小编gra*_*ton的帖子

我正在尝试通过REST API在Datomic中进行"外连接".来自https://github.com/Datomic/day-of-datomic/blob/master/tutorial/social_news.clj我已经采取了最后的例子:

(defn maybe
  "Returns the set of attr for e, or nil if e does not possess
   any values for attr."
  [db e attr]
  (seq (map :a (d/datoms db :eavt e attr))))

;; find all users 
(q '[:find ?e ?upvote
     :where
     [?e :user/email]
     [(user/maybe $ ?e :user/upVotes) ?upvote]]
   (db conn))

我将maybe函数插入到我的数据库中,因此可以查询:

[:find ?n ?v :in $ :where [?e ?a ?v] [?a :db/ident :db/fn] [?e :db/ident ?n]]

回报

:maybe  #db/fn{:code "(seq (map :a (d/datoms db :eavt e attr)))", …