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CHAPTER 8 USING THE ASP.NET AJAX CONTROL TOOLKIT (PART 2)

@XmlRootElement(name = "helloWorld", namespace = "http://revealed.zukowski.net/") @XmlAccessorType(XmlAccessType.FIELD) @XmlType(name = "helloWorld", namespace = "http://revealed.zukowski.net/") public class HelloWorld { }

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Second, make careful note of the fact that only the public, read-write properties and public fields are exposed. Non-public properties aren t exposed. Read-only properties (such as Id on the Project and Resource objects) aren t exposed. This is because the Web Services implementation in ASP .NET relies on the XmlSerializer object to convert objects into and out of XML, and the XmlSerializer has limitations on what it will and won t serialize. Unless you re willing to compromise your object model s design specifically to accommodate the requirements of web service design, you won t be able to expose the data you choose via Web Services. Beyond this, Web Services requires that objects to be converted to and from XML expose a public default constructor. If the class doesn t provide a public default constructor, you ll get a runtime exception when attempting to access the web service. The design of CSLA .NET business objects specifically precludes the use of public default constructors, as they always use static factory methods to create instances of the business objects. Due to these drawbacks, directly exposing the business objects isn t a good practice. The answer instead is to create a facade around the business objects that can separate the public interface of the web service from the interface of the business objects. This facade can be constructed so that its properties and fields are always available for serialization into XML.

These additional steps provide a dramatic boost to scalability, but again at the cost of performance. The user s request now has two network hops, potentially resulting in double the network latency and contention. For a single user, the system gets slower; however, it is able to handle many times more users with acceptable performance levels. In the end, the application is constrained by the most limiting resource. This is typically the speed of transferring data across the network but if the database or application server is underpowered, it can become so slow that data transfer across the network won t be an issue. Likewise, if the application does extremely intense calculations and the client machines are slow, then the cost of transferring the data across the network to a relatively idle high-speed server can make sense.

The UI layer can interact directly with the objects in the Business Logic layer, thereby relying on them to perform all validation, manipulation, and other processing of the data. Likewise, the Data Access layer can interact with the objects as the data is retrieved or stored. If all the layers are running on a single machine (such as a smart client), then these parts will run in a single process and interact with each other with no network or cross-processing overhead. In more distributed physical configurations, the Business Logic layer will run on both the client and the application server, as shown in Figure 1-18.

Most applications will have some editable child objects, or even grandchild objects. Examples of these include the ProjectResource and ResourceAssignment objects. In many cases, the child objects are contained within a child collection object, which I ll discuss later. In other cases, the child object might be referenced directly by the parent object. Either way, the basic structure of a child object is the same; in some ways, this template is very similar to the editable root: <Serializable()> _ Public Class EditableChild Inherits BusinessBase(Of EditableChild) #Region " Business Methods " ' TODO: add your own fields, properties and methods Private mId As Integer Public Property Id() As Integer Get CanReadProperty(True) Return mId End Get Set(ByVal value As Integer) CanWriteProperty(True) If mId <> value Then mId = value PropertyHasChanged() End If End Set End Property Protected Overrides Function GetIdValue() As Object Return mId End Function #End Region #Region " Validation Rules " Protected Overrides Sub AddBusinessRules() ' TODO: add validation rules 'ValidationRules.AddRule(Nothing, "") End Sub #End Region #Region " Authorization Rules " Protected Overrides Sub AddAuthorizationRules() ' TODO: add authorization rules 'AuthorizationRules.AllowWrite("", "") End Sub #End Region #Region " Factory Methods "