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Connecting Node.js to MongoDB

MongoDB is a document-oriented database management system written in C++.

In this section, we will introduce how to connect to MongoDB and perform database operations using Node.js.

If you do not have basic knowledge of MongoDB, you can refer to our tutorial: MongoDB Tutorial.

Installing the Driver

This tutorial uses the custom cnpm command from Taobao for installation:

$ cnpm install mongodb

Next, we will implement the create, read, update, and delete functionalities.

Creating a Database

To create a database in MongoDB, we first need to create a MongoClient object and configure the specified URL and port number.

If the database does not exist, MongoDB will create the database and establish a connection.

Creating a Connection

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/tutorialpro";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  console.log("Database created!");
  db.close();
});

Creating a Collection

We can use the createCollection() method to create a collection:

Creating a Collection

var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/tutorialpro';
MongoClient.connect(url, function (err, db) {
    if (err) throw err;
    console.log('Database created');
    var dbase = db.db("tutorialpro");
    dbase.createCollection('site', function (err, res) {
        if (err) throw err;
        console.log("Collection created!");
        db.close();
    });
});

Database Operations (CRUD)

Unlike MySQL, MongoDB automatically creates databases and collections, so we do not need to manually create them before use.

Inserting Data

The following example connects to the database tutorialpro and the site collection, and inserts a single data entry using insertOne():

Inserting a Single Data Entry

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var myobj = { name: "tutorialpro.org", url: "www.tutorialpro" };
    dbo.collection("site").insertOne(myobj, function(err, res) {
        if (err) throw err;
        console.log("Document inserted successfully");
        db.close();
    });
});

Executing the following command outputs the result:

$ node test.js
Document inserted successfully

From the output, it is clear that the data has been inserted successfully.

We can also open the MongoDB client to view the data, such as:

> show dbs
tutorialpro  0.000GB          # Automatically created the tutorialpro database
> show tables
site                     # Automatically created the site collection (table)
> db.site.find()
{ "_id" : ObjectId("5a794e36763eb821b24db854"), "name" : "tutorialpro.org", "url" : "www.tutorialpro" }
>

To insert multiple entries, use insertMany():

Inserting Multiple Data Entries

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var myobj = [
        { name: 'tutorialpro1.org', url: 'www.tutorialpro1' },
        { name: 'tutorialpro2.org', url: 'www.tutorialpro2' },
        { name: 'tutorialpro3.org', url: 'www.tutorialpro3' }
    ];
    dbo.collection("site").insertMany(myobj, function(err, res) {
        if (err) throw err;
        console.log("Number of documents inserted: " + res.insertedCount);
        db.close();
    });
});

Executing the following command outputs the result:

$ node test.js
Number of documents inserted: 3

From the output, it is clear that the data has been inserted successfully.

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var myobj = [
        { name: 'tutorialpro', url: 'https://c.tutorialpro.org', type: 'cn' },
        { name: 'Google', url: 'https://www.google.com', type: 'en' },
        { name: 'Facebook', url: 'https://www.google.com', type: 'en' }
    ];
    dbo.collection("site").insertMany(myobj, function(err, res) {
        if (err) throw err;
        console.log("Number of documents inserted: " + res.insertedCount);
        db.close();
    });
});

res.insertedCount is the number of inserted documents.

Query Data

You can use find() to retrieve data, find() returns all data that matches the criteria. If no criteria are specified, find() returns all data in the collection.

find()

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    dbo.collection("site").find({}).toArray(function(err, result) { // Returns all data in the collection
        if (err) throw err;
        console.log(result);
        db.close();
    });
});

The following example retrieves instances where the name is "tutorialpro.org":

Query Data with Specific Criteria

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var whereStr = { "name": 'tutorialpro.org' };  // Query criteria
    dbo.collection("site").find(whereStr).toArray(function(err, result) {
        if (err) throw err;
        console.log(result);
        db.close();
    });
});

Executing the following command outputs the result:

[ { _id: 5a794e36763eb821b24db854,
    name: 'tutorialpro.org',
    url: 'www.tutorialpro' } ]

Update Data

We can also modify data in the database. The following example changes the url to https://www.tutorialpro.org for the name "tutorialpro.org":

