Global.asax file in asp.net

Global.asax file in asp.net

The Global.asax file, also known as the ASP.NET application file, is an optional file that contains code for responding to application-level events raised by ASP.NET or by HttpModules. 

The Global.asax file is optional. If you do not define the file, the ASP.NET page framework assumes that you have not defined any application or session event handlers.

The Global.asax file itself is configured so that any direct URL request for it is automatically rejected; external users cannot download or view the code written within it.

There can be only one Global.asax file per application and it should be located in the application's root directory only.


The Global.asax contains two types of events those are
Events which are fired for every request
Events which are not fired for every request


Events which are fired for every request

Application_BeginRequest() – This event raised at the start of every request for the web application.

Application_AuthenticateRequest – This event rose just before the user credentials are authenticated. We can specify our own authentication logic here to provide custom authentication.

Application_AuthorizeRequest() – This event raised after successful completion of authentication with user’s credentials. This event is used to determine user permissions. You can use this method to give authorization rights to user. 

Application_ResolveRequestCache() – This event raised after completion of an authorization request and this event used in conjunction with output caching. With output caching, the rendered HTML of a page is reused without executing its code.

Application_AcquireRequestState() – This event raised just before session-specific data is retrieved for the client and is used to populate Session Collection for current request.

Application_PreRequestHandlerExecute() – This event called before the appropriate HTTP handler executes the request.

Application_PostRequestHandlerExecute() – This event called just after the request is handled by its appropriate HTTP handler.

Application_ReleaseRequestState() – This event raised when session specific information is about to serialized from the session collection.

Application_UpdateRequestCache() – This event raised just before information is added to output cache of the page.

Application_EndRequest() – This event raised at the end of each request right before the objects released. 

Now we will see

Events which are not fired for every request

Application_Start() – This event raised when the application starts up and application domain is created.

Session_Start() – This event raised for each time a new session begins, This is a good place to put code that is session-specific.

Application_Error() – This event raised whenever an unhandled exception occurs in the application. This provides an opportunity to implement generic application-wide error handling.

Session_End() – This event called when session of user ends.

Application_End() – This event raised just before when web application ends.

Application_Disposed() – This event fired after the web application is destroyed and this event is used to reclaim the memory it occupies.

Class, Object

Class
Class defines the attributes and behavior used by all instance of class.
for ex
Class name : Car
Attributes [Properties] : Color, Speed 
Behavior [Methods] : Accelerate, Turn and Brake

No memory is allocated when class is created.
Default access specifier for class is Private.
Class is a reference type, so when call the class by creating the object memory is allocated on the heap.

Object
An Object is an instance of class.
Object have individual copies of attributes and share a common set of behavior.
for ex


Class name : Car
Attributes [Properties] : Color, Speed 
Behavior [Methods] : Accelerate, Turn and Brake



Object is creating using new keyword.

Inheritance, Association, Aggregation, and Composition

Inheritance, Association, Aggregation, and Composition

      1.  Inheritance [IS a relationship]

      2.  Association [Using Relationship]

      3. Aggregation [ Has a Relationship]

      4. Composition -  [Part of relationship]

1.      Inheritance [ IS a relationship]

Example

Consider there are two Classes.

1.Employee

2.Manager 

Here Employee is the Parent class; Manager is the child class.Manager is one of the types of Employee. Class Manager is a relation with Class Employee.

I.e. Manager is (a or an) Employee

2. Association [Using relationship]

Example

       1. Manager

       2. SwipeCard

Here Manager and SwipeCard are two different classes.

Manager uses a swipe card to enter XYZ premises.

I.e. Manager Using swipe card to enter XYZ premises.

The above diagram shows how the SwipeCard class uses the Manager class and the Manager class uses the SwipeCard class. You can also see how we can create objects of the Manager class and SwipeCard class independently and they can have their own object life time.

This relationship is called the “Association” relationship.

3.      Aggregation [ Has a Relationship]

Aggregation gives us a 'has-a' relationship. Within aggregation, the lifetime of the part is not managed by the whole. 

The above UML describes Aggregation relation which mentions that Employee refers to Address. And life time of Address is not managed by Employee. It is like"Employee has a Address". Let us see how it can be implemented in C#.

So how do we express the concept of aggregation in C#? Well, it's a little different to composition. Consider the following code:

public class Address
{
 . . .
}

public class Person

{

     private Address address;

     public Person(Address address)

     {

         this.address = address;

     }

     . . .

}

Person would then be used as follows:

Address address = new Address ();
Person person = new Person(address);

    Or

Person person = new Person (new Address() );

4. Composition  -  [Part of relationship]

Composition gives us a 'part-of' relationship.

If we were going to model a car, it would make sense to say that an engine is part-of a car. Within composition, the lifetime of the part (Engine) is managed by the whole (Car), in other words, when Car is destroyed, Engine is destroyed along with it. So how do we express this in C#?

public class Engine
{
 . . . 
}

public class Car

{

    Engine e = new Engine();

    .......

}

As you can see in the example code above, Car manages the lifetime of Engine.