Getting original object from Entity Framework SaveChanges function? - vb.net

Question

For auditing reasons I am overriding the SaveChanges function. However, I want to capture to original and current values as the original object (i.e person) so that I can serialize both the before and after.
Public Overrides Function SaveChanges() As Integer
ChangeTracker.DetectChanges()
Dim ctx As ObjectContext = DirectCast(Me, IObjectContextAdapter).ObjectContext
Dim objectStateEntryList As List(Of ObjectStateEntry) = ctx.ObjectStateManager.
GetObjectStateEntries(EntityState.Added Or EntityState.Modified Or EntityState.Deleted).ToList()
For Each ent As ObjectStateEntry In objectStateEntryList
If Not ent.IsRelationship Then
Dim objectType As Type = ObjectContext.GetObjectType(ent.Entity.GetType)
Dim audit As New Audit With {
.ObjectId = ent.EntityKey.EntityKeyValues.First.Value,
.ObjectType = ObjectContext.GetObjectType(ent.Entity.GetType).Name,
.User = (From u In Users Where u.Username = My.User.Name).First
}
With audit
Select Case ent.State
Case EntityState.Added
.Action = "Created"
.Detail = "Record created"
Case EntityState.Deleted
.Action = "Deleted"
.Detail = "Record deleted"
Case EntityState.Modified
Dim newObj As String = SerializeToString(
Convert.ChangeType(ent.Entity, objectType)
)
.Action = "Modified"
.Detail = newObj.ToString
End Select
End With
End If
Next
Return MyBase.SaveChanges()
End Function
That's how far I got, but when I try and ChangeType it throws "Object must implement IConvertible".

Answer 1

The last time I worked on a project that absolutely needed to track every change, we used a history table and an ON UPDATE trigger. Changing data would fire the trigger, which would then copy the original row into the history table.
This is 100% EF compatible, but you need to set it up separately for each table.

Answer 2

This doesn't exactly answer your main question but may help you to improve your auditing.
Disclaimer: I'm the owner of the project Entity Framework Plus
I recommend you to look at our EF+ Audit Feature, all auditing information can be easily retrieved using this library.
// using Z.EntityFramework.Plus; // Don't forget to include this.
var ctx = new EntityContext();
// ... ctx changes ...
var audit = new Audit();
audit.CreatedBy = "ZZZ Projects"; // Optional
ctx.SaveChanges(audit);
// Access to all auditing information
var entries = audit.Entries;
foreach(var entry in entries)
{
foreach(var property in entry.Properties)
{
}
}
// CALL your serializer here
SerializeToString(entries, ...);
The code is Open Source.