Maximizing.ASP.dot.NET.Real.World.ObjectOriented.Development [Electronic resources] نسخه متنی

The AddWithValue() method of the ParameterCollection is new to v2.0 of .NET. If you're using a previous version, you can use the same syntax with the Add() method (though it has been marked as obsolete in v2.0). The v2.0 compiler will warn you if you use the obsolete Add() method.Chapter 2, "Classes: The Code Behind the Objects," an interface is little more than a signature that says what members a class must have. Listing 4.2 shows a little piece of our interface.

Listing 4.2. The IPopForumsData interface

C#

namespace PopForums.Data
{
public interface IPopForumsData
{
int CreateNewPost(int TopicID, DateTime PostTime, 
string Name, int PeopleID, string IP, 
bool FirstInTopic, string FullText, bool ShowSig);
...more member definitions
}
}

VB.NET

Namespace PopForums.Data
Public Interface IPopForumsData
Function CreateNewPost(TopicID As Integer, _
PostTime As DateTime, Name As String, _
PeopleID As Integer, IP As String, _
FirstInTopic As Boolean, FullText As String, _
ShowSig As Boolean) As Integer
... more member definitions
End Interface
End Namespace

Our interface doesn't have any actual code in it. Its sole purpose is to let us know how our classes that implement it should look.

That's great, but our business rules classes are going to need to hit all these methods in our SqlClient class. To do this, we'll create a class that loads our data access class and caches it, according to values in our web.config file. A single static method called Methods() in the ClientLoader class will do this, as shown in Listing 4.3.

Listing 4.3. Loading our data access layer

C#

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namespace PopForums.Data
{
public class ClientLoader
{
public static IPopForumsData Methods()
{
Cache cache = HttpContext.Current.Cache;
if (cache["IPopForumsData"] == null)
{
if ((ConfigurationSettings.AppSettings["PopForumsDataClass"] == null) || 
(ConfigurationSettings.AppSettings["PopForumsDataDll"] == null))
// no data layer specified, use the internal one
cache.Insert("IPopForumsData", typeof(PopForums.Data.Provider).Module.Assembly
.GetType("PopForums.Data
SqlClient").GetConstructor(new Type[0]));
else
{
// user has specified an external data layer
string assemblyPath = "~\\bin\\" + ConfigurationSettings
.AppSettings["PopForumsDataDll"];
string className = ConfigurationSettings.AppSettings["PopForumsDataClass"];
cache.Insert("IPopForumsData", Assembly.LoadFrom(assemblyPath).GetType
(className).GetConstructor(new Type[0]));
}
}
return (IPopForumsData)(  ((ConstructorInfo)cache["IPopForumsData"]).Invoke(null) );
}
}
}

VB.NET

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Namespace PopForums.Data
Public Class ClientLoader
Public Shared Function Methods() As IPopForumsData
Dim cache As Cache = HttpContext.Current.Cache
If cache("IPopForumsData") Is Nothing Then
If ConfigurationSettings.AppSettings("PopForumsDataClass") Is Nothing Or
 ConfigurationSettings.AppSettings("PopForumsDataDll") Is Nothing Then
' no data layer specified, use the internal one
cache.Insert("IPopForumsData", GetType(PopForums.Data.Provider).Module
.Assembly.GetType("PopForums.Data.SqlClient").GetConstructor(New Type(0) {}))
Else
' user has specified an external data layer
Dim assemblyPath As String = "~\bin\" + ConfigurationSettings.AppSettings
("PopForumsDataDll")
Dim className As String = ConfigurationSettings.AppSettings
("PopForumsDataClass")
cache.Insert("IPopForumsData", [Assembly].LoadFrom(assemblyPath).GetType
(className).GetConstructor(New Type(0) {}))
End If
End If
Return CType(CType(cache("IPopForumsData"), ConstructorInfo).Invoke(Nothing),
 IPopForumsData)
End Function
End Class
End Namespace

The important thing to understand about the class in Listing 4.3 is that it loads an instance of the class we choose, which happens to implement IPopForumsData. If one isn't specified, it loads the default, our SqlClient class (for the purpose of this project, the SqlClient class is compiled in the same assembly as the rest of this code). The result is that we can call any method in our SqlClient class by creating an instance of it via the ClientLoader class and its Methods() method:

IPopForumsData data = PopForums.Data.ClientLoader.Methods();

As you can see, you can actually create an object whose type is an interface! Then you might see that we can call our CreateNewPost() method like this:

data.CreateNewPost( [parameters here] );

The IPopForumsData interface, the ClientLoader class, and the SqlClient class collectively make up our data access layer. This code is solely responsible for getting data in and out of the SQL Server database. To pipe the data in and out of another data store, we need only write a class that implements IPopForumsData and set values in our web.config file to load that class instead.

