Creating an e:commerce Application with ASP'NET

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Creating an ecommerce Application with ASP.NET
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After working through the first Tutorial

• You should have created a basic ecommerce site
  with the
• following functionality
• A User and Log On system
• A Simple Search Page
• A Page Displaying Choices
• A Page for making Payments
• Website Administration Pages for Site Security

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Useful Video Tutorials
These tutorials can be found here
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More Video Tutorials
These tutorials can be found here
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A Few Words about OOP

• We have developed programs in
• JavaScript
• Visual Basic
• PHP
• Without using Object Oriented Programming
• Techniques

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What is Object Oriented Programming?
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Program Variables

• A program variable is a named area of computer
  memory used to store data

Think of a variable as a box in which data is
stored
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Program Variables
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Best Practice

• A webpage is used to supply data to program
  variables
• The program statements then process the data
  within the variables
• The results of the processing are then sent from
  the program variables to the webpage

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GUI, Variables Processing (1)
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GUI, Variables Processing (2)
The user Clicks the button and a copy of the data
is transferred to program variables
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GUI, Variables Processing (3)
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Arithmetic and Logic Unit (ALU)
Add
The ALU adds the content of two variables storing
the result in a third variable
Program variable
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GUI, Variables Processing (4)
Program variable
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The result of the addition is transferred from
the program variable to the GUI
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Tutorial Topics

• Creating a new project to add a class to
• Adding a class module to the project
• Adding class code to a module
• Writing code to create class instances
• Testing code in classes and in Sub Main

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Add the following statements to the Investment
class code
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Class methods

• A method to calculate the amount that will be
  returned given a specific set of investment
  parameters (Capital, PIR and Duration)
• A method to format and print the details of an
  investment

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Using the class in a short program
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Add new investment to my portfolio
Investor
Investment
n
Web Page
Investor
Investment
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What about Encapsulation?

• Stop users from
• Investing more than 1000 pounds
• Investing for more than 10 years
• Investing at interest rates greater than 5

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Public Properties
To protect attributes make them private
Now your programs cant see them
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Create Public Properties for each Attribute
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Now add the business rules
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Interesting Development

• Visual Studio encourages us to use the same
  programming language
• VB, C or whatever
• Whether we are developing windows applications,
  console applications or web applications.

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Why Bother with OOP?
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Northwind Tables
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A Closer Look at One Table
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A VB Front-End to Northwind DB

• Someone has developed a VB
• application to support this Use Case

Create an Invoice
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A VB Front-End to Northwind DB

• The Use Case involves the following
• three steps
• Take an order that's already been processed.
• Work out the value of everything in the order
• Print it out on a sheet of paper labelled invoice

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A VB form for the Use Case
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Possible Design Problems

• This form looks ok but the programmer has created
  some serious maintenance problems
• The problems relate to limitations of two-tier
  client server applications

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What problems?

• The behind-the-scenes code gets an order number,
  then goes out to the database (still implemented
  in Access), grabs the order information, and
  works out the financial details.

The code to do all of this is in the click event
of this button
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Another Use Case
Review Cash Flow
This allows the user to enter a couple of dates
and then get a complete list of all the
invoices/orders between those two dates.
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The Review Cash Flow Form
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Guess what?
All the code is in the click event for this button
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The Problem

• When you pull up an invoice in the Create Invoice
  form, the total is usually different from the one
  that appears in the Review Cashflow form.
• If only we had an Invoice class

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Invoice
Date etc
Calculate Total
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No Duplication of Logic!

• The code for calculating totals appears in one
  place only
• The click events on both buttons simply call up
  the Total method on the appropriate Invoice class
• So theyre bound to be consistent!

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Sensible Location for Business Logic

• Future programmers will look for an invoice class
  if they need to update the logic for calculating
  the total value of an invoice
• Just as they would look for a Customer table in
  the database if they had to change the way we
  store addresses.