element-ui select多选绑定回显值问题

 <el-form-item label="机组名称" prop="unitName">
	<el-select
	     v-model="unitName"
	     multiple
	     placeholder="请选择"
	    @change="unitChange"
	>
	   <el-option
	       v-for="item in jzmcOption"
	       :key="item.unitId"
	       :label="item.unitName"
	       :value="item.unitId"
	    ></el-option>
	</el-select>
</el-form-item>

unitName:[],
jzmcOption:[],

  unitChange(val) {
      console.log(val);
      let str = val.join(',');
      let name = '';
      this.jzmcOption.map((v, i) => {
        val.map((a, b) => {
          if (a == v.unitId) {
            name += ',' + v.unitName;
          }
        });
      });
      name = name.substring(1);
      this.jydyForm.unitName = name;
      this.jydyForm.unitId = str;
    },
    

    // 查看 编辑
    handleCheckLxr(row, status) {   
      //将id值赋值给下拉框绑定的值
      this.unitName = this.jydyForm.unitId.split(',');      

      let i = this.jydyForm.unitId.split(',');
      let n = this.jydyForm.unitName.split(',');
      let list = [];
      i.map((v, i) => {
        list.push({ unitId: v, unitName: n[i] });
      });
      
      this.jzmcOption = [];
      getChooseByCustomerId(this.currentCustomerId).then(res => {
        
        if (res.rel) {
          let list_o = res.data.rows;
          this.jzmcOption = [...list_o,...list];        
        }
      });
    },

<el-select @change="selectChangeHandle" ...>...</el-select>

selectChangeHandle(){
    this.$forceUpdate()
}