Question

This has been driving me nuts for the last 2 days.
I have 3 pretty basic classes (well, reduced for readability)

public class Employee 
{
    public string Name { set; get; }
    virtual public Employer Employer { set; get; }

    public Employee(string name)
    {
        this.Name = name;
    }
}

,

// this basically ties Employee and his role in a company.
public class EmployeeRole{
    public int Id { set; get; }
    virtual public Employee Employee { set; get; }
    public string Role { set; get; }

    public EmployeeRole(Employee employee, string role){
        this.Employee = employee;
        this.Role = role;
    }
}

and

public class Employer{

    public string Name { set; get; }
    List<EmployeeRole> employees = new List<EmployeeRole>();
    virtual public List<EmployeeRole> Employees { get { return this.employees; } }

    public Employer(string name, Employee creator){
        this.Name = name;
        this.Employees.Add(new EmployeeRole(creator, "Creator"));
        creator.Employer = this;
    }
}

Seems pretty simple. Not doing any specific configuration for those classes in DbContext.

But, when I run following code

using (DbContext db = DbContext.GetNewDbContext()){

    Employee creator = new Employee("Bob");
    db.Employees.Add(creator);
    db.SaveChanges();

    Employer employer = new Employer("employer", creator);
    db.Employers.Add(employer);
    db.SaveChanges();
   // I know I can call SaveChanges once (and it actually works in this case), 
   // but I want to make sure this would work with saved entities.
}

It throws following exception:

Collection was modified; enumeration operation may not execute.

Stack trace:

at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource
resource) at
System.Collections.Generic.List1.Enumerator.MoveNextRare() at
System.Collections.Generic.List1.Enumerator.MoveNext() at
System.Data.Objects.ObjectStateManager.PerformAdd(IList1 entries)
at
System.Data.Objects.ObjectStateManager.AlignChangesInRelationships(IList1
entries) at System.Data.Objects.ObjectStateManager.DetectChanges()
at System.Data.Objects.ObjectContext.DetectChanges() at
System.Data.Entity.Internal.InternalContext.DetectChanges(Boolean
force) at
System.Data.Entity.Internal.Linq.InternalSet1.ActOnSet(Action action,
EntityState newState, Object entity, String methodName) at
System.Data.Entity.Internal.Linq.InternalSet1.Add(Object entity)
at System.Data.Entity.DbSet`1.Add(TEntity entity)

Anyone has an idea what’s going on and maybe how to fix it ?
Thanks !

Answer 1

I had the same problem. It looks like a bug in EF.

I changed my code to explicitly add the entity to EF context before setting it to any other entity property.