vue elementUI select下拉框如何设置默认值

<el-select v-model="valuetype"  @change="changetype">
    <el-option v-for="item in options" :key="item.value" :label="item.label" :value="item.value">
    </el-option>
</el-select>

export default {
        data() {
            return {
                options: [
                    {
                        value: 'all',
                        label: '全部'
                    },
                    {
                        value: 'model',
                        label: '型号'
                    },
                    {
                        value: 'machine',
                        label: '机器'
                    }
                ],
                valuetype: 'all',
            };
        },
     }

<div class="add_item active">
            <div class="add_name"> 参与者：</div>
            <div class="add_input">
              <el-select v-model="edituser_ids" multiple  filterable placeholder="请选择">
                <el-option v-for="item in addOptions" :key="item.value" :label="item.label" :value="item.value">
                </el-option>
              </el-select>
            </div>
          </div>

this.editmain_user_ids = res.data.data.main_user_ids.split(',').map(Number);