Mongo DB

What is
MongoDB?
MongoDB is a document-oriented NoSQL
database used for high volume data storage.
MongoDB is a database which came into light
around the mid-2000s. It falls under the category
of a NoSQL database. Unlike in SQL databases,
where you must have a table's schema declared
before inserting data, MongoDB's collections do
not enforce document structure.This sort of
flexibility is what makes MongoDB so powerful.

MongoDB
Features
1. Each database contains collections which in turn contains
documents. Each document can be different with a varying
number of fields.The size and content of each document can
be different from each other.
2. The document structure is more in line with how developers
construct their classes and objects in their respective
programming languages. Developers will often say that their
classes are not rows and columns but have a clear structure
with key-value pairs.
3. As seen in the introduction with NoSQL databases, the rows
(or documents as called in MongoDB) doesn't need to have a
schema defined beforehand. Instead, the fields can be created
on the fly.
4. The data model available within MongoDB allows you to
represent hierarchical relationships, to store arrays, and other
more complex structures more easily.

Key
Components
of MongoDB
Architecture
1. _id – This is a field required in every MongoDB
document. The _id field represents a unique value in
MongoDB document. The _id field is like the
primary key. If you create a new document without
MongoDB will automatically create the field. So for
we see the example of the above customer table,
will add a 24 digit unique identifier to each
collection.
2.Collection – This is a grouping of MongoDB
documents. A collection is the equivalent of a table
created in any other RDMS such as Oracle or MS SQL.
collection exists within a single database. As seen
introduction collections don't enforce any sort of
3.Cursor – This is a pointer to the result set of a query.
Clients can iterate through a cursor to retrieve results.

Key
Components
of MongoDB
Architecture
1. Database – This is a container for collections like in RDMS
wherein it is a container for tables. Each database gets its
files on the file system. A MongoDB server can store
databases.
2.Document - A record in a MongoDB collection is basically
called a document. The document, in turn, will consist of
and values.
3.Field - A name-value pair in a document. A document has
zero or more fields. Fields are analogous to columns in
databases.The following diagram shows an example of
Key value pairs. So in the example below CustomerID and
the key value pair's defined in the document.
4.JSON – This is known as JavaScript Object Notation. This is
a human-readable, plain text format for expressing
JSON is currently supported in many programming

Why Use
MongoDB
1.Document-oriented – Since MongoDB is a NoSQL type
database, instead of having data in a relational type
format, it stores the data in documents. This makes
MongoDB very flexible and adaptable to real business
world situation and requirements.
2.Ad hoc queries - MongoDB supports searching by field,
range queries, and regular expression searches. Queries
can be made to return specific fields within documents.
3.Indexing - Indexes can be created to improve the
performance of searches within MongoDB. Any field in a
MongoDB document can be indexed.

Why Use
MongoDB
1.Replication - MongoDB can provide high availability
with replica sets. A replica set consists of two or
DB instances. Each replica set member may act in
the primary or secondary replica at any time. The
replica is the main server which interacts with the
performs all the read/write operations. The
maintain a copy of the data of the primary using
replication. When a primary replica fails, the replica
automatically switches over to the secondary and
becomes the primary server.
2.Load balancing - MongoDB uses the concept of
sharding to scale horizontally by splitting data
MongoDB instances. MongoDB can run over multiple
balancing the load and/or duplicating data to keep
up and running in case of hardware failure.

Install
MongoDB
 CMD command to install mongodb after Download
it:
npm install mongodb --save

Create
Database
 To create a database in MongoDB, First create a
MongoClient object and specify a connection URL with
the correct ip address and the name of the database
which you want to create.
 MongoDB will automatically create the database if it
does not exist, and make a connection to it.
Example
 Create a folder named "MongoDatabase" as a database.
Suppose you create it on Desktop. Create a js file named
"createdatabase.js" within that folder and having the
following code:

Example
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/MongoDatbase";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
console.log("Database created!");
db.close();
});

Create
Collection
 MongoDB is a NoSQL database so data is stored in
collection instead of table. createCollection
method is used to create a collection in MongoDB.
 Example
 Create a collection named "employees".

Example
var url = "mongodb://localhost:27017/ MongoDatabase";
if (err) throw err;
db.createCollection("employees", function(err, re) {
if (err) throw err;
console.log("Collection is created!");
db.close();
});
});

Insert Record
insertOne()
if (err) throw err;
var myobj = { name: "Ajeet Kumar", age: "28", address: "De
lhi" };
db.collection("employees").insertOne(myobj, function(err, res
)
{
if (err) throw err;
console.log("1 record inserted");
db.close();
});
});

Insert Multiple
Records
insert()
if (err) throw err;
var myobj = [
{ name: "Mahesh Sharma", age: "25", address: "Ghaziabad"},
{ name: "Tom Moody", age: "31", address: "CA"},
{ name: "Zahira Wasim", age: "19", address: "Islamabad"},
{ name: "Juck Ross", age: "45", address: "London"}
];
db.collection("customers").insert(myobj, function(err, res) {
if (err) throw err;
console.log("Number of records inserted: " + res.insertedCount);
db.close();
});
});

Select Record
findOne()
var http = require('http');
var url = "mongodb://localhost:27017/MongoDatabase";
if (err) throw err;
db.collection("employees").findOne({}, function(err, result) {
if (err) throw err;
console.log(result.name);
db.close();
});
});

Select Multiple
Records
find()
if (err) throw err;
db.collection("employees").find({}).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});

Filter Query
find()
This method is also used to filter the result on a specific parameter.
if (err) throw err;
var query = { address: "Delhi" };
db.collection("employees").find(query).toArray(function(err, result)
{
if (err) throw err;
db.close();
});
});

Filter With Regular
Expression
Retrieve the record from the collection where address start with
letter "L".
if (err) throw err;
var query = { address: /^L/ };
db.collection("employees").find(query).toArray(function(err, result)
{
if (err) throw err;
db.close();
});
});

Sorting
sort()
Sort in Ascending Order
if (err) throw err;
var mysort = { name: 1 };
db.collection("employees").find().sort(mysort).toArray(function(err, result)
{
if (err) throw err;
db.close();
});
});

Remove
remove()
if (err) throw err;
var myquery = { address: 'Ghaziabad' };
db.collection("employees").remove(myquery, function(err, obj) {
if (err) throw err;
console.log(obj.result.n + " record(s) deleted");
db.close();
});
});

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