/GettingStartedWithMongoDB

This repository contains notes related to MongoDB. Learning to use MongoDB native driver library to perform CRUD operations.

Getting Started With MongoDB

This repository contains notes related to MongoDB.

Objectives

  • Learning to use MongoDB native driver.
  • Learning to CREATE, READ, UPDATE and DELETE documents from the collection in MongoDB using MongoDB native driver library

Installation Steps in Windows

  1. Go to https://www.mongodb.com
  2. Go to downloads
  3. Select Community server OR navigate to https://www.mongodb.com/download-center?jmp=nav#community
  4. Select the first version appears on the dropdown menu i.e. Windows server 2008 R2 64-bit and later, with SSL support x64
  5. Once you have downloaded the installer, open it and click next, select complete setup option to install.

Starting the MongoDB Server

  • After the software is installed, navigate into command prompt and boot up the server.
    • Navigate into program files -> MongoDB -> server -> 3.6 -> bin This folder contains all executables to start up the server and connect to it Example-> mongod.exe => This starts local MongoDB database

  • Before we execute any executable, we need to create a directory where all of our data can get stored. For this, I have created a folder named mongo-data in my user directory where the data is going to get stored.
    • This is the path we need to specify when we execute mongod.exe (We need to tell the mongo where to store the data)

  • By executing this command, you start up the server

  • Now, the server has started on port - 27017
  • Let's create and read data. Open another command prompt and go to bin folder insider MongoDB folder. Run mongo.exe This connects to local MongoDB database
  • You can try inserting data to database and try fetching inserted data for testing purpose.

NoSQL Database

  • In relational databases, we have relation/table whereas in NoSQL databases we have collection
  • In relational databases, we have rows/records whereas in NoSQL databases we have document
  • In relational databases, individual properties are called columns. It is schema based. So whatever you specify in the schema has to be present for all the records. In case of NoSQL databases, the documents in the collection don't need to have the same properties.The properties are called fields

Connecting to MongoDB database from inside of NodeJS application

npm install mongodb@2.2.5 --save
  • MongoClient from mongodb library lets you connect to the mongo server and issue command to manipulate the database

Code Snippet => Simply connecting to MongoDB database from inside of NodeJS aplication

// Loading the library
const MongoClient = require('mongodb').MongoClient;

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }

  console.log('Connected to MongoDB server.');

  // Close the connection with MongoDB Server
  db.close();
});

You can give URL of the database that doesn't exist. MongoDB will form the connection but will not create a database, until we add data to it.


## Insert Data into database

Code Snippet => Inserting a document into MongoDB database using NodeJs 

// loading the library
const MongoClient = require('mongodb').MongoClient;

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }
  console.log('Connected to MongoDB server.');

  // Inserting new record to collection
  db.collection('Todos').insertOne({
    text: 'My first to-do',
    completed: false
  }, (err, result) => {
    if(err) {
      return console.log('Unable to insert todo', err);
    }

    // result Contains the result document from MongoDB
    // ops Contains the documents inserted with added _id fields
    console.log(JSON.stringify(result.ops, undefined, 2));
  });


  // Close the connection with MongoDB Server
  db.close();
});

Output of the above code snippet in command prompt

Now, checking the generation of collection and document in MongoDB Compass.
In the following image,

  • Database Name is TodoApp
  • Collection is Todos
  • Document is the data record which is inserted.


Now, let's try adding one more collection - Users to TodoApp database

  // Inserting new record to collection - Users
  db.collection('Users').insertOne({
    name: 'Ankita',
    age: 23,
    location: 'TX'
  }, (err, result) => {
    if(err) {
      return console.log('Unable to insert user', err);
    }
    console.log(JSON.stringify(result.ops, undefined, 2));
  });


Exploring ObjectId

  • ObjectId is randomly generated id used to uniquely identify every document in MongoDB databases
  • MongoDB databases can be scaled out. Scaling out means you add more database servers to handle the extra load.
  • When we use randomly generated id we don't need to constantly communicate with other database servers to check what the highest incrementing value is.
  • ObjectId is a 12 byte value where the first 4 bytes are a timestamp, next 3 bytes are machine identifiers (If 2 computers generate ObjectIds, then they will have machine identifier to ensure that id generated is unique), next 2 bytes are process id and lastly we have 3 bytes counter.

Fetch data from database/ Querying data from NodeJS

  • Collection is accessed using find(). find() returns mongodb cursor (Pointer to documents)
// loading the library
const MongoClient = require('mongodb').MongoClient;

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }
  console.log('Connected to MongoDB server.');

  // Access the collection
  db.collection('Todos').find().toArray().then((docs) => {
    console.log('Todos');
    console.log(JSON.stringify(docs, undefined, 2));
  }, (err) => {
    console.log('Unable to fetch todos', err);
  });

});

Deleting documents

Using deleteMany() -> targets many documents and remove them
For this scenario, I have cloned one document entry thrice in the database. 

