我正在关注《专业Clojure》一书的第6章。
应用状态目前定义如下:
(defonce app-state
(reagent/atom
{:projects
{"aaa"
{:title "Build Whip"
:stories
{1 {:title "Design a data model for projects and stories"
:status "done"
:order 1}
2 {:title "Create a story title entry form"
:order 2}
3 {:title "Implement a way to finish stories"
:order 3}}}}}))
我需要使用swap!
一个新的键值来表示一个新的故事,该键值由具有给定字段值的id来键控。
(defn add-story! [app-state project-id title status] ;
; Q. How to use swap! to add a key value pair into :stories?
(swap! app-state update [:projects project-id :stories] assoc <- INCORRECT CODE HERE
(unique) {:title title
:status status
:order (inc (max-order app-state project-id))}))
此处未显示的唯一函数只会生成任何唯一的uuid。最大阶函数可以得到最大阶。由于书中的章节与实际提供的最终代码不一致,因此我不得不对其进行修改。这是我的max-order版本:
(defn max-order [app-state project-id]
(apply max 0 (map :order (vals (get-in @app-state [:projects project-id :stories])))))
问题:如何使用swap!
新的键值添加到:stories
?
我尝试了一下,但现在它击败了我。
我确实感觉到此嵌套 map不是最好的表示法-在作为下载提供的最终代码中,作者已更改为关系类型更多的模型,其中项目和故事都是顶级实体,故事包含project_id,但是swap!
在继续之前先解决它的第一次使用将是一个不错的选择。
我认为您可以assoc-in
在这种情况下使用它,它比简单一些,update-in
并且可以更好地描述您要实现的目标:
(def app-state
(atom
{:projects
{"aaa"
{:title "Build Whip"
:stories {1 {:title "Design a data model for projects and stories"
:status "done"
:order 1}
2 {:title "Create a story title entry form"
:order 2}
3 {:title "Implement a way to finish stories"
:order 3}}}}}))
(defn unique [] (rand-int 1000000000))
(let [unique-key (unique)]
(swap! app-state
assoc-in
[:projects "aaa" :stories unique-key]
{:title (str "Agent " unique-key)
:status "foxy"
:order "some-order-stuff"}))
@app-state
;; => {:projects
;; {"aaa"
;; {:title "Build Whip",
;; :stories
;; {1 {:title "Design a data model for projects and stories", :status "done", :order 1},
;; 2 {:title "Create a story title entry form", :order 2},
;; 3 {:title "Implement a way to finish stories", :order 3},
;; 295226401 {:title "Agent 295226401", :status "foxy", :order "some-order-stuff"}}}}}