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Intro to ASP.NET Web Services

The World Wide Web

• A public client/server network
• Web browser
  • the client
  • makes HTTP "Requests"
• HTTP - Hypertext Transfer Protocol
  • protocols define communication rules
  • HTTP verbs and status codes
• Web server
  • serves files in a "Response"

2-tier or 3-tier architecture

• Data layer
• Business logic layer
  • Traditionally server languages
  • Java, C# (ASP.NET), Python, Ruby, PHP
• Presentation layer
  • Languages interpreted by the client
  • HTML, CSS, Javascript

Data layer - part of back-end

Relational database servers

• MS SQL, MySQL, Postgres SQL
• Data Relationships are defined and enforced by the database
• A "Company" table has a one-to-many relationship with an "Employees" table

Data layer - part of back-end

Non-relational database servers

• MongoDB, RavenDB
• Relationships (if any) are typically defined in the business logic layer
• Popular with "Big Data" applications - data can be stored in a less structured way

Data layer - part of back-end

Data can also be stored in structured "flat files"

• XML (Extensible Markup Language)
  • HTML is in fact XML that is interpreted by the browser
• CSV (comma-separated value) files
• JSON (Javascript Object Notation) files

Business logic layer

The web server

A typical full-page request:

• User clicks a link or types a URL
• Browser sends the HTTP Request for a web page

Business logic layer

The web server

• URL: Uniform Resource LocatorThe unique address of a file on the internet

Business logic layer

The web server

Business logic layer

The web server

A typical full-page response:

• Web server listens for incoming HTTP Requests
• Binds the subdomain and domain:
  • to a folder on the computer and retrieves a static HTML file from the file path of the URL
  • or to a web application running on the web server
• A "back-end" programming language performs logical operations:
  • Runs database queries to retrieve content data
  • Constructs the HTML file by combining tags and content data
• Returns the HTML file and dependency files in the HTTP Response

Business logic layer

A partial page load:

• An HTTP request comes in from a Javascript event handler
• This is called an "AJAX" request
• AJAX - Asynchronous Javascript and XML
• The HTTP Response returns information to the Javascript

HTTP and Object Data Wrappers

• Wrappers provide a way to "describe" an object as text.
• Sent in the HTTP Request or Response "payload"
• Wrapped text is then parsed into an object in memory
• SOAP-XML
• JSON (JavaScript Object Notation)

Web Services - what does Restful mean?

• REST (Representational state transfer) is a web service "architectural style"
• A RESTful web service API:
  • Uses "domain" objects (think of nouns)
  • i.e. Calendar, Event
  • Uses HTTP verbs for the actions
  • i.e. GET, POST, PUT, DELETE

ASP.NET Web Services Technologies

• Web Services
  • myService.asmx
• WCF Services
  • Windows Communication Foundation
  • myService.svc
• ASP.Net Web API

ASP.NET Web API

• ASP.NET 4 or higher (particularly MVC)
• Only transfers messages over HTTP protocol
• Microsoft intends this to be the HTTP services standard for ASP.NET going forward
• Resources:
  • Video: http://pluralsight.com/training/Courses/TableOfContents/aspnetwebapi
  • http://weblogs.asp.net/scottgu/archive/2012/02/23/asp-net-web-api-part-1.aspx

Web Clients

• Clients are not always browsers
• Applications that run on a web server can act as a client and call web service APIs on another web server.
• For example:
  • FitBit APIs: https://wiki.fitbit.com/display/API/API+Client+Libraries

Microsoft's Web Platform Installer

In a web browser, enter the URL to download Microsoft's Web Platform Installer, http://www.microsoft.com/web/downloads/platform.aspx

• Search for "Visual Studio Express 2013 for Web"
• Select "Visual Studio Express 2013 for Web with Microsoft Azure SDK - 2.4" released on 8/4/2014
• Click Install

Installation of Fiddler 2

Fiddler 2 will allow us to call our API, and view the raw HTTP Request and raw HTTP Response, before we build our client application.

• Installer will download automatically
• http://www.telerik.com/download/fiddler/fiddler2
• Double-click the installer to install

Web Service API - Project Setup

• Launch "VS Express 2013 for Web"
• Select "New Project..."
• "Empty" vs. "Single Page Application" templates
• "Single Page Application" installs a skeleton SPA built on Knockout.js. It supports login using a membership database or external authentication provider.

Web Service API - Project Setup

• Select "Empty" template and check off "Web API"
• Uncheck "Host in the Cloud"
• If interested, more about Azure cloud hosting:
  • http://azure.microsoft.com/en-us/develop/net/

Visual Studio Express Overview

• Left-side:
  • Text Editor
  • Toolbox
• Right-side:
  • Solution Explorer
  • Server Explorer
• Solution file
• Project file - can be more than one
• web.config