Om Next教程:正确调用get-people功能

Question

我目前正在按照om-next 教程进行操作.在" 添加读取"部分中,get-people定义了一个函数.除此功能外,init-data还定义了包含人员列表的地图.

(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}]})

这是我尝试调用此函数.

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

如你所见,我只是回到了nils 的向量.我不太明白我该如何调用这个函数.有人可以帮帮我吗？谢谢!

Answer 1

好吧,我明白了.

init-data不是要调用的正确数据结构get-people.首先必须使用Om's"协调"初始数据reconciler.您可以在教程的" 规范化"部分中找到有关协调程序的更多信息.

协调init-data地图然后deref输入数据将返回此规范化的数据结构:

{: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get-people使用已协调的init-data 对函数的有效调用:

; 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}]

这是发生了什么:

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

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