Question

我目前正在跟随om-next tutorial。在Adding Reads部分中，定义了一个函数get-people。除此功能外，还定义了init-data地图，其中包含人员列表。

(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}]})

我尝试调用此功能。

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

如您所见，我只是回到nil s的向量。我不太明白应该怎么称呼这个功能。有人可以帮帮我吗？谢谢！

Answer 1

好吧，我明白了。

init-data不是调用get-people的正确数据结构。首先必须使用Om reconciler“协调”初始数据。您可以在教程的Normalization部分找到有关协调程序的更多信息。

协调init-data地图然后deref数据会返回此规范化数据结构：

{: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}}}

以下是使用已协调的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}]

以下是发生的事情：

首先，该函数检索与:list/one键关联的值。在这种情况下，该值是映射到映射的路径的向量（每个路径本身就是一个向量）。
接下来，映射路径并在每个向量上调用匿名函数。其中一个调用看起来像(get-in st [:person/by-name "John"])并返回{:name "John", :points 0}。
将结果作为向量返回

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Om Next教程：正确调用get-people功能

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