​ 在前端開發中，級聯選擇框是經常用到的，這樣不僅可以增加用戶輸入的友好性，還能減少前后端交互的數據量。本文以elementUI為例，使用其余UI組件大致思想也都相同。

​ 所有的相關數據皆可存在一張表中，這樣數據就可以不受層級的限制。

​ 表結構可以參考如下建表SQL：

CREATE TABLE `supplies_type` ( `id` int(11) NOT NULL AUTO_INCREMENT, `category_type` varchar(64) NOT NULL COMMENT ’類別種類：大類、中類、小類’, `big_category_name` varchar(64) NOT NULL COMMENT ’大類名稱’, `middle_category_name` varchar(64) DEFAULT NULL COMMENT ’中類名稱’, `small_category_name` varchar(64) DEFAULT NULL COMMENT ’小類名稱’, `parent_id` int(11) DEFAULT NULL, `create_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP, `create_user_name` varchar(64) DEFAULT NULL COMMENT ’創建人用戶名’, `update_time` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP, `is_deleted` tinyint(1) DEFAULT ’0’ COMMENT ’是否刪除，1表示已刪除’, PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4;

數據庫截圖如下圖所示，注：本系統為了減少查詢次數，故冗余了一些字段，讀者可根據自己的需求調整。

核心設計在于parent_id，根據parent_id字段即可查詢到子類，結果如下圖所示：

​ 前端頁面效果如下：

Html代碼如下：

<div class='app-container'> <span style='margin-left:120px;margin-right: 20px;width: 150px;display: inline-block;'>大類：</span> <el-select v-model='big' placeholder='請選擇' @change='getSuppliesType(big)' style='width: 19%;'> <el-optionv-for='item in bigTypes':key='item.bigCategoryName':label='item.bigCategoryName':value='item.id'> </el-option> </el-select> <span style='margin-left:120px;margin-right: 20px; width: 150px;display: inline-block;'>中類：</span> <el-select v-model='middle' placeholder='請選擇' @change='getSuppliesType(middle)' style='width: 19%;'> <el-optionv-for='item in middleTypes':key='item.middleCategoryName':label='item.middleCategoryName':value='item.id'> </el-option> </el-select> <br> <br> <br> <span style='margin-left:120px;margin-right: 20px;width: 150px; margin-top:20px; display: inline-block;'>小類：</span> <el-select v-model='small' placeholder='請選擇' style='width: 19%;'> <el-optionv-for='item in smallTypes':key='item.smallCategoryName':label='item.smallCategoryName':value='item.id'> </el-option> </el-select></div>

​ 上面的item.smallCategoryName、item.smallCategoryName數據為后端從數據庫中查詢出來的數據（駝峰命名），后端只負責查詢、并返回結果。

Vue中數據定義如下：

data() { return {big: ’’,bigTypes: null,middle: ’’,middleTypes: null,small: ’’,smallTypes: null }},

在頁面初始化時，自動獲取大類列表：

created() {this.getSuppliesType(0)},

頁面中的getSuppliesType方法如下：

getSuppliesType(id) { this.listLoading = true const queryData = { parentId: id } //此處的調用后端接口按照自己的調用方式寫即可 //此處的getSuppliersType是項目中自己封裝的util中的方法 //如果請求方式是post，JSON.stringify(queryData) //如果請求方式是get，queryData getSuppliersType(JSON.stringify(queryData)).then(response => { console.log(response) console.log(response.data[0].categoryType) //根據type自動向三個下拉框賦值 if (response.data[0].categoryType === ’BIG’) { this.bigTypes = response.data } else if (response.data[0].categoryType === ’MIDDLE’) { this.middleTypes = response.data } else { this.smallTypes = response.data } this.listLoading = false }).catch(function (error) { console.log(error) this.listLoading = false })},3.一個完整的demo

