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CHAPTER 3 s BUSINESS FRAMEWORK IMPLEMENTATION
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Private mRules As Dictionary(Of String, RolesForProperty) Private ReadOnly Property Rules() _ As Dictionary(Of String, RolesForProperty) Get If mRules Is Nothing Then mRules = New Dictionary(Of String, RolesForProperty) End If Return mRules End Get End Property Each entry in the dictionary is indexed by the property name and contains a RolesForProperty object to manage the list of allowed and denied roles for the property.
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Following the idea of lazy object creation, the GetRolesForProperty() method returns the list of roles for a property, creating it if it doesn t exist: Private Function GetRolesForProperty( _ ByVal propertyName As String) As RolesForProperty Dim currentRoles As RolesForProperty = Nothing If Not Rules.ContainsKey(propertyName) Then currentRoles = New RolesForProperty Rules.Add(propertyName, currentRoles) Else currentRoles = Rules.Item(propertyName) End If Return currentRoles End Function This method is scoped as Private because it is only used by other methods in the class. There is a public overload of GetRolesForProperty() that returns the list of roles for the property for a specific type of access (read, write and allow, deny): <EditorBrowsable(EditorBrowsableState.Advanced)> _ Public Function GetRolesForProperty(ByVal propertyName As String, _ ByVal access As AccessType) As String() Dim currentRoles As RolesForProperty = GetRolesForProperty(propertyName) Select Case access Case AccessType.ReadAllowed Return currentRoles.ReadAllowed.ToArray Case AccessType.ReadDenied Return currentRoles.ReadDenied.ToArray Case AccessType.WriteAllowed Return currentRoles.WriteAllowed.ToArray Case AccessType.WriteDenied Return currentRoles.WriteDenied.ToArray End Select Return Nothing End Function This method may be used by business developers if they need access to the list of roles perhaps to implement some type of custom authorization for a specific object. It is implemented
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here for flexibility not because the framework needs the functionality directly and so the <EditorBrowsable()> attribute is used to designate this as an advanced method.
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Associating Roles with Properties
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Of course, the business object needs to be able to associate lists of roles with its properties. The AuthorizationRules object exposes a set of methods for this purpose one for each access type. For instance, the AllowRead() method adds roles to the list of roles allowed to read a specific property: Public Sub AllowRead( _ ByVal propertyName As String, ByVal ParamArray roles() As String) Dim currentRoles As RolesForProperty = GetRolesForProperty(propertyName) For Each item As String In roles currentRoles.ReadAllowed.Add(item) Next End Sub This method accepts the name of the property and an array of role names. It uses the GetRolesForProperty() method to retrieve the appropriate RolesForProperty object from the dictionary, and then appends the roles to the ReadAllowed list. The DenyRead(), AllowWrite(), and DenyWrite() methods work in a similar fashion.
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The final behavior implemented by AuthorizationRules is to allow a business object to authorize the current user to read or write to a property. The Csla.Core.BusinessBase class implemented the actual algorithm for this purpose, but AuthorizationRules provides methods to make that possible.
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s Remember that the methods in BusinessBase were Overridable, so a business developer could Tip implement their own authorization algorithm by using AuthorizationRules if the algorithm in BusinessBase is inadequate.
For each access type, there are two methods. One indicates where there are any roles associated with the property for the specific access type, and the other checks the current user s roles against the roles for the property. For the read-allowed access type, the following methods are implemented: Public Function HasReadAllowedRoles( _ ByVal propertyName As String) As Boolean Return (GetRolesForProperty(propertyName).ReadAllowed.Count > 0) End Function Public Function IsReadAllowed(ByVal propertyName As String) As Boolean Return GetRolesForProperty(propertyName). _ IsReadAllowed(ApplicationContext.User) End Function The HasReadAllowedRoles() method returns True if there are any roles explicitly allowing read access to the specified property. Recall that the CanReadProperty() method in BusinessBase uses this method to decide how to apply authorization rules.
CHAPTER 3 s BUSINESS FRAMEWORK IMPLEMENTATION
s Note
The principal object is retrieved from Csla.ApplicationContext. This class is discussed in 4. Its User property returns the proper principal object in both ASP.NET and other environments, and should be used rather than System.Threading.Thread.CurrentPrincipal or HttpContext.Current.User.
The IsReadAllowed() method retrieves the IPrincipal object for the current user and collaborates with the underlying RolesForProperty object to determine if the user has a role that matches any of the roles in the list of roles that can read the specified property. The deny-read, allow-write, and deny-write access types each have a pair of methods implemented in a similar manner. Combined, these methods provide the tools needed by BusinessBase to implement the CanReadProperty() and CanWriteProperty() methods. This concludes not only the Csla.Security discussion, but all the supporting classes required for the main base classes in the Csla namespace itself. The rest of the chapter will cover the base classes typically used by business developers when creating their own editable and read-only business objects.
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