Audit with Entity Framework

Question

I am wanting to do the audit tables of my entities. At first I thought to overwrite the method SaveChanges. I also thought of writing a method that will be doing the audit on my repository base. Using both forms, I will have a single audit table for my entire system.

But for performance reasons I need each entity to have its log table.

What would be the best way to intercept the type of my entity so that I can save in the audit table of the same?

My code until then is like this:

public override int SaveChanges()
{
     var entriesAdicionadas = ChangeTracker.Entries().Where(e => e.State == EntityState.Added).ToList();

     var entriesModificadas = ChangeTracker.Entries().Where(e => e.State == EntityState.Modified).ToList();

     var entriesDeletadas = ChangeTracker.Entries().Where(e => e.State == EntityState.Deleted).ToList();
     foreach (var entry in entriesAdicionadas)
     {

     }
     int result = base.SaveChanges();

     foreach (var entry in entriesModificadas)
     {
         var nome = entry.Entity.GetType().Name;
     }

     base.SaveChanges();

     foreach (var entry in entriesDeletadas)
     {
         var nome = entry.Entity.GetType().Name;
     }

     return result;
} 

Answer 1

Implementation Caseira

First you need to create a way to relate the Model log with the Model that will be audited. This can be done by declaring a Model with generic. For example:

public class ModelDeLogGenerico<T>
    where T: class
{

}

T doesn’t have to be class. T can be an ancestral class of all its Models, or an interface. In some projects I do, all the Models derive from an interface called IEntityBase, in which I force the Model to have two more properties: on the first record the date the record was created and on the second the date it was last modified, which is more or less like this:

namespace MyProject.Models.Interfaces
{
    interface IEntityBase
    {
        DateTime LastModified { get; set; }
        DateTime CreatedOn { get; set; }
    }
}

This ensures that your Model Log cannot necessarily receive any class. The class to be valid needs to implement IEntityBase. My Log class, so it would look like this:

public class ModelDeLogGenerico<T>
    where T: IEntityBase
{

}

Suppose now a Model any of your system:

public class Fruta 
{
    ...
}

His respective log will be:

public class LogFruta<Fruta>
{
    ...
}

Having this, we can now identify that LogFruta audita Fruta. The following Reflection-based code searches the assembly of your application which class has as generic argument the class Fruta:

var log = Assembly.GetExecutingAssembly().GetTypes().FirstOrDefault(t => t.GetGenericArguments()[0] == entry.GetType());

Solutions Pronto

The Entityframework.Extended. has native ability to log for you. There’s an explanation here.