s USING THE CSLA .NET BASE CLASSES in VB.NET

Encoding PDF 417 in VB.NET s USING THE CSLA .NET BASE CLASSES

The most common type of collection is one that is contained within a parent object to manage a collection of child objects for that parent; like ProjectResources and ResourceAssignments in the sample application.

s Note that the parent object here might be a root object, or it might be a child itself child objects can be Tip nested, if that s what the business object model requires. In other words, this concept supports not only root-child, but also child-grandchild and grandchild-to-great-grandchild relationships.

A child collection class inherits from BusinessListBase and calls MarkAsChild() during its creation process to indicate that it s operating in child mode. This also means that it won t be directly retrieved or updated by the DataPortal, but instead will be retrieved or updated by its parent object: <Serializable()> _ Public Class EditableChildList Inherits BusinessListBase(Of EditableChildList, EditableChild) #Region " Factory Methods " Friend Shared Function NewEditableChildList() As EditableChildList Return New EditableChildList End Function Friend Shared Function GetEditableChildList( _ ByVal dr As SqlDataReader) As EditableChildList Return New EditableChildList(dr) End Function Private Sub New() MarkAsChild() End Sub Private Sub New(ByVal dr As SqlDataReader) MarkAsChild() Fetch(dr) End Sub #End Region #Region " Data Access " Private Sub Fetch(ByVal dr As SqlDataReader) RaiseListChangedEvents = False While dr.Read Add(EditableChild.GetEditableChild(dr)) End While RaiseListChangedEvents = True End Sub Friend Sub Update(ByVal parent As Object)

RaiseListChangedEvents = False For Each item As EditableChild In DeletedList item.DeleteSelf() Next DeletedList.Clear() For Each item As EditableChild In Me If item.IsNew Then item.Insert(parent) Else item.Update(parent) End If Next RaiseListChangedEvents = True End Sub #End Region End Class As you can see, this code is very similar to a root collection in structure. The differences start with the factory methods. Since only a parent object can create or fetch an instance of this class, the Shared factory methods are scoped as Friend. The Shared method to create an object simply returns a new collection object. As with the EditableChild template, the constructor calls MarkAsChild() to indicate that this is a child object. Likewise, the Shared method to load the child collection with data creates a new collection object and then calls a parameterized constructor just like in the EditableChild template. That constructor calls a Fetch() method to load the data. The Update() method is identical to the DataPortal_Update() method in the EditableRootList. It loops through the list of deleted child objects, calling their DeleteSelf() methods, and then loops through the active child objects, calling Insert() or Update() as appropriate. Notice, however, that the Update() method accepts a reference to the parent object as a parameter, and this value is provided to the child objects Insert() and Update() methods. As discussed earlier, this allows the child objects to use data from the parent object as needed for things like foreign key values and so forth.

Sometimes, an application may need an object that provides data in a read-only fashion. For a readonly list of data, there s ReadOnlyListBase; but if the requirement is for a single object containing read-only data, it should inherit from ReadOnlyBase. This is one of the simplest types of object to create, since it does nothing more than retrieve and return data, as shown here: <Serializable()> _ Public Class ReadOnlyRoot Inherits ReadOnlyBase(Of ReadOnlyRoot) #Region " Business Methods " Private mId As Integer

Public ReadOnly Property Id() As Integer Get CanReadProperty(True) Return mId End Get End Property Protected Overrides Function GetIdValue() As Object Return mId End Function #End Region #Region " Authorization Rules " Protected Overrides Sub AddAuthorizationRules() ' TODO: add authorization rules 'AuthorizationRules.AllowRead("", "") End Sub Public Shared Function CanGetObject() As Boolean ' TODO: customize to check user role 'Return ApplicationContext.User.IsInRole("") Return True End Function #End Region #Region " Factory Methods " Public Shared Function GetReadOnlyRoot(ByVal id As Integer) As ReadOnlyRoot Return DataPortal.Create(Of ReadOnlyRoot)(New Criteria(id)) End Function Private Sub New() ' require use of factory methods End Sub #End Region #Region " Data Access " <Serializable()> _ Private Class Criteria Private mId As Integer Public ReadOnly Property Id() As Integer Get Return mId End Get End Property Public Sub New(ByVal id As Integer) mId = id End Sub End Class