1. 实现效果：

2.后端返回的数据格式

只有一个list，多数文章中都是两个list实现联动

"list": [
      {
        "id": "1178214681118568449",
        "title": "后端开发",
        "children": [
          {
            "id": "1178214681139539969",
            "title": "Java"
          },
          {
            "id": "1178585108407984130",
            "title": "Python"
          },
          {
            "id": "1454645056483913730",
            "title": "C++"
          },
          {
            "id": "1454645056731377666",
            "title": "C#"
          }
        ]
      },
      {
        "id": "1178214681181483010",
        "title": "前端开发",
        "children": [
          {
            "id": "1178214681210843137",
            "title": "JavaScript"
          },
          {
            "id": "1178585108454121473",
            "title": "HTML/CSS"
          }
        ]
      },
      {
        "id": "1178214681231814658",
        "title": "云计算",
        "children": [
          {
            "id": "1178214681252786178",
            "title": "Docker"
          },
          {
            "id": "1178214681294729217",
            "title": "Linux"
          }
        ]
      },
      {
        "id": "1178214681324089345",
        "title": "系统/运维",
        "children": [
          {
            "id": "1178214681353449473",
            "title": "Linux"
          },
          {
            "id": "1178214681382809602",
            "title": "Windows"
          }
        ]
      },
      {
        "id": "1178214681399586817",
        "title": "数据库",
        "children": [
          {
            "id": "1178214681428946945",
            "title": "MySQL"
          },
          {
            "id": "1178214681454112770",
            "title": "MongoDB"
          }
        ]
      },
      {
        "id": "1178214681483472898",
        "title": "大数据",
        "children": [
          {
            "id": "1178214681504444418",
            "title": "Hadoop"
          },
          {
            "id": "1178214681529610242",
            "title": "Spark"
          }
        ]
      },
      {
        "id": "1178214681554776066",
        "title": "人工智能",
        "children": [
          {
            "id": "1178214681584136193",
            "title": "Python"
          }
        ]
      },
      {
        "id": "1178214681613496321",
        "title": "编程语言",
        "children": [
          {
            "id": "1178214681626079234",
            "title": "Java"
          }
        ]
      }
    ]

 3、vue页面中代码

 <!-- 所属分类 TODO -->
      <el-form-item label="课程分类">
        <!--一级分类-->
        <el-select
          v-model="courseInfo.subjectParentId"
          placeholder="一级分类" @change="subjectLevelOneChanged">
          <el-option
            v-for="subject in subjectOneList"
            :key="subject.id"
            :label="subject.title"
            :value="subject.id"/>
        </el-select>

        <!-- 二级分类 -->
        <el-select v-model="courseInfo.subjectId" placeholder="请选择">
          <el-option
            v-for="subject in subjectTwoList"
            :key="subject.value"
            :label="subject.title"
            :value="subject.id"/>
        </el-select>
      </el-form-item>

import course from '@/api/edu/course'
import subject from '@/api/edu/subject'
export default {
  data() {
    return {
      saveBtnDisabled: false, // 保存按钮是否禁用
      courseInfo:{
        title: '',
        subjectId: '',      //二级分类id
        subjectParentId:'', //一级分类id
        teacherId: '',      //讲师id
        lessonNum: 0,       //课时
        description: '',    //课程简介
        cover: '/static/01.jpg',          //默认封面图片
        price: 0
      },
      teacherList:[],  //封装所有的讲师数据
      subjectOneList:[],  //一级分类
      subjectTwoList:[] ,  //二级分类
      BASE_API: process.env.BASE_API // 接口API地址
    }
  },
  created() { //页面渲染之前执行
    //初始化所有讲师
    this.getListTeacher()
    //初始化一级分类
    this.getOneSubject()
  },
  methods: {
    //点击某个一级分类，会触发change事件，显示对应的二级分类
    subjectLevelOneChanged(value){
        //value就是一级分类的id值
        //先遍历所有的分类 里面包含一级和二级
      for (var i = 0; i <this.subjectOneList.length; i++) {
        //每个一级分类
        var oneSubject=this.subjectOneList[i]
        //判断：所有一级分类id和点击一级分类id是否一样
        //如果没有id，使用数组内其他属性对比也可以，比如name等
        if(value===oneSubject.id){  //===即比较值 还要比较类型
          //从一级分类中获取所有的二级分类
          this.subjectTwoList=oneSubject.children
          //把二级分类Id值清空
          this.courseInfo.subjectId=''
        }
      }
    },
    //查询所有的一级分类
    getOneSubject(){
      subject.getSubjectList()
      .then(response=>{
        this.subjectOneList=response.data.list
      })
    }
  }
}
</script>

 文章转载：vue实现下拉框二级联动效果-腾讯云开发者社区-腾讯云

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