How to use MongoDB with Node.js-USharing

In this tutorial I’ll show you how to interact with a MongoDB database from Node.js

We’ll be using the official mongodb npm package. If you already have a Node.js project you are working on, install it using

npm install mongodb

If you start from scratch, create a new folder with your terminal and run npm init to start up a new Node.js project, and then run the npm install mongodb command.

Connecting to MongoDB

You require the mongodb package and you get the MongoClient object from it.

const mongo = require('mongodb').MongoClient

Create a URL to the MongoDB server. If you use MongoDB locally, the URL will be something like mongodb://localhost:27017, as 27017 is the default port.

const url = 'mongodb://localhost:27017'

Then use the mongo.connect() method to get the reference to the MongoDB instance client:

mongo.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true
  }, (err, client) => {
  if (err) {
    console.error(err)
    return
  }
  //...
})

Now you can select a database using the client.db() method:

const db = client.db('kennel')

Create and get a collection

You can get a collection by using the db.collection() method. If the collection does not exist yet, it’s created.

const collection = db.collection('dogs')

Insert data into a collection a Document

Add to app.js the following function which uses the insertOne() method to add an object dogs collection.

collection.insertOne({name: 'Roger'}, (err, result) => {

})

You can add multiple items using insertMany(), passing an array as the first parameter:

collection.insertMany([{name: 'Togo'}, {name: 'Syd'}], (err, result) => {

})

Find all documents

Use the find() method on the collection to get all the documents added to the collection:

collection.find().toArray((err, items) => {
  console.log(items)
})

Find a specific document

Pass an object to the find() method to filter the collection based on what you need to retrieve:

collection.find({name: 'Togo'}).toArray((err, items) => {
  console.log(items)
})

If you know you are going to get one element, you can skip the toArray() conversion of the cursor by calling findOne():

collection.findOne({name: 'Togo'}, (err, item) => {
  console.log(item)
})

Update an existing document

Use the updateOne() method to update a document:

collection.updateOne({name: 'Togo'}, {'$set': {'name': 'Togo2'}}, (err, item) => {
  console.log(item)
})

Delete a document

Use the deleteOne() method to delete a document:

collection.deleteOne({name: 'Togo'}, (err, item) => {
  console.log(item)
})

Closing the connection

Once you are done with the operations you can call the close() method on the client object:

client.close()

Use promises or async/await

I posted all those examples using the callback syntax. This API supports promises (and async/await) as well.

For example this

collection.findOne({name: 'Togo'}, (err, item) => {
  console.log(item)
})

Can be used with promises:

collection.findOne({name: 'Togo'})
  .then(item => {
    console.log(item)
  })
  .catch(err => {
  console.error(err)
  })

or async/await:

const find = async () => {
  try {
    const item = await collection.findOne({name: 'Togo'})
  } catch(err => {
  console.error(err)
  })
}

find()

来源：https://flaviocopes.com/node-mongodb/

How to use MongoDB with Node.js