datomic registry

datomic_registry.clj

(ns components.datomic-registry.service
  (:require [datomic.api :as d]
            [components.lifecycle.protocol :as lifecycle]
            [components.datomic.service :refer [make-uri]]
            [components.datomic-registry.protocol :as protocol]))

(defrecord DatomicRegistryService [db ns-name state]
  lifecycle/Lifecycle
  (start [this system]
    (let [db (lifecycle/handler db)
          id-field (keyword (name ns-name) "id")
          dbs (->> (d/q [:find '?c :in '$ :where
                         ['?c id-field]]
                        (d/db db))
                   (map first)
                   (map (partial d/entity (d/db db)))
                   ;; remove namespace from attribute names
                   (map #(reduce-kv (fn [m k v]
                                      (assoc m (keyword (name k)) v)) {} %))
                   ; index by id
                   (map (juxt :id identity))
                   (into {}))]
      (swap! state assoc :registry dbs)))

  (stop [this system]
    (doseq [conn  (keep (comp :datomic second) (:registry @state))]
      (d/release conn)))

  lifecycle/Service
  (handler [this]
    this) ; to avoid any confusion

  protocol/Registry
  (get-db [this db-id]
    (let [m (swap! state
                   (fn [current-state]
                     (if-let [db-reg (get-in current-state [:registry db-id])]
                       (if (nil? (:datomic db-reg))
                         (assoc-in current-state
                                   [:registry db-id :datomic]
                                   (d/connect (make-uri (:driver db-reg)
                                                        db-reg)))
                         ;; already connected
                         current-state)
                       ;; unknown database
                       current-state)))]
      (get m [:registry db-id :datomic]))))

(defn make [db ns-name]
  "Creates a service instance. Entities should have the follwing attributes:
   - :<ns-name>/driver (one of #{:postgres :sql-server :cassandra :mem})
   - :<ns-name>/id (keyword)
   - :<ns-name>/db (string)
   - :<ns-name>/host (string)
   - :<ns-name>/port (long)
   - :<ns-name>/user (string)
   - :<ns-name>/password (string)"
  (->DatomicRegistryService db ns-name (atom {})))