Now that we've found a way to isolate all our data access methods, we can create business rules. We'll create a class called Post and give it properties that match each of the fields in our database table. We'll also give it a constructor to create a new instance of a Post object, as well as methods to Create(), Update(), and Delete() data.

To add a new post entry to the database, we want our class to call the method from our data access layer and pass in the values as parameters. The Create() method of the Post class can perform any calculations, caching, or validation that we require and then execute the method from the data access layer, as in Listing 4.4.

Listing 4.4. The Create() method of the Post class

C#

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public int Create()
{
Cache cache = HttpContext.Current.Cache;
if (cache["pftopic" + _TopicID.ToString()] != null) cache.Remove("pftopic" + _TopicID
.ToString());
if (cache["pfpeopleposts" + _PeopleID.ToString()] != null) cache.Remove("pfpeopleposts"
 + _PeopleID.ToString());
IPopForumsData data = PopForums.Data.ClientLoader.Methods();
int postID = data.CreateNewPost(_TopicID,_PostTime,_Name,_PeopleID,_IP,_FirstInTopic
,_FullText,_ShowSig);
_PostID = postID;
Topic objTopic = new Topic(_TopicID);
objTopic.Update(); // this also calls the forum's update, which will refresh lastpostime
return postID;
}

VB.NET

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Dim cache As Cache = HttpContext.Current.Cache
If Not (cache(("pftopic" + _TopicID.ToString())) Is Nothing) Then
cache.Remove(("pftopic" + _TopicID.ToString()))
End If
If Not (cache(("pfpeopleposts" + _PeopleID.ToString())) Is Nothing) 
Then
cache.Remove(("pfpeopleposts" + _PeopleID.ToString()))
End If
Dim data As IPopForumsData = PopForums.Data.ClientLoader.Methods()
Dim postID As Integer = data.CreateNewPost(_TopicID, _PostTime, _Name, _PeopleID, _IP,
 _FirstInTopic, _FullText, _ShowSig)
_PostID = postID
Dim objTopic As New Topic(_TopicID)
objTopic.Update() ' this also calls the forum's update, which will refresh lastpostime
Return postID
End Function

This method does several things that fit squarely in the business rules layer of our application that we wouldn't want to leave to the user interface or the data access layer. You can see that it removes two cache entriesone that stores data on the parent topic and one that stores data on the user making the post. Those cached values are invalidated because the topic has changed, as well as information about the user with regards to the posts they've made. After that has been taken care of, it creates an instance of our data access class and calls the method to create a new post. The parameters that begin with an underscore are the private members of the class that correspond to properties, as we saw in Chapter 2 in Listing 2.7. Finally, the method creates a Topic object (another business rule class) and causes it to update its data, which forces the topic to calculate a new "last post" time.

It's not that critical that you understand all of those action items in the method, but it is important that you understand why they happen in this discrete business rules layer of the application. It isn't important to know how the data is stored or how the UI gets data into the class. Only the rules that deal with the data and how it's handled or calculated are important.

This gets us to what I call the user interface "glue." Despite having a great many declarative controls, ASP.NET still needs a bit of code to make the user interface work with your business rules layer. This glue code can appear in any of three places: in the page itself in a <script> block, in a partial class (unofficially known as "code-beside"), or in a class that the page inherits (known as "code-behind," the default place for code in versions of Visual Studio prior to 2005). Where you put this code is a matter of preference, but if you put it in the .aspx page file, some people may consider this an application design fault because it doesn't create that separation many programmers require. I put this code in with the rest of the page for convenience and to make it accessible for people not using Visual Studio. Considering you can't change the .aspx page without impacting the code-behind, or vice-versa, I don't feel that this separation is entirely necessary.

Partial classes are new as of v2.0 of .NET. In ASP.NET, they're merged on first-run with pages to form one complete class. We'll go into more detail in Chapter 6, "The Nuts and Bolts of IIS and Web Application."