Question

I’m a novice, so I guess in the code I’m about to present, ther’re going to be lots of violations in terms of ‘proper code’. (be glad to get any remark..)

I have three entites:

public class Person
{
    public int PersonId { get; set; }
    public int AgeId { get; set; }
    ...//some properties
}

public class Age
{
    public int AgeId { get; set;}
    public int PersonsId { get; set; }

    ...//some properties

    public virtual ICollection<AgeRange> AgeRanges {get; set;}

}


public class AgeRange
{
    public string AgeRangeId { get; set; }
    public string Value { get; set; }

    ICollection<Age> Ages { get; set; }

}

I created a new ‘Age’ entity, set it’s properies with values, then, insert to its ‘Icollection’ some ‘AgeRange’ entities, which I pull out of DB. (they already exist)
I add the new ‘Age’ to dbContex, and when perform ‘savechanges’ I get exception:

Violation of PRIMARY KEY constraint 'PK_AgeRanges'. Cannot insert duplicate key in  object 'dbo.AgeRanges'.
The statement has been terminated. 

(AgeRange PK is string on purpose, as my intention is to keep them constant on a logic basis)

here’s the rest of the code:

[HttpPost]
public ActionResult AddPerson(AddPersonViewModel vm)
 {

         if (ModelState.IsValid)
         {   
             Services services = new Services();
             Age age = services.GetAgeEntity(vm.Ages); 
             db.Ages.Add(age);
             db.SaveChanges(); //exception apears here.
             ........

         }

public class Services
{
    ModelContext db;

    public Services()
    {
        db = new ModelContext();
    }

    public Age GetAgeEntity(string[] ages)
    {
        Age age = new Age();

        //some more code...

        age.AgeRanges = GetAgeRanges(ages);   
        return age;
    }

        }



    ICollection<AgeRange> GetAgeRanges(string[] ages)
    {
        Age age = new Age();
        age.AgeRanges = new List<AgeRange>();

        foreach (string item in ages)
        {
            var ageRange = db.AgeRanges.Find(item);
            age.AgeRanges.Add(ageRange);
        }

        return age.AgeRanges;
    }

Any help will be appreciated.

Answer 1

You are having this error because you are using two different contexts: One the read the AgeRange entities from the database: It’s the ModelContext db private member in your Services class which you create in the constructor:

db = new ModelContext();

And a second context to add the Age entity together with the AgeRange collection you are using in the controller action:

db.Ages.Add(age);

This cannot be the same db instance. The second context does not know anything about the AgeRange entities because they have been loaded in another context. Hence SaveChanges tries to insert them as new entities.

You could create two additional methods in your Services class:

public void AddAgeEntity(Age age)
{
    db.Ages.Add(age);
}

public void SaveChanges()
{
    db.SaveChanges();
}

And in your controller:

Services services = new Services();
Age age = services.GetAgeEntity(vm.Ages); 
services.AddAgeEntity(age);
services.SaveChanges();

Now the whole operation uses the same context and your code should work.