MongoDB-Tutorial

Starting & Stopping

$sudo service mongod start starts the mongodb server

$sudo service mongod stop stops the mongodb server

$sudo service mongod restart restarts the mongodb server

$mongo starts the shell

Basics

>db.help() returns the lists of command

>db.stats() returns the stats about the MongoDB client.

>use database_name it will create a new database or return if the database already exists.

>db will return the name of current database

>show dbs returns the list of all the availabel databases with there size

>db.dropDatabase() it will delete the current database

Collections

Collections: is a group of MongoDB documents. It is the equivalent of an RDBMS table. A collection exists within a single database. Collections do not enforce a schema. Documents within a collection can have different fields.

>db.createCollection(ct_name, options) It creates a new collection with name as ct_name.

Options: Specify options about memory size and indexing. This is an optional parameter.

Field	Type
capped	Boolean
autoIndexID	Boolean
size	number
max	number

>show collections displays the list of all the available collections

>db.ct_name.drop() drops the collection with the name as ct_name

Insertion

>db.ct_name.insert(document) inserts the document into the collection ct_name. We can pass a single document or an array of document in a query. _id is optional, but is specifed must be unique for every document.

	Example of single document insertion in mongodb
	```
		   >db.mycol.insert({
			   _id: ObjectId(7df78ad8902c),
			   title: 'MongoDB single query', 
			   description: 'MongoDB is no sql database',
			   tags: ['mongodb', 'database', 'NoSQL']
			})
	```

	Example of multiple document insertion in mongodb
	```
		      >db.mycol.insert([
			   {
			      title: 'MongoDB Overview', 
			      description: 'MongoDB is no sql database',
			      tags: ['mongodb', 'database', 'NoSQL'],
			   },
				
			   {
			      title: 'NoSQL Database', 
			      description: "NoSQL database doesn't have tables",
			      likes: 20, 
			      comments: [
			         {
			            user:'user1',
			            message: 'My first comment'
			         },
			         {
			            user:'user2',
			            message: 'My second comment'
			         }
			      ]
			   }
			])
	```

Search

>db.ct_name.find() will display all data in non-structured way. It is similar to select * from table_name query in sql.

>db.ct_name.find().pretty() will display all data just like above but in strucutred way.

_id will always be displayed with the find operation. To disable it, we need to set it to 0. Ex: db.ct_name.find({},{_id=0}).pretty()

Operation	Syntax	Example	Equivalent
Equality	{<key>: <value>}	db.ct_name.find({"name": "mayank"}).pretty()	name = mayank
Less than	{<key>: {$lt: <value>}}	db.ct_name.find({"age": {$lt: 100}}).pretty()	age < 100
Less than equals	{<key>: {$lte: <value>}}	db.ct_name.find({"age": {$lte: 10}}).pretty()	age <= 100
Greater than	{<key>: {$gt: <value>}}	db.ct_name.find({"age": {$gt: 50}).pretty()	age > 50
Greater than equals	{<key>: {$gte: <value>}}	db.ct_name.find({"age": {$gte:70}}).pretty()	age >= 50
Not Equals	{<key>: {$ne: <value>}}	db.ct_name.find({"age": {$ne: 50}}).pretty()	age != 50
AND	{$and: [{<key1>: <value1>},{<key2>: <value2>}]}	db.ct_name.find({$and: [{age:15},{likes:12}]).pretty()	age=15 and likes=12
OR	{$or: [{<key1>: <value1>},{<key2>: <value2>}]}	db.ct_name.find({$or: [{age:15},{likes:12}]).pretty()	age=15 or likes=12

	'''
		Select documet with either (name = mayank) or (time =1 and tags = 3)
			>db.test_db.find({$or:
				[{name:"mayank"},{
					$and:[{"time":1},
					{tags:3}]
					}
				]
			}).pretty()
	'''

For searching in sub documents we use . operator. Ex: find({< document.subdocument >:< value >"})

Update

>db.ct_name.update(selection_criteria, updation_criteria) updation can be performed using update() and save() methods. update() method updates the value in existing documents while save() method replaces the existing documents with the one passed in save() method.

We always specify $set in updation criteria. The $set operator replaces the value of a field with the specified value.

	'''
		Updates the parameter age with value 22
		 >db.test_db.update({"name":"mayank joshi"},
		 		{$set:{"age":22}
		 	},{multi:true})

		 Adds and additional value address with value to the record matching the name parameter as "mayank joshi"
		 >db.test_db.update({"name":"mayank joshi"},
		 		{$set:{"address":"newly added address"}
		 	})
	'''

By default the update() operation will only update a single document or record. To update multiple the documents we need to set parameter multi to true

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