element 表单验证 el-form-item里面验证两个select 必填，select 值绑定为对象时如何验证必填

el-form-item  里面有多个select 或者input :

<el-form-item label="学段学科：" required>
                        <div class="diasubject">
                            <el-form-item prop="stage" :rules="[{ required: true, message: '请选择学段', trigger: 'change' }]">
                                <el-select v-model="Newtextbooks.cinfigForm.stage" placeholder="请选择学段">
                                    <el-option v-for="item in diaFormQArr.stageArr" :key="item.code" :label="item.name" :value="item.code">
                                    </el-option>
                                </el-select>
                            </el-form-item>
                            <el-form-item prop="subject" :rules="[{ required: true, message: '请选择学科', trigger: 'change' }]">
                                <el-select v-model="Newtextbooks.cinfigForm.subject" placeholder="请选择学科">
                                    <el-option v-for="item in diaFormQArr.subjectArr" :key="item.code" :label="item.name" :value="item.code">
                                    </el-option>
                                </el-select>
                            </el-form-item>
                        </div>
                    </el-form-item>

 

当select 选中值绑定为对象时，el-form-item 上面的prop 只需要 监听 select 的 v-model 绑定的 stage对象里面某个属性是否有值，这样就可以验证必填