Express

What is Express?
Express is a minimal and flexible Node.js web application framework that provides a robust set of features to develop web and mobile applications. It facilitates the rapid development of Node based Web applications.

Features of Express framework

• Allows to set up middlewares to respond to HTTP Requests.
• Defines a routing table which is used to perform different actions based on HTTP Method and URL.
• Allows to dynamically render HTML Pages based on passing arguments to templates.

Installing Express >   npm install express --save

You should install the following important modules along with express

• body-parser − This is a node.js middleware for handling JSON, Raw, Text and URL encoded form data.
• cookie-parser − Parse Cookie header and populate req.cookies with an object keyed by the cookie names.
• multer − This is a node.js middleware for handling multipart/form-data.

npm install body-parser –save
npm install cookie-parser –save
npm install multer --save

Heroku

What is Heroku?
Heroku is a container-based cloud Platform as a Service (PaaS). Developers use Heroku to deploy, manage, and scale modern apps. Our platform is elegant, flexible, and easy to use, offering developers the simplest path to getting their apps to market.

Heroku is fully managed, giving developers the freedom to focus on their core product without the distraction of maintaining servers, hardware, or infrastructure. The Heroku experience provides services, tools, workflows, and polyglot support—all designed to enhance developer productivity.

Install Heroku

• sudo add-apt-repository "deb https://cli-assets.heroku.com/branches/stable/apt ./"
• curl -L https://cli-assets.heroku.com/apt/release.key | sudo apt-key add -
• sudo apt-get update
• sudo apt-get install heroku

Check installation success by typing -> heroku --version

Deploy your application to Heroku

• git init
• git add .
• git commit -m "first commit"
• git status
• heroku login
• heroku create Name
• git push heroku master
• heroku open

AJAX

AJAX Introduction

• Update a web page without reloading the page
• Request data from a server - after the page has loaded
• Receive data from a server - after the page has loaded
• Send data to a server - in the background

What Is AJAX?

AJAX = Asynchronous JavaScript And XML.

AJAX is not a programming language.

AJAX just uses a combination of:

• A browser built-in XMLHttpRequest object (to request data from a web server)
• JavaScript and HTML DOM (to display or use the data)

AJAX is a misleading name. AJAX applications might use XML to transport data, but it is equally common to transport data as plain text or JSON text.

How AJAX Works

Simple Future Tense

Simple Future Tense is used to express an action that will occur or happen in the future. It is used to describe an action which will happen in near or far future after being said about it by the speaker.

Structure of Sentence

Main verb: Base or 1st form of the verb 

Auxiliary verbs: "will"

Positive of Sentences:

• Subject + Auxiliary verb + Main verb + Object
• Subject + Will + Base or 1st form of verb + Object

Examples:

1. He will come here tomorrow.
2. She will buy a laptop at the end of this month.
3. I will meet him in his office tomorrow.
4. They will send us a mail.
5. I will give him a nice gift.

Negative Sentences:

• Subject + Auxiliary verb + NOT + Main verb + Object
• Subject + Will + NOT + Base or 1st form of verb + Object

Examples:

1. He will not buy a car.
2. She will not come to college.
3. They will not play Cricket.
4. I will not go to university tomorrow.
5. You will not need any help.

Interrogative Sentences:

• Auxiliary verb + Subject + Main verb + Object
• Will + Subject + Base form of verb + Object

Examples:

1. Will they send him an invitation card?
2. Will she marry him?
3. Will they buy a new chair?
4. Will you help me?
5. Will you come here?

Past Perfect Tense

Past Perfect Tense is used to express two types of action which occurred or completed in the past. It is usually used to express an action which occurred a long time ago in past. It gives a sense of completion of an activity in past.

E.g: She had sent me her picture a year ago.

It may also be used to state an action that occurred in the recent past, but if it is intended to convey a sense of completion of the action with reference to other activities taken place after the same action.

E.g: The patient had died before the doctor came.

Structure of the Sentence :

 Main verb: Past Participle (3rd form of the verb) E.g:  gone, written
Auxiliary verbs: Had

Positive Sentences:

• Subject + Auxiliary verb + Main verb + Object
• Subject + Had + Past Participle (3rd form of the verb) + Object

Examples: 

1. She had undergone heart surgery in her childhood.
2. I had lost my camera.
3. They had shifted to a new home.
4. You had gone before I reached.
5. The patient had died before the doctor came.

