| 在前端开发中，级联选择框是经常用到的，这样不仅可以增加用户输入的友好性，还能减少前后端交互的数据量。本文以elementUI为例，使用其余UI组件大致思想也都相同。
1.数据库设计 所有的相关数据皆可存在一张表中，这样数据就可以不受层级的限制。 表结构可以参考如下建表SQL： CREATE TABLE `supplies_type` ( `id` int(11) NOT NULL AUTO_INCREMENT, `category_type` varchar(64) NOT NULL COMMENT '类别种类：大类、中类、小类', `big_category_name` varchar(64) NOT NULL COMMENT '大类名称', `middle_category_name` varchar(64) DEFAULT NULL COMMENT '中类名称', `small_category_name` varchar(64) DEFAULT NULL COMMENT '小类名称', `parent_id` int(11) DEFAULT NULL, `create_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP, `create_user_name` varchar(64) DEFAULT NULL COMMENT '创建人用户名', `update_time` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP, `is_deleted` tinyint(1) DEFAULT '0' COMMENT '是否删除，1表示已删除', PRIMARY KEY (`id`)) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4; 数据库截图如下图所示，注：本系统为了减少查询次数，故冗余了一些字段，读者可根据自己的需求调整。 
核心设计在于parent_id，根据parent_id字段即可查询到子类，结果如下图所示： 
2.前端页面 前端页面效果如下： 
Html代码如下： <div class="app-container"> <span style="margin-left:120px;margin-right: 20px;width: 150px;display: inline-block;">大类：</span> <el-select v-model="big" placeholder="请选择" @change="getSuppliesType(big)" style="width: 19%;"> <el-option v-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;">中类：</span> <el-select v-model="middle" placeholder="请选择" @change="getSuppliesType(middle)" style="width: 19%;"> <el-option v-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;">小类：</span> <el-select v-model="small" placeholder="请选择" style="width: 19%;"> <el-option v-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数据为后端从数据库中查询出来的数据（驼峰命名），后端只负责查询、并返回结果。 Vue中数据定义如下： data() { return { big: '', bigTypes: null, middle: '', middleTypes: null, small: '', smallTypes: null }},在页面初始化时，自动获取大类列表： created() { this.getSuppliesType(0)},页面中的getSuppliesType方法如下： getSuppliesType(id) { this.listLoading = true const queryData = { parentId: id } //此处的调用后端接口按照自己的调用方式写即可 //此处的getSuppliersType是项目中自己封装的util中的方法 //如果请求方式是post，JSON.stringify(queryData) //如果请求方式是get，queryData getSuppliersType(JSON.stringify(queryData)).then(response => { console.log(response) console.log(response.data[0].categoryType) //根据type自动向三个下拉框赋值 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 })},
3.一个完整的demo 下面这个页面为完成代码，其中的数据为部分数据，后台接口获取使用JS来完成。 <template> <div class="app-container"> <span style="margin-left:120px;margin-right: 20px;width: 150px;display: inline-block;">大类：</span> <el-select v-model="big" placeholder="请选择" @change="getSuppliesType(big)" style="width: 19%;"> <el-option v-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;">中类：</span> <el-select v-model="middle" placeholder="请选择" @change="getSuppliesType(middle)" style="width: 19%;"> <el-option v-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;">小类：</span> <el-select v-model="small" placeholder="请选择" style="width: 19%;"> <el-option v-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 style="margin-left:280px" @click.native.prevent="commit">添加</el-button> <el-button type="primary" round style="margin-left:100px" @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.现场管理与保障","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.生命救援与生活救助","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.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":null,"parentId":1,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":10,"categoryType":"MIDDLE","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.2现场安全","smallCategoryName":null,"parentId":1,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":3,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.1气象监测","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":4,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.2地震监测","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":5,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.3地质灾害监测","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":6,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.4水文监测","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":7,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.5环境监测","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":8,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.6疫病监测","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":9,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.1现场监测","smallCategoryName":"1.1.7观察测量","parentId":2,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":11,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.2现场安全","smallCategoryName":"1.2.1现场照明","parentId":10,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":12,"categoryType":"SMALL","bigCategoryName":"1.现场管理与保障","middleCategoryName":"1.2现场安全","smallCategoryName":"1.2.2现场警戒","parentId":10,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":28,"categoryType":"MIDDLE","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.1人员安全防护","smallCategoryName":null,"parentId":27,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":34,"categoryType":"MIDDLE","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.2生命搜救与营救","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.生命救援与生活救助","middleCategoryName":"2.1人员安全防护","smallCategoryName":"2.1.1卫生防疫","parentId":28,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":30,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.1人员安全防护","smallCategoryName":"2.1.2消防防护","parentId":28,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":31,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.1人员安全防护","smallCategoryName":"2.1.3化学与放射","parentId":28,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":32,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.1人员安全防护","smallCategoryName":"2.1.4防高空坠落","parentId":28,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":33,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.1人员安全防护","smallCategoryName":"2.1.5通用防护","parentId":28,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":35,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.2生命搜救与营救","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.生命救援与生活救助","middleCategoryName":"2.2生命搜救与营救","smallCategoryName":"2.2.2攀岩营救","parentId":34,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":37,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.2生命搜救与营救","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.生命救援与生活救助","middleCategoryName":"2.2生命搜救与营救","smallCategoryName":"2.2.4水下营救","parentId":34,"createTime":"2021-07-04T11:13:36.000+0000","createUserName":null,"updateTime":null,"isDeleted":false}, {"id":39,"categoryType":"SMALL","bigCategoryName":"2.生命救援与生活救助","middleCategoryName":"2.2生命搜救与营救","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 } //此处为js模拟，真实数据的获取还需要后台接口的支持 getSuppliersType(JSON.stringify(queryData)).then(response => { console.log(response) console.log(response.data[0].categoryType) //存放此次查询结果 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("点击了提交按钮") }, cancel() { this.$router.go(-1) } } }</script> 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