​ 下面這個頁面為完成代碼，其中的數據為部分數據，后臺接口獲取使用JS來完成。

<template> <div class='app-container'> <span style='margin-left:120px;margin-right: 20px;width: 150px;display: inline-block;'>大類：</span> <el-select v-model='big' placeholder='請選擇' @change='getSuppliesType(big)' style='width: 19%;'> <el-optionv-for='item in bigTypes':key='item.bigCategoryName':label='item.bigCategoryName':value='item.id'> </el-option> </el-select> <span style='margin-left:120px;margin-right: 20px; width: 150px;display: inline-block;'>中類：</span> <el-select v-model='middle' placeholder='請選擇' @change='getSuppliesType(middle)' style='width: 19%;'> <el-optionv-for='item in middleTypes':key='item.middleCategoryName':label='item.middleCategoryName':value='item.id'> </el-option> </el-select> <br> <br> <br> <span style='margin-left:120px;margin-right: 20px;width: 150px; margin-top:20px; display: inline-block;'>小類：</span> <el-select v-model='small' placeholder='請選擇' style='width: 19%;'> <el-optionv-for='item in smallTypes':key='item.smallCategoryName':label='item.smallCategoryName':value='item.id'> </el-option> </el-select> <br> <br> <br> <el-button type='primary' round @click.native.prevent='commit'>添加</el-button> <el-button type='primary' round @click.native.prevent='cancel'>取消</el-button> </div></template><script> export default {filters: { parseTime(timestamp) {return parseTime(timestamp, null) }},data() { return {big: ’’,bigTypes: null,middle: ’’,middleTypes: null,small: ’’,smallTypes: null,dataList: [ {'id':1,'categoryType':'BIG','bigCategoryName':'1.現場管理與保障','middleCategoryName':null,'smallCategoryName':null,'parentId':0,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':'2021-07-04T13:34:31.000+0000','isDeleted':false}, {'id':27,'categoryType':'BIG','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':null,'smallCategoryName':null,'parentId':0,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':2,'categoryType':'MIDDLE','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':null,'parentId':1,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':10,'categoryType':'MIDDLE','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.2現場安全','smallCategoryName':null,'parentId':1,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':3,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.1氣象監測','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':4,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.2地震監測','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':5,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.3地質災害監測','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':6,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.4水文監測','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':7,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.5環境監測','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':8,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.6疫病監測','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':9,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.1現場監測','smallCategoryName':'1.1.7觀察測量','parentId':2,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':11,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.2現場安全','smallCategoryName':'1.2.1現場照明','parentId':10,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':12,'categoryType':'SMALL','bigCategoryName':'1.現場管理與保障','middleCategoryName':'1.2現場安全','smallCategoryName':'1.2.2現場警戒','parentId':10,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':28,'categoryType':'MIDDLE','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.1人員安全防護','smallCategoryName':null,'parentId':27,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':34,'categoryType':'MIDDLE','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.2生命搜救與營救','smallCategoryName':null,'parentId':27,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':'2021-07-04T13:03:23.000+0000','isDeleted':false}, {'id':29,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.1人員安全防護','smallCategoryName':'2.1.1衛生防疫','parentId':28,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':30,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.1人員安全防護','smallCategoryName':'2.1.2消防防護','parentId':28,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':31,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.1人員安全防護','smallCategoryName':'2.1.3化學與放射','parentId':28,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':32,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.1人員安全防護','smallCategoryName':'2.1.4防高空墜落','parentId':28,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':33,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.1人員安全防護','smallCategoryName':'2.1.5通用防護','parentId':28,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':35,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.2生命搜救與營救','smallCategoryName':'2.2.1生命搜索','parentId':34,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':36,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.2生命搜救與營救','smallCategoryName':'2.2.2攀巖營救','parentId':34,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':37,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.2生命搜救與營救','smallCategoryName':'2.2.3破拆起重','parentId':34,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':38,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.2生命搜救與營救','smallCategoryName':'2.2.4水下營救','parentId':34,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false}, {'id':39,'categoryType':'SMALL','bigCategoryName':'2.生命救援與生活救助','middleCategoryName':'2.2生命搜救與營救','smallCategoryName':'2.2.5通用工具','parentId':34,'createTime':'2021-07-04T11:13:36.000+0000','createUserName':null,'updateTime':null,'isDeleted':false} ] }},created() { this.getSuppliesType(0)},methods: { getSuppliesType(id) {const queryData = { parentId: id}//此處為js模擬，真實數據的獲取還需要后臺接口的支持getSuppliersType(JSON.stringify(queryData)).then(response => { console.log(response) console.log(response.data[0].categoryType) //存放此次查詢結果 let tmpList = [] this.dataList.forEach((item, index) => {if(item.parentId === id){ tmpList.push(item)} }) if (tmpList[0].categoryType === ’BIG’) {this.bigTypes = tmpList } else if (response.data[0].categoryType === ’MIDDLE’) {this.middleTypes = tmpList } else {this.smallTypes = tmpList }}).catch(function (error) { console.log(error)}) }, commit() {console.log('點擊了提交按鈕') }, cancel() {this.$router.go(-1) }} }</script>

​ 又到了分隔線以下，本文到此就結束了，本文內容全部都是由博主自己進行整理并結合自身的理解進行總結

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