Getting Started With MongoDB Shell & Basic Commands

MongoDB shell commands

Below are a few MongoDB shell commands that you can begin familiarizing yourself with.

• Install Mongosh on Mac using the command line.

brew install mongosh

Your default local port for Mongod will be 27017

• To change the default port you can use the following command,

mongosh --port 28015

• To check the local Database list, use the command below.

type db in terminal

• Finally, to select the database from the list, use the following command,

type use "<database name>" in terminal

MongoDB CRUD operation commands

Moving on we can perform some basic operations on MongoDB shell.

Create

• Insert one

To insert a single document, type the following command in MongoDB shell command terminal.

db.users.insertOne(
 {
   fullName: "The Favourite",
   email: [ "Drama", "History" ],
   subscription: 1
   isBlocked: false,
 }
)

• Insert many

To insert many documents at a single go, type the following command in MongoDB shell command terminal.

db.subscriptios.insertMany([
  {
   title: Basic,
   price: free,
   expire: 0,
   details: “”
  {
   title: glory,
   price: 10$,
   expire: 0,
   details: “”
  {
   title: premium,
   price: 50$,
   expire: 0,
   details: “”
  },
])

Update

• Update one

To update a single document, type the following command in MongoDB shell command terminal.

db.users.updateOne( { _id: "" },
{
 $set: {
   fullName: "Faraz Ahmed”
 }
})

• Update many

To update many documents in a single go, type the following command in the MongoDB shell command terminal.

db.movies.updateMany(
 { price: { $lt: 50 } },
 {
   $set: { access: free, access_expire: 30 }
 }
)

Delete

• Delete one

To delete document, type the following command in MongoDB shell command terminal.

db.movies.deleteOne( { _id: "" } )

• Delete many

To delete documents many documents in a single go, type the following command in the MongoDB shell command terminal.

db.movies.deleteMany( { createdAt: { $ls: ""} } )

Get / Get all

• Find all

To find all the documents from the collection, type the following command in the MongoDB shell command terminal.

db.movies.find()

• Find selective

To get selective documents from the collection, type the following command in the MongoDB shell command terminal.

db.movies.find( { "genre": "Action" } )

• Switch to another database

If you want to switch to another database temporarily, you can do it by running the following MongoDB shell commands.

db.getSiblingDB(<database name>).getCollectionNames();

Use of different conditional operators for queries like “and/or”

Example

db.movies.find( { genre: "Action", "rating": { $gte: 7 } } )
db.movies.find({
year: 2010,
$or: [ { "rating.wins": { $gte: 5 } }, { genres: "Drama" } ]
})

You can build a pipeline of queries/filtering to get specific data from the collection.

Example

db.orders.aggregate( [

// Stage 1: Filter pizza order documents by pizza size
{
$match: { size: "medium" }
},
// Stage 2: Group remaining documents by pizza name and calculate total quantity
{
$group: { _id: "$name", totalQuantity: { $sum: "$quantity" } }
}
] )

On the first stage of the pipeline we will be filtering the data with a matching keyword where size is “medium”, then on the second stage we are grouping the filtered data with a “group” keyword.

Indexes

MongoDB utilizes indexes, which are data structures, designed to enhance query performance by facilitating efficient data retrieval from collections. Indexes store a condensed version of selected fields or values from the data, enabling the database to swiftly locate the desired documents. This optimization process significantly improves the efficiency of querying operations.

to create a ascending index

db.records.createIndex( { score: 1 } )

to create a descending index

db.records.createIndex( { score: -1 } )

We can create multi keys indexes, text indexes, wildcard indexes and much more.

Lookups

Just like the join function in other databases like MySQL, you can also perform the join functionality in MongoDB.

Syntax

To join between collections we can use “lookup”.

{$lookup:
     {
        from: <joined collection>,
        let: { <var_1>: <expression>, …, <var_n>: <expression> },
        pipeline: [ <pipeline to run on joined collection> ],
        as: <output array field>
     }
}

Sample post table

{
    "title" : "my first post",
    "author" : "Jim",
    "likes" : 5
},
{
    "title" : "my second post",
    "author" : "Jim",
    "likes" : 2
},
{
    "title" : "hello world",
    "author" : "Joe",
    "likes" : 3
}

Sample comment table

{
    "postTitle" : "my first post",
    "comment" : "great read",
    "likes" : 3
},
{
    "postTitle" : "my second post",
    "comment" : "good info",
    "likes" : 0
},
{
    "postTitle" : "my second post",
    "comment" : "i liked this post",
    "likes" : 12
},
{
    "postTitle" : "hello world",
    "comment" : "not my favorite",
    "likes" : 8
},
{
    "postTitle" : "my last post",
    "comment" : null,
    "likes" : 0
}

Sample “lookup”

db.posts.aggregate([
    { $lookup:
        {
           from: "comments",
           localField: "title",
           foreignField: "postTitle",
           as: "comments"
        }
    }
])

You can also add a pipeline and run a multi-level query in a single aggregate.

Local DB connectivity

Connect local MongoDB to your local backend application.

Here we are connecting the local MongoDB to the node.js application, on which we will execute the above operations and more using the MongoDB shell.

const mongoose = require('mongoose');
const URI = mongodb://localhost:<local port number>/<database name>;
const connectDB = async () => {
    await mongoose.connect(URI, { useUnifiedTopology: true, useNewUrlParser: true })
    console.log("connected...!")
}
module.exports = connectDB;

After this, you can perform different operations in your local MongoDB database.

Conclusion

As enterprise-level applications continue to evolve, MongoDB is increasingly recognized as a vital tool for data storage. If you are interested in getting started with MongoDB CLI, this article serves as a comprehensive guide to help you grasp the fundamentals of MongoDB.