CRUD Operations in MongoDB | NoSQL

Classified as a No SQL database , MongoDB is a scalable, open source, high performance , document-oriented database designed by keeping developers agility in mind. It is document-oriented which means that it does not store data in tables and rows as we would in relational databases like MySQL, In this we store data in JSON-like documents with dynamic schema.

In order to understand this article , you need to have :

MongoDB installed
Basic knowledge of MongoDB

In order to create a Database , use command is used.

		        
//use Your_database_name
use demo_db

After running you will observe something like this on your MongoDB CLI :

		        
>use demo_db
switched to db demo_db

As we all know , MongoDB is an Document oriented database where data is stored in the form of documents and those documents are further stored in collections. So we can create a collection using the db.createCollection() Method.

		        
//db.createCollection("Name_of_your_collection" , {Options such as Auto-indexing , size , etc }* )
// * denotes that options is an optional field.
>use demo_db
switched to db demo_db
>db.createCollection("democollection")
{ "ok" : 1 }
>

We can see the collection created by using the command show collections as shown below :

		        
>show collections
democollection
system.indexes

Creating a collection with some options in it is shown below :

		        
>db.createCollection("demoCol", {  autoIndexId : false, size : 61428,capped : true, max : 100 } )
{ "ok" : 1 }

Moreover we dont need to create collections in MongoDB because it will be automatically created when we insert some document.

MongoDB is an Document oriented database where data is stored in the form of documents. So we can insert the data into a document using the insert(document) Method. Its syntax is shown below :

		        
//db.COLLECTION_NAME.insert(document)
>use demo_db
switched to db demo_db
>db.demoCollection.insert([
   {
      Name: 'sophia', 
      Age: 23,
      sex: 'female',
      website: 'https://www.nodejsera.com',
      tags: ['mongodb', 'database', 'NoSQL']
    }
])

Inserting multiple documents using insert() command is shown below:

		        
//db.COLLECTION_NAME.insert(document)
>use demo_db
switched to db demo_db
>db.demoCollection.insert([
   {
      Name: 'sophia', 
      Age: 23,
      sex: 'female',
      website: 'https://www.nodejsera.com',
      tags: ['mongodb', 'database', 'NoSQL']
    },
	{
      Name: 'rj', 
      Age: 22,
      sex: 'male',
      website: 'https://www.nodejsera.com',
      tags: ['nodejs', 'gulpjs', 'webdeveloper']
    },
	{
      Name: 'ricky', 
      Age: 25,
      sex: 'male',
      website: 'https://www.nodejsera.com',
      tags: ['pyhton', 'machinelearning', 'expert']
    }
])

MondoDb will automatically assign each document an unique _id. _id is 12 bytes hexadecimal number unique for every document in a collection. It is generated via keeping the following format in :
_id: ObjectId(4 bytes timestamp, 3 bytes machine id, 2 bytes process id, 3 bytes incrementer)

Now we will see how we can query a document from a collection in MongoDB. So we can query the document of a collection using the find() method. Its syntax is shown below :

		        
//db.COLLECTION_NAME.find()
>use demo_db
switched to db demo_db
>db.demoCollection.find({"name":"sophia"})

{
    "_id": ObjectId(5cf87da9208b),
    "Name": "sophia", 
    "Age": 23,
    "sex": "female",
    "website": "https://www.nodejsera.com",
    "tags": ["mongodb", "database", "NoSQL"]
}
>

Operation	Syntax	Example
Equality	{:}	db.demo_collection.find({"name":"sophia"})
Less than	{:{$lt:}}	db.demo_collection.find({"age":{$lt:24}})
greater than	{:{$gt:}}	db.demo_collection.find({"age":{$gt:22}})
not equals	{:{$ne:}}	db.demo_collection.find({"age":{$ne:25}})
Less than equals	{:{$lte:}}	db.demo_collection.find({"age":{$lte:24}})
greater than equals	{:{$gte:}}	db.demo_collection.find({"age":{$gte:22}})

We can also use and & or which is explained in detail in MongoDB's respective tutorial.

We can update the document using the update() method. and in some case save() method can also be used to update the document in a collection. the syntax and example for update() is shown below :

		        
//db.COLLECTION_NAME.update(SELECTION_CRITERIA, UPDATED_DATA)
>use demo_db
switched to db demo_db
>db.demo_collection.update({'name':'sophia'},{$set:{'name':'sopia'}})
>db.demo_collection.find()
{
    "_id": ObjectId(5cf87da9208b),
    "Name": "sopia", 
    "Age": 23,
    "sex": "female",
    "website": "https://www.nodejsera.com",
    "tags": ["mongodb", "database", "NoSQL"]
}

>

This will only update the first document it will find with the matching criteria but if you want to update all the documents that matches the given criteria then we need to add an attribute in the end which is shown below :

		        
//db.COLLECTION_NAME.update(SELECTION_CRITERIA, UPDATED_DATA)
>use demo_db
switched to db demo_db
>db.demo_collection.update({'name':'sophia'},{$set:{'name':'sopia'}},{multi:true})

{multi:true} It will make sure that updation is performed on all the matching documents.

save()

It will replace the existing document completely with a new document. the syntax and example is shown below :

		        
//>db.COLLECTION_NAME.save({_id:ObjectId(),NEW_DATA})
>use demo_db
switched to db demo_db
>db.demo_collection.save(
{
	'_id': ObjectId(5cf87da9208b)
	'name':'sophia',
	'web' : 'www.nodejsera.com'
})

Now if you will check this document it consists of this new values instead of the old ones which includes age , sex, etc.

We can delete the document using the remove() method. the syntax and example is shown below :

		        
//>db.COLLECTION_NAME.remove(DELETION_CRITERIA)
>use demo_db
switched to db demo_db
>db.demo_collection.remove({'name':'sophia'})

>

Deleting just a single document. If there are multiple records matching the criteria and you want to delete just the first one out of it , then we can use this attribute of remove() method. the syntax is shown below :

		        
>db.COLLECTION_NAME.remove(DELETION_CRITERIA ,1)

Deleting all the records of the collection. it can be achieved using the following command

		        
>db.COLLECTION_NAME.remove()

What is MongoDB
Prerequisites
Create a Database
Create a Collection
Inserting data in a Document
Querying data from a Document
Updating a Document in MongoDB
Deleting a Document in MongoDB