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The BusinessBase(Of T) class exposes most of the functionality for a single editable object and combines support for data binding, validation rules, authorization rules, and n-level undo. I discuss each of these feature areas in s 7 through 16. Like all base classes, this class must be Serializable and MustInherit. Much of its behavior flows from its base classes or from other objects it contains. Here is the declaration of the class: Namespace Csla <Serializable()> _ Public MustInherit Class BusinessBase(Of T As BusinessBase(Of T)) Inherits Core.BusinessBase Implements Core.ISavable End Class End Namespace The generic type T is constrained to be the type of business object being created, so a business class is declared like this: <Serializable()> _ Public Class CustomerEdit Inherits BusinessBase(Of CustomerEdit) End Class The BusinessBase(Of T) class inherits from Csla.Core.BusinessBase, where most of the implementation resides. The reason for this is that BusinessBase(Of T) is generic and thus doesn t support polymorphism. The BusinessBase base class is not generic and so provides a common base class for all editable objects that is polymorphic: <Serializable()> _ Public MustInherit Class BusinessBase Inherits Csla.Core.UndoableBase Implements IEditableBusinessObject Implements System.ComponentModel.IEditableObject Implements System.ComponentModel.IDataErrorInfo Implements ICloneable Implements Csla.Security.IAuthorizeReadWrite Implements IParent Implements Server.IDataPortalTarget Implements IManageProperties End Class

<Serializable()> _ Public Class Customer Public Function Deserialize(ByVal state As Byte()) As Customer Using buffer As New MemoryStream(state) Dim formatter As BinaryFormatter = New BinaryFormatter() Return DirectCast(formatter.Deserialize(buffer), Customer) End Using End Function End Class Notice that this function returns a new customer object. It doesn t restore the existing object s state; it creates a new object. Somehow, you would have to tell any and all code that has a reference to the existing object to use this new object. In some cases, that might be easy to do, but it isn t always trivial. In complex applications, it s hard to guarantee that other code elsewhere in the application doesn t have a reference to the original object, and if you don t somehow get that code to update its reference to this new object, it will continue to use the old one. What s needed is some way to restore the object s state in place, so that all references to the current object remain valid but the object s state is restored. This is the purpose of the UndoableBase class.

Even if you use PrepareMethod, PrepareDelegate, and PrepareConstrainedRegions, allocation of memory on the managed heap can still cause an OutOfMemoryException There is not that much that the runtime can do to prevent an OutOfMemoryException from being thrown..

The BusinessBase class inherits from UndoableBase and thereby gains n-level undo capabilities Because all business objects inherit from BusinessBase, they too gain n-level undo Ultimately, the n-level undo capabilities are exposed to the business object and to UI developers via three methods: BeginEdit() tells the object to take a snapshot of its current state, in preparation for being edited Each time BeginEdit() is called, a new snapshot is taken, allowing the state of the object to be trapped at various points during its life The snapshot will be kept in memory so the data can be easily restored to the object if CancelEdit() is called CancelEdit() tells the object to restore the object to the most recent snapshot This effectively performs an undo operation, reversing one level of changes If CancelEdit() is called the same number of times as BeginEdit(), the object will be restored to its original state.

ApplyEdit() tells the object to discard the most recent snapshot, leaving the object s current state untouched It accepts the most recent changes to the object If ApplyEdit() is called the same number of times as BeginEdit(), all the snapshots will be discarded, essentially making any changes to the object s state permanent Sequences of BeginEdit(), CancelEdit(), and ApplyEdit() calls can be combined to respond to the user s actions within a complex Windows Forms UI Alternatively, you can totally ignore these methods, taking no snapshots of the object s state In such a case, the object will incur no overhead from n-level undo, but it also won t have the ability to undo changes This is common in web applications in which the user has no option to cancel changes Instead, the user simply navigates away to perform some other action or view some other data The CslaCore.

It is the programmer s responsibility to prevent memory allocations in CERs. Several operations are explicitly forbidden in CERs. These operations include the following: Usage of gcnew, because it results in newobj and newarr IL instructions. Boxing. Acquiring a CLR-specific object-based thread lock via Monitor.Enter or msclr::lock. Entering such a lock can result in a new lock structure being allocated. CAS checks. Calling .NET objects via special proxy objects called transparent proxies. In the current release of the CLR and the C++/CLI language, these constraints are nothing more than guidelines. Neither the runtime nor the compilers check whether a method is actually implemented according to the CER restrictions or not.

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