Implementing Audit Log / Change History with MVC & Entity Framework

Question

I am building in a Change History / Audit Log to my MVC app which is using the Entity Framework.

So specifically in the edit method public ActionResult Edit(ViewModel vm), we find the object we are trying to update, and then use TryUpdateModel(object) to transpose the values from the form on to the object that we are trying to update.

I want to log a change when any field of that object changes. So basically what I need is a copy of the object before it is edited and then compare it after the TryUpdateModel(object) has done its work. i.e.

[HttpPost]
public ActionResult Edit(ViewModel vm)
{
    //Need to take the copy here
    var object = EntityFramework.Object.Single(x=>x.ID = vm.ID);

    if (ModelState.IsValid)
    {
        //Form the un edited view model
        var uneditedVM = BuildViewModel(vm.ID); //this line seems to confuse the EntityFramework (BuildViewModel() is used to build the model when originally displaying the form)
        //Compare with old view model
        WriteChanges(uneditedVM, vm);
        ...
        TryUpdateModel(object);
    }
    ...
}

But the problem is when the code retrieves the "unedited vm", this is causing some unexpected changes in the EntityFramework - so that TryUpdateModel(object); throws an UpdateException.

So the question is - in this situation - how do I create a copy of the object outside of EntityFramework to compare for change/audit history, so that it does not affect or change the EntityFramework at all

edit: Do not want to use triggers. Need to log the username who did it.

edit1: Using EFv4, not too sure how to go about overriding SaveChanges() but it may be an option

---

This route seems to be going nowhere, for such a simple requirement! I finally got it to override properly, but now I get an exception with that code:

public partial class Entities
{
    public override int SaveChanges(SaveOptions options)
    {
        DetectChanges();
        var modifiedEntities = ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
        foreach (var entry in modifiedEntities)
        {
            var modifiedProps = ObjectStateManager.GetObjectStateEntry(entry).GetModifiedProperties(); //This line throws exception The ObjectStateManager does not contain an ObjectStateEntry with a reference to an object of type 'System.Data.Objects.EntityEntry'.
            var currentValues = ObjectStateManager.GetObjectStateEntry(entry).CurrentValues;
            foreach (var propName in modifiedProps)
            {
                var newValue = currentValues[propName];
                //log changes
            }
        }

        //return base.SaveChanges();
        return base.SaveChanges(options);
    }
}

Answer 1

IF you are using EF 4 you can subscribe to the SavingChanges event.

Since Entities is a partial class you can add additional functionality in a separate file. So create a new file named Entities and there implement the partial method OnContextCreated to hook up the event

public partial class Entities
{
    partial void OnContextCreated()
    {
        SavingChanges += OnSavingChanges;
    }

    void OnSavingChanges(object sender, EventArgs e)
    {

        var modifiedEntities = ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
        foreach (var entry in modifiedEntities)
        {
            var modifiedProps = ObjectStateManager.GetObjectStateEntry(entry.EntityKey).GetModifiedProperties();
            var currentValues = ObjectStateManager.GetObjectStateEntry(entry.EntityKey).CurrentValues;
            foreach (var propName in modifiedProps)
            {
                var newValue = currentValues[propName];
                //log changes
            }
        }
    }
}

If you are using EF 4.1 you can go through this article to extract changes

Answer 2

See FrameLog, an Entity Framework logging library that I wrote for this purpose. It is open-source, including for commercial use.

I know that you would rather just see a code snippet showing how to do this, but to properly handle all the cases for logging, including relationship changes and many-to-many changes, the code gets quite large. Hopefully the library will be a good fit for your needs, but if not you can freely adapt the code.

FrameLog can log changes to all scalar and navigation properties, and also allows you to specify a subset that you are interested in logging.

Answer 3

There is an article with high rating here at the codeproject: Implementing Audit Trail using Entity Framework . It seems to do what you want. I have started to use this solution in a project. I first wrote triggers in T-SQL in the database but it was too hard to maintain them with changes in the object model happening all the time.