Question

I was wondering if anyone could offer some input for an implementation of audit logging for inserts. I need to ensure that it is transactional.

I have an audit DbSet built upon the following POCO:

public class Audit {
    public int Id { get; set; }
    public User User { get; set; }
    public DateTime Created { get; set; }
    public string Type { get; set; }
    public int EntityId { get; set; }
    public string Message { get; set; }
}

I have a DbSet, say Users, that when I do an insert I want to create automatically add an Audit entity in the Audit DbSet. Consider the following code:

//var user = new User();
//user.Created = DateTime.Now;
//user.Username = "testuser";
//user.Password = "testpassword";
//dataContext.Users.Add(user);

var post = new Post();
post.Created = DateTime.Now;
post.Title = "A sample post";
post.Published = true;
post.Body = "Some content goes in here...";

dataContext.Posts.Add(post);

var audit = new Audit();
audit.Created = DateTime.Now;
audit.User = CurrentUser.User; // Currently logged in user
audit.Type = "Post.Add";
audit.EntityId = post.Id;
audit.Message = "New post was created";

dataContext.Audits.Add(audit);

dataContext.SaveChanges();

In this instance, an audit entity will be added but the “EntityId” property will be set to 0 (default value) and not to the identity of the created user post, i.e. the identity value (SCOPE_IDENTITY()/@@IDENTITY).

I’d like to keep both points in a single transaction, rather than split the items into two transactions, i.e. persist the User Post first, then persist the Audit second as there is a chance the Audit may fail.

Answer 1

Override DbContext.SaveChanges() and look at all the ChangeTracker.Entries().Where(e=>e.State != EntityState.Unchanged).

Here is an example from a R&D project of mine:

public override int SaveChanges()
{
    int recordsUpdated = 0;

    var journalEntries = new List<AuditJournal>();

    foreach (var entry in this.ChangeTracker.Entries<ITrackedEntity>().Where(e=>e.State != EntityState.Unchanged))
    {
        AuditJournal journal = new AuditJournal();
        journal.Id = Guid.NewGuid();
        journal.EntityId = entry.Entity.Id.Value;
        journal.EntityType = entry.Entity.EntityType;
        journal.ActionType = entry.State.ToString();
        journal.OccurredOn = DateTime.UtcNow;
        //journal.UserId = CURRENT USER
        //journal.PreviousEntityData = XML SERIALIZATION OF ORIGINAL ENTITTY

        journalEntries.Add(journal);
    }

    using (var scope = new TransactionScope())
    {
        recordsUpdated = base.SaveChanges();

        foreach (var journalEntry in journalEntries)
            this.AuditJournal.Add(journalEntry);

        base.SaveChanges(); //Save journal entries

        scope.Complete();
    }

    return recordsUpdated;
}

//Every entity that needs to be audited has to implement this interface
public interface ITrackedEntity
{
    string EntityType { get; }
    Guid? Id { get; set; }
}