part/db}

  {:meta/template :id-column
   :db/id #db/id[:db.part/db]
   :db/ident :session/id
   :db/doc "A session's ID."
   :db/noHistory true}

  {:meta/template :ref-column
   :db/id #db/id[:db.part/db]
   :db/ident :session/user
   :db/doc "Which user the session is associated with, if any."
   :db/noHistory true}

  {:meta/template :string-column
   :db/id #db/id[:db.part/db]
   :db/ident :session/metadata
   :db/doc "Any additional information needed on the session."
   :db/noHistory true}

]

Accidentally anonymous, oops, see https://gist.github.com/4387703