Entity Framework not updating navigation proprties with automatic change tracking disabled - entity-framework

Question

I have one unitOfWork in my Domain Logic that retrieves tens of thousands of XML nodes, creates disconnected entities called retreivedBooks from the XML and updates Book entities in the database based on the retreivedBooks. For this particular unitOfWork's dbContext in my application, I have disabled change tracking due to very bad performance when there are lots of entities in the database. This has improved performance - great.
However it is no longer updating navigation properties. Here is a made up example to demonstrate the problem:
public class Book
{
public string Title;
public string Author;
public virtual List<Page> Pages;
}
_unitOfWork.Context.Configuration.AutoDetectChangesEnabled = false;
_unitOfWork.Context.Configuration.ValidateOnSaveEnabled = false;
foreach(Book retreivedBook in retreivedBooks )
{
Book existingBook= _unitOfWork.BookRepository.SingleOrDefault(b=>b.Id=retreivedBook.Id);
if(book!=null)
{
existingBook.Title=retreivedBook.Title;
existingBook.Author=retreivedBook.Author;
existingBook.Pages=retreivedBook.Pages;
_unitOfWork.Context.Entry(existingBook).State = EntityState.Modified;
}
}
_unitOfWork.Save();
In the example above, the Title and Author properties of books in the database get updated correctly, but the list of Pages does not.
By the way, I don't check for existing Pages based on retrieved Pages. We can assume that pages are always different every time so the book.Pages property will be replaced on every update.
Why does the pages property does not get updated in the database?

Answer 1

Due to the way Entity Framework works when you set _unitOfWork.Context.Configuration.AutoDetectChangesEnabled = false; it's much likely for the child entities to not get updated. In order to fix it should be enough to change the status to true before saving changes. In other words try this in your code:
...
_unitOfWork.Context.Entry(existingBook).State = EntityState.Modified;
}
}
_unitOfWork.Context.Configuration.AutoDetectChangesEnabled = true;
_unitOfWork.Save();