Negative Sentences:

• Subject + Auxiliary verb + NOT + Main verb + Object
• Subject + Had + Not + Past Participle (3rd form of the verb) + Object

Examples:

1. He had not informed me about his illness.
2. She had not applied for some job.
3. I had not visited him.
4. You had not helped him when he needed your help.
5. We had not finished our work when he came here. 

Interrogative Sentences:

• Auxiliary verb + Subject + Main verb + Object
• Had + Subject + Past Participle + Object

Examples:

1. Had you completed your task?
2. Had he prepared himself for the exam?
3. Had she prepared some food for the kids?
4. Had I thought about my future?
5. Has he appeared in the exam?

Past Perfect Continous Tense

Past Perfect Progressive tense is used to describe an ongoing action that started in past and continued for some time in past. It expresses the continued nature of an action that started and stopped at some point in the past. The sentence includes a 'time-reference' to show that when the action started in past or for how long the action was continued in past.

For time-reference of the action, two specific words 'since' and 'for' are used in the sentence. The word 'since' is used if the exact starting time of the action is known or intended to be shown in the sentence. The word 'for' is used to express the amount of time for which the action was continued.

Structure of the Sentence:
Main verb: Present Participle (base form verb+ing)
Auxiliary verbs: Had Been

Positive Sentences:

• Subject + Auxiliary verb + Main verb + Object + Time-reference
• Subject + Had been + Present Participle (base form of verb + ing) + Object + Time_reference

Examples:

1. She had been watching the movie for two hours.
2. They were playing football since 10 O'clock.
3. He had been working for a Newspaper for five years.
4. I had been applying for jobs since December 2-12.
5. She had been waiting for you since Wednesday.

Negative Sentences:

• Subject + Auxiliary verb + Main verb + Object + Time-reference
• Subject + Had not been + Present Participle + Object + Time_reference

Examples:

1. They had not been doing their work since 2003.
2. He had not been drinking milk for five months.
3. She had not been trying to get a job since 2002.
4. I had not been listening to music since Thursday.
5. He had not been playing chess since 3 O'clock?

Interrogative Sentences:

• Had + Subject + Been + Present Participle + Object + Time-reference

Examples:

1. Had the kid been watching cartoon for eight days?
2. Had the baby been crying for one hour?
3. Had she been singing songs since 8 O'clock?
4. Had he been working in a hospital since 2001?
5. Had they been playing football for five hours?

Simple Past Tense

Simple Past Tense expresses an action that occurred in past. It expresses the following type past-actions:

• An action occurred just a little while ago

Examples : 

1. I ate an apple.
2. He caught a bird in the bushes.
3. I met a friend in the market.

• An action which occurred on a regular basis in past

Examples :

1. She worked in a factory.
2. The people paid less taxes in past.
3. The Ancients believed in superstitions.

Structure of the Sentence:

Main Verb: Past simple Form (2nd form of the verb)

Note. 2nd form of the verb is only used in a positive sentence. In negative and question sentence, 1st form of the verb is used as the main verb.

Auxiliary verb: Did

Positive sentence:

• Subject + Main verb + Object
• Subject + Past simple form (or 2nd form of verb) + object

Examples:

1. I bought a laptop.
2. He applied for a job.
3. I ate my meal.
4. They played the game properly.
5. You qualified for the exam.

Negative Sentences:

• Subject + Auxiliary verb + NOT + Main verb + Object
• Subject + Did + Not + Base form (1st form of verb) + Object

Examples:

1. She did not qualify her exam.
2. He did not find any job.
3. They did not buy a car.
4. You did not eat the food.
5. Kids did not like the movie.

Interrogative Sentences:

• Auxiliary verb + Subject + Main verb + Object
• Did + Subject + Base form (1st form of a verb) + Object

Examples:

1. Did you watch that movie?
2. Did she laugh?
3. Did I call you?
4. Did they shift to their new home?
5. Did he bring his document?

