Entity Framework - Updating relationship by changing foreign key

Question

I have the two following models and DbContext:

    public class TestDbContext : DbContext
    {
        public IDbSet People { get; set; }
              


        

Answer 1

Try something like this :

    using (TestDbContext context = new TestDbContext())
            {
                foreach (Person person in People)
                {
                    if (!(context.People.Any(p => p.ID == person.ID)))
                        context.People.Add(person);
                    else
                    {
                        context.People.Attach(person);
                        context.Entry(person).State = System.Data.EntityState.Modified;
                    }
                    context.SaveChanges();
                }
                foreach (Car caar in Cars)
                {
                    if (!(context.Cars.Any(c => c.ID == caar.ID)))
                        context.Cars.Add(caar);
                    else
                    {
                        context.Cars.Attach(caar);
                        context.Entry(caar).State = System.Data.EntityState.Modified;
                    }
                    context.SaveChanges();
                }

            }

I think your error is due to the context.SaveChanges placements (and partialy your architecture). Consider using a dedicated method (a basic CRUD for instance) for each operation on your DB via Entity Framework. Hope this helps.

Edit : With a CRUD approch :

public class PersonManager // CRUD
    {
        public void Create(Person person)
        {
            using (TestDbContext context = new TestDbContext())
            {
                context.Person.Add(person);
                context.SaveChanges();
            }
        }

        public void Update(Person person)
        {
            using (TestDbContext context = new TestDbContext())
            {
                context.Person.Attach(person);
                context.Entry(person).State = System.Data.EntityState.Modified;
                context.SaveChanges();
            }
        }
    }

You could also make this class static in order to fit to your architecture.