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token. Metadata tokens for entries in the metadata table for functions and methods have the pattern 0x06 . When an assembly is loaded, the CLR iterates through all .vtfixup entries of the assembly. For each .vtfixup entry, it creates a thunk to the target function dynamically and stores a pointer to that thunk in the interoperability vtable specified by the RVA of the .vtfixup entry.

At the beginning of Listing 8-16, the method attempts to retrieve an existing security context token from the global cache using a method called RetrieveSecurityContextTokenFromGlobalCache. Listing 8-17 provides the code listing for this method.

In the same way that IBusinessObject provides a form of polymorphism and commonality across all business objects, IReadOnlyObject does the same thing for read-only business objects specifically those that inherit from ReadOnlyBase<T>. It turns out that all read-only objects support a method for authorization: CanReadProperty(). This method is defined in the interface as follows: public interface IReadOnlyObject : IBusinessObject { bool CanReadProperty(string propertyName); } The CanReadProperty() method is discussed in 12 when I discuss authorization.

The options to enable inserting, editing (updating), and deleting are all driven by the properties discussed here. If CanInsert returns False, for instance, then the Enable Inserting option won t be visible to the business developer within Visual Studio. Both BusinessBase and BusinessListBase are used to create editable objects, thus automatically supporting delete, insert, and update operations. Recall that in 3 both these classes implement the Csla.Core.IEditableObject interface, making it easy to determine if the business object class is one of these types. For instance, the CanUpdate property looks like this: Public Overrides ReadOnly Property CanUpdate() As Boolean Get Dim objType As Type = CslaDataSource.GetType( _ mOwner.DataSourceControl.TypeAssemblyName, _ mOwner.DataSourceControl.TypeName) If GetType(Csla.Core.IUndoableObject).IsAssignableFrom(objType) Then Return True Else Return False End If End Get End Property The CanDelete and CanInsert properties are similar. The property calls a GetType() method on CslaDataSource to retrieve a Type object representing the type of the business object. Here s the code for that helper method in CslaDataSource:

When an object is new, it means that the object exists in memory but not in the database or other persistent store. If the object s data resides in the database, the object is considered to be old. I typically think of it this way: if the primary key value in the object corresponds to an existing primary key value in the database, the object is old; otherwise it is new. The value behind the IsNew property is stored in an _isNew field. When an object is first created, this value defaults to the object being new: private bool _isNew = true; The IsNew property simply exposes this value: [Browsable(false)] public bool IsNew { get { return _isNew; } } The property is adorned with the Browsable attribute from the System.ComponentModel namespace. This attribute tells data binding not to automatically bind this property. Without this attribute, data binding would automatically display this property in grids and on forms, and typically, this property shouldn t be displayed. This attribute is used on other properties in BusinessBase as well.

Figure 8-2. The connection strings used to access SQL Azure using ADO.NET, ODBC, or OLE DB You can easily create a new database by clicking the Create Database button in the management page. An example of the results of creating a custom database is shown in Figure 8-3.

Figure 11-12. Left alignment (DT_AlignmentLeft)

In the following code, Main starts execution and calls method A, which calls method B. A description and diagram of the process are given after the code and in Figure 11-9. class Program { static void Main() { MyClass MCls = new MyClass(); try { MCls.A(); } catch (DivideByZeroException e) { Console.WriteLine("catch clause in Main()"); } finally { Console.WriteLine("finally clause in Main()"); } Console.WriteLine("After try statement in Main."); Console.WriteLine(" -- Keep running."); } } class MyClass { public void A() { try { B(); } catch (System.NullReferenceException) { Console.WriteLine("catch clause in A()"); } finally { Console.WriteLine("finally clause in A()"); } } void B() { int x = 10, y = 0; try { x /= y; } catch (System.IndexOutOfRangeException) { Console.WriteLine("catch clause in B()"); } finally { Console.WriteLine("finally clause in B()"); } } }