Update a Single Document

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var myquery = { name: "tutorialpro.org" };
    var newvalues = { $set: { url: "https://www.tutorialpro.org" } };
    dbo.collection("site").updateOne(myquery, newvalues, function(err, res) {
        if (err) throw err;
        console.log("Document updated");
        db.close();
    });
});

var whereStr = {"name":'tutorialpro.org'};  // Query condition
var updateStr = {$set: { "url" : "https://www.tutorialpro.org" }};
dbo.collection("site").updateOne(whereStr, updateStr, function(err, res) {
    if (err) throw err;
    console.log("Document updated successfully");
    db.close();
});

After successful execution, check the data modification in the mongo management tool:

> db.site.find().pretty()
{
    "_id" : ObjectId("5a794e36763eb821b24db854"),
    "name" : "tutorialpro.org",
    "url" : "https://www.tutorialpro.org"     // Modified to https
}

To update all documents that match the criteria, use updateMany():

Update Multiple Documents

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var whereStr = {"type":'en'};  // Query condition
    var updateStr = {$set: { "url" : "https://www.tutorialpro.org" }};
    dbo.collection("site").updateMany(whereStr, updateStr, function(err, res) {
        if (err) throw err;
        console.log(res.result.nModified + " documents updated");
        db.close();
    });
});

result.nModified indicates the number of documents updated.

Delete Data

The following example deletes the data where name is "tutorialpro.org":

Delete One Document

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var whereStr = {"name":'tutorialpro.org'};  // Query condition
    dbo.collection("site").deleteOne(whereStr, function(err, obj) {
        if (err) throw err;
        console.log("Document deleted successfully");
        db.close();
    });
});

After successful execution, check the data deletion in the mongo management tool:

> db.site.find()
>

To delete multiple documents, use the deleteMany() method:

Delete Multiple Documents

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
    if (err) throw err;
    var dbo = db.db("tutorialpro");
    var whereStr = { type: "en" };  // Query condition
    dbo.collection("site").deleteMany(whereStr, function(err, obj) {
        if (err) throw err;
        console.log("Documents deleted successfully");
        db.close();
    });
});

console.log(obj.result.n + " documents deleted"); db.close(); }); });


The number of documents deleted is obj.result.n.

### Sorting

Sorting uses the `sort()` method, which accepts a parameter specifying ascending (1) or descending (-1) order.

For example:

{ type: 1 } // Sort by type field in ascending order { type: -1 } // Sort by type field in descending order


Sort by type in ascending order:

## Sorting

var MongoClient = require('mongodb').MongoClient; var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) { if (err) throw err; var dbo = db.db("tutorialpro"); var mysort = { type: 1 }; dbo.collection("site").find().sort(mysort).toArray(function(err, result) { if (err) throw err; console.log(result); db.close(); }); });


### Pagination

To set a specified number of returned documents, you can use the `limit()` method, which accepts one parameter specifying the number of documents to return.

## limit(): Read two documents

var MongoClient = require('mongodb').MongoClient; var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) { if (err) throw err; var dbo = db.db("tutorialpro"); dbo.collection("site").find().limit(2).toArray(function(err, result) { if (err) throw err; console.log(result); db.close(); }); });


To specify the number of documents to skip, you can use the `skip()` method.

## skip(): Skip the first two documents and read two documents

var MongoClient = require('mongodb').MongoClient; var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) { if (err) throw err; var dbo = db.db("tutorialpro"); dbo.collection("site").find().skip(2).limit(2).toArray(function(err, result) { if (err) throw err; console.log(result); db.close(); }); });


### Join Operations

MongoDB is not a relational database, but we can use `$lookup` to perform a left join.

