Entity Framework, generic way to track changes to an entity including navigation properties?

Question

I've seen all the questions out there for tracking changes to an entity, but none of those solutions included navigation properties. Is this even possible? I don't need some SUPER generic solution that just logs everything. I only want things tracked for specific "main" entities. And the audit log is going to be a human readable custom one, so not just some table that has oldData newData like I have seen in the examples on here.

I've gotten it almost to a good point except tracking the navigation properties, I have an Interface on the POCO's service that determines whether I want to track changes, then in my entityService.Save method I have this check:

var trackChangesService = this as ITrackChangesService<TClass>;
if (trackChangesService != null)
{
      TClass oldEntity = Repository.GetOldEntity(entity);
      trackChangesService.SaveChanges(entity, oldEntity);
}

The save changes method is what the ITrackChanges interface exposes and will have custom logic on a per entity basis (this includes email notifications, etc.), but the problem is I can't propertly get the oldEntity. Currently the method looks like this:

public TClass GetOldEntity(TClass entity)
    {
        //DbEntityEntry<TClass> oldEntry = Context.Entry(entity);
        ////oldEntry.CurrentValues.SetValues(oldEntry.OriginalValues);
        //var values = oldEntry.OriginalValues;
        //return (TClass)oldEntry.GetDatabaseValues().ToObject();

        return Context.Set<TClass>().AsNoTracking().FirstOrDefault(x => x.Id == entity.Id);
    }

You can see the code I have been playing with. I can get the regular properties old and new values fine, but the navigation properties do not carry over. But I need this information, say for instance I am editing a user and on the edit user screen, groups can be removed and added. When the save button is clicked, it performs those updates.

So my update view look like this:

private UserSaveModel Update(Guid id, UserSaveModel userSaveModel)
    {
        User user = _userService.GetOne(x => x.Id == id);
        user = _userService.ConvertFromSaveModel(userSaveModel, user);

        _userService.Save(user);

        return userSaveModel;
    }

I guess one way to look at the problem is, I am adjusting the values on the entity on the context in .ConvertFromSaveeModel() on the existing user record, including the navigation properties, so once I call save, that old navigation property data is gone.

Is there anyway to get original navigation property information for an entity using this workflow? If not, how can I change the workflow to make this possible? If I don't query the user object at the beginning and instead make one from scratch, some data that may not be exposed in the viewModel won't pass over, so I am not sure that will work. Any other suggestions? Maybe clone the entity and use that as original before I made changes? Does that carry over navigation properties?

Answer 1

Unfortunately, there is no easy way to detect Navigation Properties changes on EF SaveChanges, specially for the EF 7 (Core) version. Check this and this MSDN article.

So, if you don't have a relationship entity, and your entities are related like this:

public class User
{
    [Key]
    public int UserId { get; set; }
    public ICollection<Department> Departments { get; set; }
}

public class Department
{
    [Key]
    public int DepartmentId { get; set; }
    public ICollection<User> Users { get; set; }
}

and you only change a Navigation Property, say for example you add a Department to a User, like this:

using (var ctx = new MyContext())
{
    var user1 = ctx.Users.Include(u => u.Departments).First(u => u.Id == 1);
    var dept3 = ctx.Departments.First(d => d.Id == 3);

    user1.Departments.Add(dept3);

    ctx.SaveChanges();
}

The library Audit.EntityFramework will not detect the change, since you did a Relationship change, but not an Entity change.

You can avoid this problem creating an entity for your relation, i.e. a UserDepartment class. So you will see the changes to the relation as changes to that entity.

So far, this is the only way I found to obtain the relationship changes in case you don't have the relation entity. But... Only works for EF 6 so I didn't included that on my library.

Another workaround is to make sure to change another property value of the entity (i.e. a LastUpdatedDate column), or to explicitly mark the entity as Modified before the SaveChanges, so the library can detect the change and, at least, you'll see the entity current navigation properties.

For example:

using (var ctx = new MyContext())
{
    var user1 = ctx.Users.Include(u => u.Departments).First(u => u.Id == 1);
    var dept3 = ctx.Departments.First(d => d.Id == 3);
    user1.Departments.Add(dept3);
    ctx.Entry(user1).State = EntityState.Modified; // <-- Here
    ctx.SaveChanges();
}

Now the library will detect the change, and it will include some data about the change.

This is how the output (as JSON) would be like:

{
    "EventType": "MyContext",
    //...
    "EntityFrameworkEvent": {
        "Database": "Users",
        "Entries": [{
            "Table": "User",
            "Action": "Update",
            "PrimaryKey": {
                "UserId": 1
            },
            "Entity": {
                "UserId": 1,
                "Username": "federico",
                "Departments": [{
                    "DepartmentId": 3,
                    "DepartmentName": "Dept3",
                    "Users": []
                }]
            },
            "Changes": [],
            "ColumnValues": {
                "UserId": 1,
                "Username": "federico"
            },
            "Valid": true,
            "ValidationResults": []
        }],
        "Result": 1,
        "Success": true
    }
}

You need your context to inherits from AuditDbContext and set the IncludeEntityObjects to true:

[AuditDbContext(IncludeEntityObjects = true)]
public class MyContext : AuditDbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Department> Departments { get; set; }
}

I know this is not a solution for your problem, but it could probably help.