在EF6中更新外键对象

Question

I have following Models:

public class DivorceCases
{
  [Key]
  [Required]
  public string case_id { get; set; }
  public string archived { get; set; }
  public virtual Plaintiff p { get; set; }
}

public class Plaintiff{
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int id { get; set; }
    public string name { get; set; }
}

I am having a ModelView of DivorceCases for editing and in controller, I am using:

DivorceCases dcold = db.DivorceCase.Where(x => x.case_id == dc.case_id).Include(x => x.p).SingleOrDefault();
            dcold.p = dc.p;
            db.Entry(dcold).State = EntityState.Modified;
            db.SaveChanges();

When I update, instead of Updating the existing entry in Plaintiffs table, the EF6 inserts a new record in Plaintiffs table and updates the foreign key reference for this new record in DivorceCases table. What am I doing wrong? How do I get rid of that?

Answer 1

You are asking your attached case entity to link to an item that is not attached to the context.

Try to attach dc.p first or simply change the plaintiff id on the case instead of changing object.

Answer 2

Instead of assigning dc.p to dcold.p assign the properties of dc.p to dcold.p 's properties then call SaveChanges(); . you don't need db.Entry(dcold).State = EntityState.Modified; entity framework will update your data instead of creating new entry. Try the following code-

    DivorceCases dcold = db.DivorceCase.Where(x => x.case_id == dc.case_id)
            .Include(x => x.p).SingleOrDefault();
            dcold.p.name = dc.p.name;
            db.SaveChanges();

Answer 3

I got a solution after repeated debugging and hit and trials.

First of all I made a DBContextExtension Class like this:

public static T Modify<T>(this T t,T tnew)
    {
        PropertyInfo[] properties = typeof(T).GetProperties();
        foreach (PropertyInfo property in properties)
        {
            if (property.Name != "id" && (property.PropertyType==typeof(string) || property.PropertyType==typeof(DateTime)))
            {
                if (property.GetValue(tnew) != null)
                property.SetValue(t, property.GetValue(tnew));
            }
        }
        return t;
    }

Then for each foreign key referenced object, I called this Extension method and got 100% success.

DivorceCases dcold = db.DivorceCase.Where(x => x.case_id == dc.case_id).Include(x => x.p).SingleOrDefault();
            dcold = dcold.Modify(dc);
            dcold.p = dcold.p.Modify(dc.p);
            dcold.d = dcold.d.Modify(dc.d);
            db.SaveChanges();

Answer 4

maybe try this before your db.SaveChanges() call..

 db.p=db.Plaintiff.Where(x=>x.id==db.p.id);

Not sure if that'll work here. My database structure is slightly different. I'm storing foreign key ids in the linking table... I use that value passed in... (...Where(x=>x.id==PlaintiffID)