Om下一教程:正确调用get-people函数

Question

我目前正在关注om-next tutorial。在Adding Reads部分中，定义了一个函数get-people。除了此函数之外，还定义了包含人员列表的init-data映射。

(defn get-people [state key]
  (let [st @state]
    (into [] (map #(get-in st %)) (get st key))))

(def init-data {:list/one
 [{:name "John", :points 0}
  {:name "Mary", :points 0}
  {:name "Bob", :points 0}],
 :list/two
 [{:name "Mary", :points 0, :age 27}
  {:name "Gwen", :points 0} 
  {:name "Jeff", :points 0}]})

下面是我调用此函数的尝试。

(get-people (atom init-data) :list/one) ;; => [nil nil nil]

如你所见，我只是返回了一个nil的向量。我不太明白该如何调用这个函数。有人能帮帮我吗？谢谢!

Answer 1

好吧，我想通了。

init-data不是用于调用get-people的正确数据结构。初始数据必须首先使用Om的reconciler进行“协调”。您可以在本教程的Normalization部分找到有关协调器的更多信息。

协调init-data映射，然后对数据执行deref操作，将返回以下标准化数据结构：

{:list/one
 [[:person/by-name "John"]
  [:person/by-name "Mary"]
  [:person/by-name "Bob"]],
 :list/two
 [[:person/by-name "Mary"]
  [:person/by-name "Gwen"]
  [:person/by-name "Jeff"]],
 :person/by-name
 {"John" {:name "John", :points 0},
  "Mary" {:name "Mary", :points 0, :age 27},
  "Bob" {:name "Bob", :points 0},
  "Gwen" {:name "Gwen", :points 0},
  "Jeff" {:name "Jeff", :points 0}}}

下面是使用协调后的init-data对get-people函数的有效调用：

; reconciled initial data
(def reconciled-data
  {:list/one
   [[:person/by-name "John"]
    [:person/by-name "Mary"]
    [:person/by-name "Bob"]],
   :list/two
   [[:person/by-name "Mary"]
    [:person/by-name "Gwen"]
    [:person/by-name "Jeff"]],
   :person/by-name
   {"John" {:name "John", :points 0},
    "Mary" {:name "Mary", :points 0, :age 27},
    "Bob" {:name "Bob", :points 0},
    "Gwen" {:name "Gwen", :points 0},
    "Jeff" {:name "Jeff", :points 0}}}

; correct function call
(get-people (atom reconciled-data) :list/one)

; returned results
[{:name "John", :points 0}
 {:name "Mary", :points 0, :age 27}
 {:name "Bob", :points 0}]

下面是正在发生的事情：

1. 首先，该函数检索与:list/one键关联的值。在本例中，该值是映射的路径向量(每个路径本身都是路径上的vector).
2. Next，映射，并对每个向量调用匿名函数。其中一个调用类似于(get-in st [:person/by-name "John"])，并以向量

的形式返回{:name "John", :points 0}.

• Return结果

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