How do I tell Autofixture to create objects with different IDs?

I have a simple setup method in my tests that creates two object instances (make by and Id

and Description

) and I did it using autofixture:

MyObject o1 = fixture.Create<MyObject>();
MyObject o2 = fixture.Create<MyObject>();

      

        
        
        
      

    

Next I try to save objects to db but I get duplicate key error, I debug the installation and see that o1 and o2 have the same Id

According to the Wiki , the number should be generated progressively:

Autogenerated Number

int autoGeneratedNumber = fixture.Create<int>();

Sample Result

int: 1, followed by 2, then by 3, etc.

      

        
        
        
      

    

but it looks like id doesn't work that way with object property, so now I am using this workaround:

MyObject o1= fixture.Build<MyObject>().With(x => x.Id, 1).Create();
MyObject o2= fixture.Build<MyObject>().With(x => x.Id, 2).Create();

      

        
        
        
      

    

but I don't like it very much

here can be used ISpecimenBuilder

to configure Autofixture to make it generate progressive id?

Additional Information:

this is my base test class:

public class BaseDBTest
{       
    public BaseDBTest()
    { }
    public Ploeh.AutoFixture.Fixture fixture { get { return new Fixture(); } }
}

      

        
        
        
      

    

and test setup:

[TestFixture]
public class MyObjectTests : BaseDBTest
{
    MyObject o1;
    MyObject o2;

    [TestFixtureSetUp]
    public void CreaDati()
    {
        o1= fixture.Create<MyObject >();
        o2= fixture.Create<MyObject >();
    }
}

      

        
        
        
      

    

weird things:

if i debug specific test objects created with different ids and random, but if i debug all tests of my project (with visual studio 2013 using Nunit runner) the ids are created equal

EDIT2

The definition of MyObject is quite complicated, sorry:

public class MyObject: LookUpObject<MyObject, int>
{
}

public abstract class LookUpObject<TObject, TKeyType> : EquatableObject<TObject>,     IKeyedEntity<TKeyType>
    where TObject : class
    where TKeyType : struct
{
    private TKeyType id;
    private string description;
    private bool isValid;

    public virtual TKeyType Id
    {
        get { return id; }
        set { id = value; }
    }

    public virtual string Description
    {
        get { return description; }
        set { description= value; }
    }
    public virtual bool IsValid
    {
        get { return isValid; }
        set { isValid= value; }
    }

    protected LookUpObject()
    {           
    }
}

      

        
        
        
      

    

EDIT 3

a picture of strange things with Nunit (I was afraid it might depend on Visual Studio),

single test run link

trial run of the project link