Some Datomic helpers I sometimes use with ring or pedestal-service apps

datomic-helpers.clj

(ns datomic-helpers
  (:require [datomic.api     :as d]))

;;; Expose Datomic vars here, for convenience

;;; Ring middleware

(defn wrap-datomic
  "A Ring middleware that provides a request-consistent database connection and
  value for the life of a request."
  [handler uri]
  (fn [request]
    (let [conn (d/connect uri)]
      (handler (assoc request
                 :conn conn
                 :db   (d/db conn))))))

;;; Sample handler

(defn create-entity-tx
  "Dummy helper fn."
  [db tempid]
  [[:db/add tempid :db/doc "Some useful work should be done here."]])

(defn create-entity
  "Include :db-after in response map, so that middleware on the way
  \"out\" have updated db value.  Or you could include the entire tx
  result."
  [{:keys [conn db] :as request}]
  (let [tempid (d/tempid :db.part/user)
        result @(d/transact conn (create-entity-tx db tempid))]
    {:status   201
     :body     "Done!"
     :headers  {}
     :db-after (:db-after result)}))

;;; Rules-based predicates

(defn predicate-from-rules
  "Returns a predicate fn that will return true when the predicate-rules (a subset of
  the source-rules) are satisfied, and false otherwise."
  [source-rules predicate-rules]
  (fn [entity]
    (when entity
      (boolean
       (ffirst
        (q (concat '[:find ?e
                     :in $ $id %
                     :where [(= ?e $id)]]
                   predicate-rules)
           (:db/id entity)
           source-rules))))))

;;; Map => Transaction Helpers

;; The functionality that was previously here is now provided by
;; Datomic: i.e. nested maps in transactions.

;;; Query

;; For a better set of query helpers, please see https://github.com/Datomic/day-of-datomic/blob/master/src/datomic/samples/query.clj

;;; Enum => HTML <select> options

(def dropdown-schema
  [{:db/id          (tempid :db.part/db)
    :db/ident       :option/text
    :db/valueType   :db.type/string
    :db/index       true
    :db/cardinality :db.cardinality/one
    :db/doc         "The user-facing text content of an option tag"
    :db.install/_attribute :db.part/db}

   {:db/id          (tempid :db.part/db)
    :db/ident       :option/value
    :db/valueType   :db.type/string
    :db/index       true
    :db/cardinality :db.cardinality/one
    :db/doc         "The user-facing value attribute of an option tag"
    :db.install/_attribute :db.part/db}

   {:db/id          (tempid :db.part/db)
    :db/ident       :option/attribute
    :db/valueType   :db.type/ref
    :db/cardinality :db.cardinality/one
    :db/doc         "The attribute to which this option corresponds"
    :db.install/_attribute :db.part/db}])

(defn option-value->ident
  "Given an attribute and an option value, returns the correpsonding datomic entity ident."
  [attribute value]
  (ffirst
   (q '[:find  ?ident
        :in    $ ?attribute ?value
        :where
        [?e :option/value ?value]
        [?e :option/attribute ?a]
        [?e :db/ident ?ident]
        [?a :db/ident ?attribute]]
      attribute
      value)))

(defn attribute->options
  "Returns all the valid options for the given attribute."
  [attribute]
  (find-all
   '[:find  ?e
     :in    $ ?attr
     :where
     [?e :option/attribute ?a]
     [?a :db/ident ?attr]]
   attribute))