//定义一个select下拉菜单
<el-form-item label="类型">
 <el-select v-model="form.typeChanges">
  <el-option label="表结构变更" value="tableChange"></el-option>
  <el-option label="接口变更" value="interfaceChange"></el-option>
  <el-option label="软件升级" value="softChange"></el-option>
  <el-option label="其他" value="otherChange"></el-option>
 </el-select>
</el-form-item>
//通过结合vue-for循环以及vue-id判断条件
//判断条件一：当下拉选中【表结构变更】，即显示以下界面
 <div v-for="item in items" v-if="form.typeChanges=='tableChange'" >
  <div prop="items">
  <el-form-item label="表名：" >
   <el-input v-model="form.tableName" class="col-sm-8"></el-input>
  </el-form-item>
   <el-form-item label="建表SQL：">
   <el-input type="textarea" v-model="form.createSql" class="col-sm-8"></el-input>
   </el-form-item>
  </div>
 </div>
//判断条件二：当下拉选中【接口变更】，即显示以下界面
 <div v-for="item in items" v-if="form.typeChanges=='interfaceChange'">
  <div prop="items">
   <el-form-item label="接口名：">
    <el-input v-model="form.interfaceName" class="col-sm-8"></el-input>
   </el-form-item>
  </div>
 </div>

 <el-form-item label="类型:">
  <el-select class="col-sm-3" v-model="change.types">
   <el-option v-for="option in typeOption" :key="option.value" :label="option.label"
      :value="option.value">
   </el-option>
  </el-select>

  <el-select class="col-sm-6" v-model="change.typeChanges" @change="chooseChild">
   <el-option v-for="option in childtypeOption" :key="option.value" :label="option.label"
      :value="option.value">
   </el-option>
  </el-select>
 </el-form-item>

<script>
 export default {
  name: "change",
  data() {
 change{
 //定义自变量
 types;'',
 typeChanges:'',
 },
 //存放拉下选项，一个选项赋予一个value;
 typeOption: [{label: '申请类', value: '0'}],
   childtypeOption: [{label: '表结构变更', value: '0'}, {label: '接口变更', value: '1'}, 
   {label: '软件升级',value: '2'},{label: '其他',value: '2'},] 
}

</script>

<div id="app">
 <p v-if="seen">现在你看到我了</p>
 <template v-if="ok">
  <h1>v-if教程</h1>
  <p>学的不仅是技术，更是梦想！</p>
  <p>哈哈哈，打字辛苦啊！！！</p>
 </template>
</div>
 
<script>
new Vue({
 el: '#app',
 data: {
 seen: true,
 ok: true
 }
})
</script>

<div id="app">
 <ol>
 <li v-for="site in sites">
  {{ site.name }}
 </li>
 </ol>
</div>
 
<script>
new Vue({
 el: '#app',
 data: {
 sites: [
  { name: 'Runoob' },
  { name: 'Google' },
  { name: 'Taobao' }
 ]
 }
})
</script>