vue+element下拉列表默认值问题

 deviceSNMPList: [
          {
            key: '0',
            label: 'v1'
          },
          {
            key: '1',
            label: 'v2c'
          },
          {
            key: '3',
            label: 'v3'
          }
        ],
        deviceSNMP:'1',

 <el-form :model="form" inline="true" ref="form" style="margin-bottom: -20px;margin-top:-20px">
	 <el-form-item style="margin-bottom: -10px; width: 100%" label="*SNMP版本:" :label-width="formLabelWidth"
                      prop="string">
          <el-select clearable size='mini' v-model="deviceSNMP" placeholder="请选择活动区域" autocomplete="off"
                     style="width: 100%">
            <el-option v-for="item in deviceSNMPList" :key="item.key" :label="item.label"
                       :value="item.key"></el-option>
          </el-select>
        </el-form-item>
 <el-form>

<el-select
       v-model="xialaValue"
       placeholder="请输入关联公式"
 >
    <el-option
      v-for="item in roleOptions"
      :key="item.value"
      :label="item.label"
      :value="item.value"
    ></el-option>
</el-select>

data() {
    return {
        roleOptions:[
            {
                value:'1',
                label:'选项一'
            },
            {
                value:'2',
                label:'选项二'
            },
            {
                value:'3',
                label:'选项三'
            },
    ]
  }
}

this.xialaValue='1'