Simple template expansion meta-definitions for Datomic

preprocess-schema.clj

(defn extract-key [m k]
  (when-let [value (k m)] [(dissoc m k) value]))

(defn expand-entry-id [entry]
  (if (keyword? (:db/id entry))
    (update-in entry [:db/id] d/tempid)
    entry))

(defn expand-schema-entry [entry templates]
  (if (and (map? entry) (:meta/templates entry))
    (let [[entry template-refs] (extract-key entry :meta/templates)]
      (merge (apply merge (map templates template-refs)) entry))
    entry))

(defn preprocess-schema
  ; If passed a set of entries, return a processed set of entries
  ; Otherwise expect a {:schema :templates} map.
  ([schema]
    (if (map? schema)
      (preprocess-schema (:schema schema :templates schema))
      (:schema (preprocess-schema schema {}))))

  ([schema templates]
    (reduce
      (fn [res entry]
        (let [entry (expand-schema-entry entry (:templates res))]
          (if-let [[templ templ-name] (extract-key entry :meta/def-template)]
            (update-in res [:templates] assoc templ-name templ)
            (update-in res [:schema] conj (expand-entry-id entry)))))
      {:schema [] :templates {}}
      schema)))

schema.edn

[

 ;; meta templates

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

 {:meta/def-template :ref
  :db/valueType :db.type/ref}

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

 {:meta/def-template :string-id
  :meta/templates [:string :attr-one :id]}

  ;; Sessions

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

  {:meta/templates [:string-id]
   :db/ident :session/id
   :db/doc "A session's ID."
   :db/noHistory true}

  {:meta/templates [:attr-one :ref]
   :db/ident :session/user
   :db/doc "Which user the session is associated with, if any."
   :db/noHistory true}

  {:meta/templates [:attr-one :string]
   :db/ident :session/metadata
   :db/doc "Any additional information needed on the session."
   :db/noHistory true}

]