小程序三级联动，实现三级分类，顶部导航栏，左侧分类栏，右侧数据列表

<!-- 导航栏 -->
<scroll-view scroll-x class="navbar" scroll-with-animation scroll-left="{{scrollLeft}}rpx">
  <view class="nav-item" wx:for="{{tabs}}" wx:key="id" bindtap="tabSelect" data-id="{{index}}">
    <view class="nav-text {{index==tabCur?'tab-on':''}}">{{item._id}}</view>
  </view>
</scroll-view>
<view class="container">
  <!-- 左边的  -->
  <scroll-view class='nav_left' scroll-y='true'>
    <block wx:for="{{lefts}}" wx:key="{{index}}">
      <view class="nav_left_items {{leftCur==index?'active':''}}" bindtap="switchLeftTab" data-index='{{index}}'>
        {{item._id}}</view>
    </block>
  </scroll-view>
  <!-- 右边的 -->
  <scroll-view class="nav_right" scroll-y="true">
    <view class="{{topx}}">
      <block wx:for="{{rights}}" wx:key="index">
        <view class="nav_right_items" data-id="{{item._id}}">
          <image src="{{item.touxiang}}"></image>
          <text>{{item.mingzi}}</text>
        </view>
      </block>
    </view>
  </scroll-view>
</view>

/* 导航栏布局相关 */
.navbar {
	width: 100%;
	height: 90rpx;
	/* 文本不换行 */
	white-space: nowrap;
	display: flex;
	box-sizing: border-box;
	border-bottom: 1rpx solid #eee;
	background: #fff;
	align-items: center;
	/* 固定在顶部 */
	position: fixed;
	left: 0rpx;
	top: 0rpx;
}

.nav-item {
	padding-left: 25rpx;
	padding-right: 25rpx;
	height: 100%;
	display: inline-block;
	/* 普通文字大小 */
	font-size: 28rpx;
}

.nav-text {
	width: 100%;
	height: 100%;
	display: flex;
	align-items: center;
	justify-content: center;
	letter-spacing: 4rpx;
	box-sizing: border-box;
}

.tab-on {
	color: #000080;
	/* 选中放大 */
	font-size: 38rpx !important;
	font-weight: 600;
	border-bottom: 4rpx solid #000080 !important;
}

/* 正文部分 */
.container {
	position: fixed;
	width: 100%;
	height: 90%;
	top: 100rpx;
	background-color: #FFF;
}

.nav_left {
	width: 25%;
	height: 100%;
	background: #F2F2F2;
	text-align: center;
	position: absolute;
	top: 0;
	left: 0;
}

.nav_left .nav_left_items {
	height: 100rpx;
	line-height: 100rpx;
	font-size: 28rpx;
}

.nav_left .nav_left_items.active {
	position: relative;
	background: #FFF;
	color: #000080;
}

.nav_left .nav_left_items.active::before {
	display: inline-block;
	width: 6rpx;
	height: 60rpx;
	background: #000080;
	content: '';
	position: absolute;
	top: 20rpx;
	left: 0;
}

.nav_right {
	position: absolute;
	top: 0;
	right: 0;
	width: 75%;
	height: 100%;
}

.nav_right .nav_right_items {
	float: left;
	width: 33.33%;
	text-align: center;
	padding: 30rpx 0;
}

.nav_right .nav_right_items image {
	width: 120rpx;
	height: 160rpx;
}

.nav_right .nav_right_items text {
	display: block;
	margin-top: 20rpx;
	font-size: 28rpx;
	overflow: hidden;
	white-space: nowrap;
	text-overflow: ellipsis;
}

.nocate {
	padding: 100rpx;
	text-align: center;
}

.nocate image {
	width: 70rpx;
	height: 70rpx;
}

.nocate text {
	font-size: 28rpx;
	display: block;
	color: #BBB;
}

/*隐藏滚动条*/
::-webkit-scrollbar {
	width: 0;
	height: 0;
	color: transparent;
}

.topx {
	width: 90%;
	/* height: 700rpx; */
	margin: 30rpx auto;
	z-index: 1;
	border-radius: 10rpx;
	background-size: cover;
}

const db = wx.cloud.database()
const $ = db.command.aggregate
Page({
	data: {
		tabs: [],
		tabCur: 0, //默认选中
		lefts: [],
		leftCur: 0,
		rights: [],

	},
	onLoad: function (options) {
		db.collection('demo').aggregate()
			.group({
				_id: '$louhao'
			})
			.end()
			.then(res => {
				console.log('楼号列表', res)
				this.setData({
					tabs: res.list
				})
				this.sushehao(res.list[0]._id)
			})
	},
	//加载当前楼号所有的宿舍号
	sushehao() {
		let louhao = this.data.tabs[this.data.tabCur]._id
		db.collection('demo').aggregate()
			.match({
				louhao
			})
			.group({
				_id: '$sushe'
			})
			.sort({
				sushe: -1 //宿舍号升序排列
			})
			.end()
			.then(res => {
				console.log(louhao + '宿舍号列表', res)
				this.setData({
					lefts: res.list
				})
				this.xuesheng()
			})
	},
	//加载当前宿舍号里所有的学生
	xuesheng() {
		let louhao = this.data.tabs[this.data.tabCur]._id
		let sushe = this.data.lefts[this.data.leftCur]._id
		db.collection('demo')
			.where({
				louhao,
				sushe
			}).get()
			.then(res => {
				console.log(louhao + sushe + '室学生列表', res)
				this.setData({
					rights: res.data
				})
			})
	},
	//顶部选择分类条目
	tabSelect(e) {
		this.setData({
			tabCur: e.currentTarget.dataset.id,
			scrollLeft: (e.currentTarget.dataset.id - 2) * 200
		}, success => {
			this.sushehao()
		})
	},
	//左侧条目选择
	switchLeftTab(e) {
		let index = e.target.dataset.index;
		this.setData({
			leftCur: index,
		}, success => {
			this.xuesheng()
		})
	},
})