CODEWITHSUNDEEP
c#asp.net-mvc-3entity-framework
Csati
Csati

Reputation: 1271

ASP.NET MVC with Entity Framework - Update/Save complex type property

I have 3 classes, related to 3 database tables:

public class Stat
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<Quantity> Quantities { get; set; }
}
public class Quantity
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual Stat Stat { get; set; }
    public virtual Unit Unit { get; set; }
}
public class Unit
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Abbreviation { get; set; }
    public List<Quantity> Quantities { get; set; }
}

A Stat can have a list of Quantities, and a Quantity have one Unit. If I want to save a Stat with Entity Framework, I have to iterate through its list of Quantities, and check if the Quantity already exists, or newly created (the data comes from an HTML Form).

public void UpdateStat(Stat stat)
{
    foreach (Quantity q in stat.Quantities)
    {
        if (q.Id == 0)
        {
            db.Quantities.Add(q);
        }
        else
        {
            db.Entry(q).State = EntityState.Modified;
        }
    }
    db.Entry(stat).State = EntityState.Modified;
    db.SaveChanges();
}

The problem is, when more Quantities have the same Unit, an error occurs: "An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key."

I have no idea, how a Stat can be updated with the list of its Quantities and Units together.

Upvotes: 4

Views: 2175

Answers (1)

nhrobin
nhrobin

Reputation: 903

As you mentioned, the problem occurs when more than one quantity has same Unit. To avoid adding same unit multiple time you can check if a unit is already in the db. If it exists then reuse the existing unit. 

if (q.Id == 0)
{
   var unit=db.Units.FirstOrDefault(u=>u.Id==q.Unit.Id);
   if(unit!=null)
      q.Unit=unit;
   db.Quantities.Add(q);
}

Upvotes: 1

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