For example, we have two collections with the following data:

Collection 1: orders

[ { _id: 1, product_id: 154, status: 1 } ]


Collection 2: products

[ { _id: 154, name: 'Laptop' }, { _id: 155, name: 'Headphones' }, { _id: 156, name: 'Desktop Computer' } ]


## $lookup to perform a left join

var MongoClient = require('mongodb').MongoClient; var url = "mongodb://127.0.0.1:27017/";

MongoClient.connect(url, function(err, db) { if (err) throw err; var dbo = db.db("tutorialpro"); dbo.collection('orders').aggregate([ { $lookup: { from: 'products', // Right collection

localField: 'product_id',    // Left collection join field
foreignField: '_id',         // Right collection join field
as: 'orderdetails'           // New field (array type)
}
}
]}).toArray(function(err, res) {
if (err) throw err;
console.log(JSON.stringify(res));
db.close();
});
});

Deleting a Collection

We can use the drop() method to delete a collection:

drop()

var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";

MongoClient.connect(url, function(err, db) {
if (err) throw err;
var dbo = db.db("tutorialpro");
// Delete the 'test' collection
dbo.collection("test").drop(function(err, delOK) {  // delOK returns true if successful, otherwise false
if (err) throw err;
if (delOK) console.log("Collection deleted");
db.close();
});
});

Using Promise

Promise is a class provided by ECMAScript 6 to write complex asynchronous tasks more elegantly.

If you are not familiar with Promise, you can refer to JavaScript Promise.

The following example uses Promise to create a collection:

Example

const MongoClient = require("mongodb").MongoClient;
const url = "mongodb://localhost/tutorialpro";
MongoClient.connect(url).then((conn) => {
console.log("Database connected");
var dbase = conn.db("tutorialpro");
dbase.createCollection("site").then((res) => {
console.log("Collection created");
}).catch((err) => {
console.log("Database operation error");
}).finally(() => {
conn.close();
});
}).catch((err) => {
console.log("Database connection failed");
});

Promise Data Operations

Now we will perform four consecutive operations in a program: add, query, update, delete.

Example

const MongoClient = require("mongodb").MongoClient;
const url = "mongodb://localhost/";
MongoClient.connect(url).then((conn) => {
console.log("Database connected");
const test = conn.db("testdb").collection("test");
// Add
test.insertOne({ "site": "tutorialpro.org" }).then((res) => {
// Query
return test.find().toArray().then((arr) => {
console.log(arr);
});
}).then(() => {
// Update
return test.updateMany({ "site": "tutorialpro.org" },
{ $set: { "site": "example.com" } });
}).then((res) => {
// Query
return test.find().toArray().then((arr) => {

console.log(arr);
});
}).then(() => {
    // Delete
    return test.deleteMany({ "site": "example.com" });
}).then((res) => {
    // Query
    return test.find().toArray().then((arr) => {
        console.log(arr);
    });
}).catch((err) => {
    console.log("Data operation failed: " + err.message);
}).finally(() => {
    conn.close();
});
}).catch((err) => {
    console.log("Database connection failed");
});

Execution result:

Database connected
[ { _id: 5f1664966833e531d83d3ac6, site: 'tutorialpro.org' } ]
[ { _id: 5f1664966833e531d83d3ac6, site: 'example.com' } ]
[]

Implementing the same data operation using async functions

Example

const MongoClient = require("mongodb").MongoClient;
const url = "mongodb://localhost/";

async function dataOperate() {
    var conn = null;
    try {
        conn = await MongoClient.connect(url);
        console.log("Database connected");
        const test = conn.db("testdb").collection("test");
        // Add
        await test.insertOne({ "site": "tutorialpro.org" });
        // Query
        var arr = await test.find().toArray();
        console.log(arr);
        // Update
        await test.updateMany({ "site": "tutorialpro.org" },
            { $set: { "site": "example.com" } });
        // Query
        arr = await test.find().toArray();
        console.log(arr);
        // Delete
        await test.deleteMany({ "site": "example.com" });
        // Query
        arr = await test.find().toArray();
        console.log(arr);
    } catch (err) {
        console.log("Error: " + err.message);
    } finally {
        if (conn != null) conn.close();
    }
}

dataOperate();

Running result:

Database connected
[ { _id: 5f169006a2780f0cd4ea640b, site: 'tutorialpro.org' } ]
[ { _id: 5f169006a2780f0cd4ea640b, site: 'example.com' } ]
[]

The running results are exactly the same.

Clearly, async functions are a very good programming style and are very useful when using asynchronous operations multiple times.

However, do not use async functions in node.js versions below 7.6.0. ```

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