Question

I’m new to the Entity Framework. I’m using to work with the database in a WPF application. I’ve created a model as in this blog, and I now want to use it in my application.

I know how to retrieve and modify entities like this:

DatabaseContext ct = new DatabaseContext();
var person = ct.Persons.Find(1);
person.Name = "NewName";
ct.SaveChanges();

However, in an application that waits for user input, this means keeping the datacontext around in the ViewModel, which isn’t very desirable. Instead, I want to do something like this:

class PersonViewModel {

    Person psn;

    public PersonViewModel(int PersonId) {
         DatabaseContext ct = new DatabaseContext();
         psn = ct.Persons.Find(1);
    }

    public Save() {
        DatabaseContect ct = new DatabaseContext();
        ct.Persons.Update(psn); // (There is no Update() method.)
        ct.SaveChanges();
    }

}

I don’t know how to do Update().

I have the DatabaseContext defined like this:

public partial class DatabaseContext: DbContext
{
    public DbSet<Person> Persons { get; set; }
}

but I don’t seem to have DatabaseContext.ObjectStateManager, which some people use in solutions to similar problems. I don’t know why this is – is it related to using POCO objects?

How should I solve this?

Answer 1

As an alternative to Attach:

public Save() {
    DatabaseContect ct = new DatabaseContext();
    ct.Entry(psn).State = EntityState.Modified;
    ct.SaveChanges();
}