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Looking at BusinessBase in Csla.Core, you can see that GetProperty() has many overloads, but ultimately does the following: protected P GetProperty<P>( PropertyInfo<P> propertyInfo, Security.NoAccessBehavior noAccess) { P result = default(P); if (CanReadProperty(propertyInfo.Name, noAccess == Csla.Security.NoAccessBehavior.ThrowException)) result = ReadProperty<P>(propertyInfo); else result = propertyInfo.DefaultValue; return result; }
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This technique is similar to the DependencyProperty concept that WPF and WF use.
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The method calls CanReadProperty(), which is part of the authorization rules subsystem I ll discuss in 10. That method checks to see if the current user is allowed to read this property. If the user is not authorized, the method will either throw an exception or return false, depending on the value of the noAccess parameter. Assuming no exception is thrown (which is the default), then either the value or a dummy default value will be returned. If the user is authorized to read the value, she gets the real value; otherwise, she gets a dummy value. The ReadProperty() method is used to get the real value if appropriate. ReadProperty() is a protected method of BusinessBase, so it s available in your business class as well. You should use GetProperty() when you want authorization rules to apply, and ReadProperty() when you want to read the property regardless of authorization rules. Normally, the UI disables the display of values that the user is not authorized to see, so even if a dummy value is returned here, the user will never see it. In fact, this is why the default behavior is to return a dummy value if the user isn t authorized to see the real value. Both Windows Forms and WPF data binding typically read the value, even if the control isn t visible to the user. If the property get throws an exception, then data binding will not work properly. Looking at the SetProperty() method in BusinessBase, you can see that it is even more complex: protected void SetProperty<P>( PropertyInfo<P> propertyInfo, P newValue, Security.NoAccessBehavior noAccess) { if (CanWriteProperty(propertyInfo.Name, noAccess == Security.NoAccessBehavior.ThrowException)) { try { P oldValue = default(P); var fieldData = FieldManager.GetFieldData(propertyInfo);
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if (fieldData == null) { oldValue = propertyInfo.DefaultValue; fieldData = FieldManager.LoadFieldData<P>(propertyInfo, oldValue); } else { var fd = fieldData as FieldManager.IFieldData<P>; if (fd != null) oldValue = fd.Value; else oldValue = (P)fieldData.Value; } LoadPropertyValue<P>(propertyInfo, oldValue, newValue, true); } catch (Exception ex) { throw new PropertyLoadException( string.Format(Properties.Resources.PropertyLoadException, propertyInfo.Name, ex.Message)); } } } While there s a lot of code here, the process flow can be distilled down to what you see in Figure 7-1.
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Figure 7-1. SetProperty() process flow The CanWriteProperty() method takes care of the authorization; I ll discuss this in 10. The LoadPropertyValue() method is a private helper method that takes care of actually setting the property value. It also does a lot of work, as shown in Figure 7-2.
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Figure 7-2. LoadPropertyValue() process flow The LoadProperty() method sets a property s value by ultimately calling LoadPropertyValue(). It is protected, and your business code can use it. You should use SetProperty() when you want to
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trigger authorization, business, and validation rules, and you should use LoadProperty() when you want to simply set a property value without triggering any of those behaviors. Table 7-1 lists the methods you can use to get and set property values in your business code.
Table 7-1. Methods That Get and Set Property Values
Method
GetProperty() ReadProperty() SetProperty() LoadProperty()
Description
Gets a property value after checking authorization Gets a property value without checking authorization Sets a property value after checking authorization, then triggers business and validation rules and data binding behaviors Sets a property value without checking authorization or triggering business or validation rules or data binding behaviors
Now that you have a high-level understanding of the way properties work, I ll dig into the specific options.
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