How do I implement an audit trail using Entity Framework 5?

Question

I am trying to implement an audit trail in Entity Framework 5.

public class AuditZoneRepository : IAuditZoneRepository
    {
        private AISDbContext context = new AISDbContext();

        public int Save(AuditZone model, ModelStateDictionary modelState)
        {
            if (model.Id == 0)
            {
                context.AuditZones.Add(model);
            }
            else
            {
                var recordToUpdate = context.AuditZones.FirstOrDefault(x => x.Id == model.Id);
                if (recordToUpdate != null)
                {
                    recordToUpdate.Description = model.Description;
                    recordToUpdate.Valid = model.Valid;
                    recordToUpdate.ModifiedDate = DateTime.Now;
                }
            }

            try
            {
                context.SaveChanges();
                return 1;
            }
            catch (Exception ex)
            {
                modelState.AddModelError("", "Database error has occured.  Please try again later");
                return -1;
            }
        }
    }

To do so, I need the ObjectStateEntry for the entity :

entities.ObjectStateManager.GetObjectStateEntry(changedEntity);

as shown here .

When I try to add this to the save function it says unknown. What is the entities value in my case?

With Georges help I updated my save code as follows,

 public int Save(AuditZone model, ModelStateDictionary modelState)
        {
            if (model.Id == 0)
            {
                context.AuditZones.Add(model);
            }
            else
            {
                var recordToUpdate = context.AuditZones.FirstOrDefault(x => x.Id == model.Id);
                if (recordToUpdate != null)
                {
                    recordToUpdate.Description = model.Description;
                    recordToUpdate.Valid = model.Valid;
                    recordToUpdate.ModifiedDate = DateTime.Now;


                    var objectContext = ((IObjectContextAdapter)context).ObjectContext;

                    var entires = objectContext.ObjectStateManager.GetObjectStateEntry(recordToUpdate);

                    IEnumerable<string> modifiedProperties = entires.GetModifiedProperties();
                }
            }

            try
            {




                context.SaveChanges();
                return 1;
            }
            catch (Exception ex)
            {
                modelState.AddModelError("", "Database error has occured.  Please try again later");
                return -1;
            }
        }

but when I debug it the modifiedProperties has no results in it? am I putting this code in the wrong place?

Answer 1

Taken from the link you've posted:

"we have to use the ObjectStateManager on ObjectContext."

So, entities should be an implementation of ObjectContext .

To convert DbContext to ObjectContext use:

var objectContext = ((IObjectContextAdapter)dbContext).ObjectContext;

To get entries use:

var entires = objectContext.ObjectStateManager
                           .GetObjectStateEntries(EntityState.Unchanged);

More about the ObjectContext and its relation with DbContext :

• Entity Framework 4.1 and OriginalValues/CurrentValues and DbContext

• entity framework 4.1 objectContext vs dbContext

• What's the difference between DbContext and ObjectContext