// loading the library
// const MongoClient = require('mongodb').MongoClient;
const {MongoClient, ObjectID} = require('mongodb');

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }
  console.log('Connected to MongoDB server.');

  // deleteMany() -> targets many documents and remove them
   db.collection('Todos').deleteMany({text:'Go to Walmart'}).then((result) => {
     console.log(result);
   });

  // db.close();
});

Output,

Using deleteOne() -> targets one documents and removes it.
For this scenario, I have cloned a document entry twice in the database

// loading the library
// const MongoClient = require('mongodb').MongoClient;
const {MongoClient, ObjectID} = require('mongodb');

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }
  console.log('Connected to MongoDB server.');

   // deleteOne() -> targets one documents and removes it
   db.collection('Todos').deleteOne({text:'Submit job applications'}).then((result) => {
     console.log(result);
   });

  // db.close();

Output,
Using findOneAndDelete() -> removes individual item and also returns those values. 

// loading the library
// const MongoClient = require('mongodb').MongoClient;
const {MongoClient, ObjectID} = require('mongodb');

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }
  console.log('Connected to MongoDB server.');

   // findOneAndDelete() -> removes individual item and also returns those values
  // targetting todos with completed: false
  db.collection('Todos').findOneAndDelete({completed:false}).then((result) => {
    console.log(result);
  });

  // db.close();

Output,

Updating the data i.e. updating the documents in the MongoDB collection

Let's try setting the completed value to true for the text 'Complete ML assignment'

// loading the library
// const MongoClient = require('mongodb').MongoClient;
const {MongoClient, ObjectID} = require('mongodb');

// Connection URL (to connect to database/ URL of the location where database lives)
const url = 'mongodb://localhost:27017/TodoApp';

// Connecting to the database using MongoClient
MongoClient.connect(url, (err, db) => {
  if(err) {
    return console.log('Unable to connect to MongoDB server');
  }
  console.log('Connected to MongoDB server.');

  // findOneAndUpdate() -> It lets us update an item and get the new document back.
  // findOneAndUpdate(filter, update, options, callback) => returns Promise if no callback passed
  db.collection('Todos').findOneAndUpdate({
    _id: new ObjectID('5aaaed348efdc64dd438e6f1')
  }, {
    $set: {
      completed: true
    }
  }, {
    returnOriginal: false //returns the updated document
  }).then((result) => {
    console.log(result);
  })
  // db.close();
});

Using mongoose to query your data

Let's consider that, we have following documents in MongoDB and we want to fetch a document with id 5ab2e99dde119c582e569820, 

    const {mongoose} = require('./../server/db/mongoose');
    const {Todo} = require('./../server/models/todo');

    var id = '5ab2e99dde119c582e569820';

    Todo.find({
      _id: id
    }).then((todos) => {
      console.log('Todos using find()', todos);
    });

    // To be used when you want to find one document by something other than ID
    Todo.findOne({
      _id: id
    }).then((todo) => {
      console.log('Todo using findOne()', todo);
    });

    // To look for a document just by identifier
    Todo.findById(id).then((todo) => {
      console.log('Todo by ID', todo);
    });

Output,
For more information refer, http://mongoosejs.com/docs/queries.html


Now handling the case where, id is incorrect or it is not in the collection To demonstrate, I have tweaked the id in above code snippet, so the result would be

Now here, we can observe that, the result returned is either empty array or null value when the id does not match anything in the database. This implies that, the error is not going to get thrown as it is still firing the success case either with empty array or null and therefore we have to handle the case in our code where id doesn't match.

  Todo.findById(id).then((todo) => {
  // Handling the case where id doesn't match
      if(!todo) {
        return console.log('Id not found');
      }
    console.log('Todo by ID', todo);
  });

Now validating the case where ID is invalid - In order to validate object ID we can try catch block - To demonstrate this case, I have appended few digits to existing object id

  **Method 1**
  
  ```
    var id = '5ab2e99dde119c582e569820888';

    Todo.findById(id).then((todo) => {
      if(!todo) {
        return console.log('Id not found');
      }
      console.log('Todo by ID', todo);
     }).catch((e) => {
        console.log(e);
    });
  
  ```

Output,

Hence, above error states that the id that you are trying to find doesn't exist.

Method 2
With the help of MongoDB native driver

const {ObjectID} = require('mongodb');

var id = '5ab2e99dde119c582e569820888';

 if(!ObjectID.isValid(id)) {
   console.log('ID not valid');
 }
 
 Todo.findById(id).then((todo) => {
   if(!todo) {
     return console.log('Id not found');
   }
   console.log('Todo by ID', todo);
   }).catch((e) => {
     console.log(e);
   });

Output,