Mongoose

Mongoose is an object modeling package for Node that essentially works like an ORM (Object-relational mapping ) that you would see in other languages.
Mongoose allows us to have access to the MongoDB commands for CRUD simply and easily.

Mongoose Installation

npm install mongoose --save

Now that we have the package, we just
have to grab it in our project

var mongoose = require('mongoose');

We also have to connect to a MongoDB database (either local or hosted)

mongoose.connect('mongodb://localhost/myappdatabase');

Terminology of Mongoose

Mongoose will use the terms Schema
and Model.

What is Schema?

"Mongoose Schema will create a mongodb collection and defines the shape of the documents within that collection".

If we want to create a mongodb collection in a structured manner similar to SQL tables then we can do that using mongoose Schema.

In the schema creation we will specify the details of fields like field name, its type, default value if need, index concept if need, constraint concept if need.

What is Model?

Schemas define a structure we will apply that Schema part to a model, means "Models are the constructors compiled from our schema
definitions".

Instances of these models represent documents which can be saved and retrieved from our database. All document creation and retrieval from the database is handled by these models

Key Methods and Properties of Mongoose

Connect() :- Opens the default mongoose
connection.

CreateConnection()  :- Will creates a connection
instance and its work is similar to connect()

Schema() :- The Mongoose Schema constructor

Model() :- The Mongoose Model constructor

Document() :- The Mongoose Document constructor.

Disconnect() :-  Disconnects all connections.

Mongoose Connection

Open(): Opens the connection to MongoDB.

OpenSet(): Opens the connection to a replica
set.

close(): Closes the connection, it doesn’t throw
any error even the connection is not opened or
already closed.

readyState: It is property of connection which holds state of the connection