NodeJs操作MongoDB教程之分页功能以及常见问题

下面给出“NodeJs操作MongoDB教程之分页功能以及常见问题”的完整攻略：

一、前言

在进行分页操作之前，需要先在 MongoDB 数据库中存入一些数据，可以使用如下示例代码：

// index.js

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/pagination-demo', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function () {
  console.log('Database connected successfully');
});

const articleSchema = new mongoose.Schema({
  title: String,
  content: String,
  created: { type: Date, default: Date.now }
});

const Article = mongoose.model('Article', articleSchema);

const articles = [
  { title: 'Article 1', content: 'Content for Article 1' },
  { title: 'Article 2', content: 'Content for Article 2' },
  { title: 'Article 3', content: 'Content for Article 3' },
  { title: 'Article 4', content: 'Content for Article 4' },
  { title: 'Article 5', content: 'Content for Article 5' },
  { title: 'Article 6', content: 'Content for Article 6' },
  { title: 'Article 7', content: 'Content for Article 7' },
  { title: 'Article 8', content: 'Content for Article 8' },
  { title: 'Article 9', content: 'Content for Article 9' },
  { title: 'Article 10', content: 'Content for Article 10' },
];

Article.insertMany(articles).then(() => {
  console.log('Data added successfully');
});

二、分页查询

1. 普通分页

在进行分页查询之前，先安装 MongoDB 的驱动程序 mongoose：

npm install mongoose

使用 mongoose 实现分页查询时可以使用如下的代码：

// pagination.js

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/pagination-demo', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function () {
  console.log('Database connected successfully');
});

const articleSchema = new mongoose.Schema({
  title: String,
  content: String,
  created: { type: Date, default: Date.now }
});

const Article = mongoose.model('Article', articleSchema);

async function getArticles(pageNumber, pageSize) {
  const count = await Article.countDocuments();
  const articles = await Article.find()
    .skip((pageNumber - 1) * pageSize)
    .limit(pageSize)
    .exec();

  return {
    totalPage: Math.ceil(count / pageSize),
    articles,
  };
}

getArticles(2, 4).then(data => {
  console.log(data);
});

2. 前端分页

如果希望在前端进行分页，可以将所有的数据查询出来，然后再根据当前页码和每页显示条数计算要显示的数据：

// pagination.js

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/pagination-demo', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function () {
  console.log('Database connected successfully');
});

const articleSchema = new mongoose.Schema({
  title: String,
  content: String,
  created: { type: Date, default: Date.now }
});

const Article = mongoose.model('Article', articleSchema);

async function getArticles() {
  const articles = await Article.find().exec();

  return {
    articles,
  };
}

getArticles().then(data => {
  console.log(data);
});

然后在前端进行渲染和分页处理。

三、常见问题

1. 数据量太大怎么办？

答：可以使用游标来实现，并且每次取出一部分数据进行渲染，这样可以避免一次性查询出大量数据，造成服务器压力过大的情况。

2. 怎样进行排序？

答：可以使用 mongoose 的 sort 方法来进行排序，示例代码如下：

async function getArticles(pageNumber, pageSize) {
  const count = await Article.countDocuments();
  const articles = await Article.find()
    .sort({ created: -1 })
    .skip((pageNumber - 1) * pageSize)
    .limit(pageSize)
    .exec();

  return {
    totalPage: Math.ceil(count / pageSize),
    articles,
  };
}

getArticles(2, 4).then(data => {
  console.log(data);
});

其中 sort({ created: -1 }) 表示按照创建时间进行倒序排序。

四、示例说明

假设现在需要在前端进行分页显示文章列表，每页显示 4 条数据，用户可以选择查看不同页码的内容，可以按照创建时间进行倒序排序。

我们可以使用如下示例代码来实现：

// pagination.js

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/pagination-demo', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = mongoose.connection;

db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function () {
  console.log('Database connected successfully');
});

const articleSchema = new mongoose.Schema({
  title: String,
  content: String,
  created: { type: Date, default: Date.now }
});

const Article = mongoose.model('Article', articleSchema);

async function getArticles(query, pageNumber, pageSize) {
  const count = await Article.countDocuments(query);
  const articles = await Article.find(query)
    .sort({ created: -1 })
    .skip((pageNumber - 1) * pageSize)
    .limit(pageSize)
    .exec();

  return {
    totalPage: Math.ceil(count / pageSize),
    articles,
  };
}

module.exports = { getArticles };

然后在前端代码中调用该方法：

// index.js

import { getArticles } from './pagination';

const pageContainer = document.querySelector('.page-container');
const pagePrevious = document.querySelector('.page-previous');
const pageNext = document.querySelector('.page-next');

let currentPage = 1;
let currentQuery = {};

function renderPage(data) {
  const totalPages = data.totalPage;
  const articles = data.articles;

  // 渲染文章列表
  // ...

  // 渲染页码
  // ...

  // 重置分页按钮状态
  if (currentPage === 1) {
    pagePrevious.disabled = true;
  } else {
    pagePrevious.disabled = false;
  }

  if (currentPage === totalPages) {
    pageNext.disabled = true;
  } else {
    pageNext.disabled = false;
  }
}

async function fetchData() {
  const data = await getArticles(currentQuery, currentPage, 4);

  renderPage(data);
}

fetchData();

pagePrevious.addEventListener('click', () => {
  if (currentPage === 1) {
    return;
  }

  currentPage--;

  fetchData();
});

pageNext.addEventListener('click', () => {
  const totalPages = pageContainer.querySelectorAll('.page').length;

  if (currentPage === totalPages) {
    return;
  }

  currentPage++;

  fetchData();
});

在上面的示例代码中，getArticles 方法接收一个查询条件、页码和每页显示的数量，然后返回符合条件的文章列表和分页信息。在前端代码中，分别监听上一页和下一页按钮的点击事件，然后根据当前页码和总页数计算要显示的数据。在渲染完数据之后，还要根据当前页码和总页数来决定上一页和下一页按钮是否可用。