Entity Framework - generic auditing by entity or table

Question

I need to audit data in some tables in my server database so my clients can take partial updates (by table/entity). Data in the server database is only edited from the server website.

The audits will be requested by a client: WHERE Id > [Clients Last Id] , the server will then do some processing and then return the latest audits to keep themselves up to date.

I can't seem to get to a generic pattern that will work across the board for all of my models:

public class Domain {
    public int Id { get; set; }
    public string Property1 { get; set; }
    public int Property2 { get; set; }
}

Then I think I want to be able to do something like so:

public class DomainContext : DbContext {
    public DbSet<Domain> Domain { get; set; }
    public DbSet<History<Domain>> DomainHistory { get; set; }
}

This is my problem class taking this route, I want to inherit from Domain so things like property changes and EF migrations (in code first) will 'just work'. But I Cannot derive from 'T' because it is a type parameter

public class History<T> 
    : T //Cannot derive from 'T' because it is a type parameter
    where T : class {
    public DateTime CreatedOn { get; set; }
    public int CreatedByUserId { get; set; }
    public int EntityFK { get; set; }
    // This will always be the current version
    //public T Entity { get; set; }

    // I could store a snapshot of the state at the time of the audit
    public string XMLData { get; set; }
}

I don't know if my use of generics is warranted here but I'm basically trying to get to a point where I can do the below so my models play nicely with EF Migrations:

        Domain d = GetDomainModel();
        History<Domain> dh = new History<Domain>();

        dh.Property1 = d.Property1;
        dh.Property2 = d.Property2;

How can this be done?

Answer 1

For a basic audit of your entities you can use a base class and intercept the changue type in a override of savechangues in context, like this (sorry of format, i write in mobile):

public class AuditBase
{
    //Adapt your requirements, the propertys are exists in db
    public datetime creationdate { get; set; }
    public datetime modificationdate { get; set; }
    public string creationuser { get; set; }
    public string modificationuser { get; set; }
}

public class ModelBBDD : AuditBase
{ }

You can override the SaveChanges method of Context. In the method, you can through the ChangueTracker property of Database Class for added or updates dto's, like this:

var dto = entity as auditbase;
if (dto == null) continue;
if (dto.state == entitystate.added)
{
    ((Auditbase)entity).creationdate = datetime.now;
    ((Auditbase)entity).creationuser = environment.username;
}
else if( dto.state == entitystate.modified)
...
...

If you can log all the changues of properties, you can trough all the properties of dto with reflection and type in SaveChanges, and save values in log.