Entity Framework System.InvalidOperationException : 'An entity object cannot be referenced by multiple instances of IEntityChangeTracker.'

Question

I'm using EntityFramework with ASP.Net MVC project I have 3 projects in my solution :

• Web project ASP.net MVC
• Domain project where there is all class
• Data project where there is my DbContext and request DB

I have 2 class :

• User
• Folder

When I want to create Folder I want Id User to associate User with the folder. So in my class Folder I have this attribut to make relation :

public virtual User user  {get; set; }

When I want to add folder in DB I have an error at this line :

_dbSet.Add(entity);

Error is : System.InvalidOperationException : 'An entity object cannot be referenced by multiple instances of IEntityChangeTracker.'

This is the method

 public void Insert(TEntity entity)
        {
            if (entity == null)
                throw new ArgumentNullException("entity");

            try
            { 
                    _dbSet.Add(entity);
                    _dbContext.SaveChanges();
            }
            catch (DbEntityValidationException ex)
            {
                ThrowValidationError(ex);
            }
        }

I think I don't use the same DbContext but I don't know how keep the same DbContext when I use many entities (User and Folder)

Answer 1

I try to answer your last question.

I think I don't use the same DbContext but I don't know 
how keep the same DbContext when I use many entities (User and Folder)

Your Context can have multiple DbSet. It seems you have only one, since you call it "_dbSet". I suggest you name one DbSet "Users" and one DbSet "Folders". Then you can easily access users and folders with one context.

Here is the code in VB.net:

Public Class MyContext 
    Inherits DbContext

    Public Property Users As DbSet(of User)
    Public Property Folders As DbSet(of Folder)
End Class

and c#:

public class MyContext : DbContext
{

    public DbSet<User> Users { get; set; }
    public DbSet<Folder> Folders { get; set; }
}

Please post the source code of your current context class, if you have more questions regarding this.