Databases, Collections and Documents in MongoDB

As discussed in the previous post we learned to install and connect to MongoDB from the command line

In this post will go ahead with creating a Database, Collection, and Documents and perform different operations in MongoDB

Create Database

Connect to MongoDB on the command line by using the "mongo" command

Creating a mongo database is just like creating a directory structure, in the below example I have created a database named "techon_db"

Below screenshot will show the steps

We can see "use " command will be able to create a database and same way we can switch to another database as well

"db" command will show the current db and show dbs will list all the databases present in an instance with some data in it. The empty database will not be shown here.

Drop Database

In the similar way, dropping of db is very simple, just invoke db.dropDatabase(); from the database, you want to drop

> use mydb

switched to db mydb

> db.dropDatabase ();

{ "ok" : 1 }

Create Collection

As mentioned Introduction of MongoDB, the collection is analogous to a table in RDMBS and is created using BSON (binary JSON) coding, here we will create a simple collection under our recently created db "techon_db"

There is a couple of ways to do it.

1. Using db.createCollection ("collectionname")

I have created a collection with the name "techon_col" and you can see the same as shown below 

>use techon_db;

switched to db techon_db

> 

>show collections;

> 

>db.createCollection ("techon_col");

{"ok" : 1 }

>show collections;

techon_col

2. By inserting documents in collection

In the below example, we are creating collection techon_col1 and inserting documents in it. This method performs both steps within a single command. It will automatically create a collection and insert a document in it

>show dbs;

admin      0.000GB

config     0.000GB

local      0.000GB

techon_db  0.000GB

> 

>db

techon_db

>show collections;

techon_col

> 

>db.techon_col1.insert({name: "John"});

WriteResult({"nInserted" : 1 })

> 

>show collections;

techon_col

techon_col1

Dropping Collection

In the below example I have dropped collection techon_col1.

>show collections

techon_col

techon_col1

>db.techon_col1.drop();

true

>show collections

techon_col

Insert and Remove Documents

Now we will try to insert data in collection techon_col, first, check if it has any data in it using find ()

>use techon_db

switched to db

techon_db

>show collections;

techon_col

techon_col1

>db.techon_col1.find();

{"_id" : ObjectId("5bfa6a9a131a6cd76ed5cd4c"),"name" : "John" }

>db.techon_col.find();

>

We can see there is no document in the techon_col collection

Below I have added two documents in the collection with three attributes 

Rno,

firstname and 

lastname. 

"_id" is the default attribute generated by MongoDB,it will work as primary key

db.techon_col.find();

> 

>db.techon_col.insert({"Rno":"10",

"firstname":"Mark",

"lastname":"steve"});

WriteResult({"nInserted" : 1 })

> 

>db.techon_col.insert({"Rno":"11",

"firstname":"Dave",

"lastname":"john"});

WriteResult({"nInserted" : 1 })

> 

>db.techon_col.find();

{"_id" : ObjectId("5bfa7162131a6cd76ed5cd4f"),

"Rno" : "10", "firstname" : "Mark",

"lastname" : "steve" }

{"_id" : ObjectId("5bfa718a131a6cd76ed5cd50"),

"Rno" : "11", "firstname" : "Dave",

"lastname" : "john" }

>

Removing Document

In below example I have removed document with Rno 10

>db.techon_col.remove({"Rno":"10"});

WriteResult({"nRemoved" : 1 })

>db.techon_col.find();

{"_id" : ObjectId("5bfa718a131a6cd76ed5cd50"),

"Rno" : "11", "firstname" : "Dave",

"lastname" : "john" }

>

Here is the summary screenshot of activities we have performed

[Also read - CRUD operations in Mongodb]

In case you want to check basics of MongoDB, Visit Introduction to MongoDB