Present Perfect Continuous Tense

This tense express an action that started in past and continued to present or recently stopped. It is used to state an ongoing action that has started at a point in the past. A time reference is also used in the sentence to show that when the action started in past or for how long the action continued.

The specific words 'since' and 'for' are used in a sentence to show the time of action. The word 'Since' is used if the exact starting time of action is known or intended to be reflected in the sentence. The word 'for' is used to express the amount of time for which the action was continued.

Structure of the Sentence.

Main Verb: Present Participle (Base form + ing) E.g : going, eating
Auxiliary verb: Have been, Has been

Note :  If the subject of "she, he, it, or a singular noun", the auxiliary verb "has been" is used. If the subject of the sentence is "they, you, or a plural noun", the auxiliary verb "have been" is used.

Positive Sentences:

• Subject + Auxiliary verb + Main verb + Time-reference
• Subject + Have been / Has been + Present Participle (verb + ing) + Time-reference

Examples : 

1.  He has been living in New York since 1993.
2. She has been working in an organization since 2005.
3. He has been studying this book for three months. 
4. I have been watching the movie since 3 O'clock.
5. They have been teaching in this school for three years.

Negative Sentences:

• Subject + Auxiliary verb + Main verb + Time-reference
• Subject + Have not been / Has not been + Present Participle (verb + ing) + Time-reference

Examples:

1. He has not been working in factor since 2007.
2. She has not been studying her books for five days.
3. I have not been meeting him since 2012.
4. They have not been completing their work since Monday.
5. Kids have been not been playing games for five hours.

Interrogative Sentences:

• Has / Have + Subject + Been + Present Participle (verb + ing) + Time-reference

Examples: 

1. Have you been going to your college since 2013?
2. Has he been working as a teacher for three years?
3. Has she been writing the report since 7th August 2011?
4. Have they been making a noise for one hour?
5. Have I been wasting my time for three days?

Mongoose

What is Mongoose?

• Mongoose is an object modelling 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

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 the 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 the property of connection which holds the state of the connection.

Mongoose Schema

• constructor

syntax:-  Schema(definition, [options])
Example

• add ( )

syntax:-    add(obj,prefix)
Example

• get ( )

syntax:-  get(optionkey)
Example

• set ( )

syntax:-   set(key, [value]) 
Example

• index ( )

syntax:-  index(fields, [options], [options.expires=null])

Example 

• method ( )

syntax:-  method(methodname, function code)

Example 

• static ( )

syntax:-  static(method name,function def);

Example

• pre ( )
• post ( )

Mongoose model

• Constructor Model( )

syntax:-   Model(doc)

• save ( )

syntax:-  save([options], [options.safe], [options.validateBeforeSave], [fn])

Example

• find ()

Syntax:- find(conditions, [projection], [options], [callback])

• update ( )

Syntax:-  update(conditions, doc, [options], [callback])

Example 

• remove ( )

Syntax:-  remove(conditions, [callback])

Example 

ER Diagram

• 1976 proposed by Peter Chen

• An ER diagram is widely used in database design
• Represent the conceptual level of a database system
• Describe things and their relationships at a high level

Basic Concepts

• Entity set – an abstraction of similar things, 
• E.g:- cars, students
• An entity set contains many entities
• Entities are represented by means of rectangles. 
• Rectangles are named with the entity set they represent.
• E.g:- Teacher, Student, Project.

• Attributes: Common properties of the entities in an entity sets. Attributes are represented by means of ellipses. Every ellipse represents one attribute and is directly connected to its entity.

Attribute

• Composite VS Simple Attributes
• Single valued VS Multivalued Attributes
• Stored VS Derived Attributes
• Complex Attributes 

Relationship – specify the relations among entities from two or more entity sets

A relationship where two entities are participating is called a binary relationship. Cardinality is the number of instance of an entity from a relation that can be associated with the relation.

 One-to-one 

One-to-many

many-to-one

many-to-many

Keys

Key is an attribute or collection of attributes that uniquely identifies an entity among the entity set.

1.    Super Key − A set of attributes (one or more) that collectively identifies an entity in an entity set.

2.    Candidate Key − A minimal super key is called a candidate key. An entity set may have more than one candidate key.

3.    Primary Key − A primary key is one of the candidate keys chosen by the database designer to uniquely identify the entity set.