element 表單驗證 el-form-item里面驗證兩個select 必填，select 值綁定為對象時如何驗證必填

el-form-item  里面有多個select 或者input :
　　

<el-form-item label="選項一：" required>
                        <div class="diasubject">
                            <el-form-item prop="stage.code" :rules="[{ required: true, message: '請選擇', trigger: 'change' }]">
                                <el-select v-model="Newtextbooks.cinfigForm.stage" placeholder="請選擇" value-key="code">
                                    <el-option v-for="item in diaFormQArr.stageArr" :key="item.code" :label="item.name" :value="item">
                                    </el-option>
                                </el-select>
                            </el-form-item>
                            <el-form-item prop="subject.code" :rules="[{ required: true, message: '請選擇', trigger: 'change' }]">
                                <el-select v-model="Newtextbooks.cinfigForm.subject" placeholder="請選擇" value-key="code" disabled>
                                    <el-option v-for="item in diaFormQArr.subjectArr" :key="item.code" :label="item.name" :value="item">
                                    </el-option>
                                </el-select>
                            </el-form-item>
                        </div>
                    </el-form-item>

當select 選中值綁定為對象時，el-form-item 上面的prop 只需要 監聽 select 的 v-model 綁定的 stage對象里面某個屬性是否有值，這樣就可以驗證必填