The eXpressApp Framework supplies the Audit Trail System for WinForms and ASP.NET applications. This system is intended to provide you information on changes that are being made to the application's persistent objects. For example, you can retrieve information on the kind of change (object is created, changed, etc.), who made this change, with what object, the previous and new property values, and so on. A change is registered between two sequential events of object saving to a data storage. To have this system in your application, you should use the Audit Trail module, which represents it. This topic explains the mechanisms for trailing object changes, and provides ways to customize them.
Currently, we do not to provide built-in support for Entity Framework (EF) in this module, because its implementation heavily depends on our XPO ORM, and we do not have a sufficient number of customer requests in this regard. If you use EF for data access in your XAF application and require a similar functionality for your project, feel free to contact us and describe your business requirements so we can provide you with alternative solutions. In general, you can integrate any custom or standard solution for Entity Framework, which you would implement to solve the same requirement in non-XAF applications. We will also continue monitoring user demand in this regard and it is possible that we will review our current decision in the future.
The AuditTrailModule is represented by the DevExpress.ExpressApp.AuditTrail.v19.1.dll assembly. To use the module in an application, add it to your application project or one of the application modules via the Application Designer or Module Designer, respectively. In addition, check that the DevExpress.Persistent.Base.v19.1.dll assembly is referenced in your application, since it contains XAF-independent services used by the Audit Trail module.
You can add modules to your application when you create a new XAF solution using the Solution Wizard. To do this, select modules in the Choose Extra Modules step.
After the necessary assemblies listed above have been referenced, all persistent objects in the application will be audited. In addition, their simple, reference and collection properties, which are persistent, will be audited as well. The changes made to these objects and their properties will be logged in the database.
The following table lists the changes which are logged by the Audit Trail module:
|ObjectCreated||The audited object has been created.|
|InitialValueAssigned||An initial value has been assigned to the audited object before the first save.|
|ObjectChanged||The audited object's property has been changed.|
|ObjectDeleted||The audited object has been deleted.|
|AddedToCollection||The audited object has been added to a collection.|
|RemovedFromCollection||The audited object has been removed from a collection.|
|CollectionObjectChanged||An object from the audited object has been changed.|
|AggregatedObjectChanged||The object aggregated by the audited object has been changed.|
|CustomData||Custom data has been added to the audit log.|
In code, changes are represented by the AuditDataItem class. This class' properties are logged. By default, they are saved to the database by an AuditDataStore object. This object creates an AuditDataItemPersistent persistent object and saves it to the database. To save changes represented by the AuditDataItem objects in another storage, inherit a custom class from the AuditDataStore class and override the Save method (see the Customize the Audit Trail System topic).
To analyze the audit log, you need to know what database tables represent it. With the Audit Trail module, the following tables are added to the database:
Represents the table where the AuditDataItemPersistent objects are stored. Each time one of the changes listed above is made, a new record is added to this table. The table's AuditedObject field contains references to the corresponding records in the AuditObjectWeakReference table. The OldObject and NewObject fields contain references to the corresponding records in the XPWeekReference table. These fields' string representations are stored into the OldValue and NewValue fields, respectively.
Contains data on the objects that have been changed. Object identifiers are stored as strings.
Contains data on both the objects that have been changed and the objects that have taken part in a change. Object identifiers are stored in the GuidId or IntId field, depending whether they are stored as Guid or integer values. So, the AuditedObjectWeakReference table represents a more convenient way to access object data than via the XPWeakReference table.
It is possible to lose some of the object changes, if these changes are performed within a session that is not audited. This can occur if you manually create a Session or UnitOfWork. To avoid such a failure, use the Application.CreateObjectSpace method, when you need to create your own Session or UnitOfWork:
Do not write a statement like the following: