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今天來講個有關二進位的實務運用(人員權限控管)，也是筆者第一個接手的案子用到的技術
CRUD 這幾個字相信大家都不陌生吧，如果不認識的話那改為中文的「增刪查改」
是電腦中常見的四個動作(更為詳細的還請參照維基 )
那我們這次就以這四個動作針對人員權限控管來舉例
可以看到位數從右到左分別就是CRUD、跟二進位的位數
二進位換算成十進位的方式，這裡就不特別解釋了，詳情可參考維基
那開始正式進入範例
範例說明 #1. 權限控管-設定 小明
那我們該怎麼表示呢
對應第一章圖的總表，大家應該可以輕鬆得出這個答案吧 (二進位表示 0011、十進位數字則為 3 )
至於U跟D則是他沒有的權限所以均為 0
#2. 權限控管-判斷 某天，神秘黑衣人找上小明
於是小明
判斷是否有權限是要用AND
而二進位的計算在SQL中是可以直接這樣子表示，各語言也均有類似的
計算出來的答案為 0 ，故沒有成立(成功有權限的話，結果應該要為 0100 = 22 = 4 )
自然改不了黑衣人的資料
#3. 權限控管- 增加沒辦法達成黑衣人需求，小明
再經過一番死纏爛打之後，網管最終還是同意了幫他新增「U修改」及「D刪除」的權限
要新增權限的話，要用到二進位中的OR
#4. 權限控管- 減少擁有所有權限的小明
不料終究紙包不住火，在內部財務稽核的時候還是東窗事發了…
老闆念在小明
這裡用到的是二進位的XOR
可以看到在經過處理之後，小明 1 = 2)
優點及其限制 想到判斷權限，第一個會想到的架構應該會是，一個權限對應一個欄位吧
舉例如下，假設有多個功能要做限制 (Y/N表示有無此權限)
資料庫範例 看起來確實不錯，但要是功能一多就必須要開同等數目的欄位，是不是有一點麻煩
那如果用剛剛講到的二進位來表示呢
看起來是不是簡單了很多!
優點 限制 **受限於數據類型 資料不直觀，需透過權限二進位字典對應 (像是範例最前面的圖1，告知各權限與二進位關聯，可能用DB另一張Table來儲存)
這裡講解一下受限於數據類型 的意思，舉例來說Auth 權限欄位設定為Integer
Integer最大值為 232 -1，故最多只能儲存32個權限
結論 這裡來整理下上面所說的動作及二進位計算的關聯表
針對二進位權限動作的計算方式
這次講解完二進位的權限控管，但其實還是要根據不同的情境來考慮使用
像是若是頁面僅有兩、三個權限，且不會經常更改，那直接用欄位儲存不用二進位計算，可能在效能上反而更好
"Human beings rarely do things for a binary reason"
Laura Kuenssberg
封面照片 : Photo by Danielle Rice on Unsplash
最新資訊文章
有趣程式分享 二進位(binary) , 圖文介紹 , 權限控管 Continue Reading
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