Updating many-to-many relationship

Question

I have a many-to-many relationship between Department objects and Grade objects, I am trying to update the Department by assigning a Grade . This is my update method:

public void UpdateDep(CommonLayer.Depratment UpDep)
{
    CommonLayer.Depratment CheckDepartment = this.getDepartment(UpDep.Department_GUID);
    this.Entities.Entry(CheckDepartment).CurrentValues.SetValues(UpDep);
    this.Entities.SaveChanges();

}

UpDep has the Grade id value but CheckDepartment is not being updated. No errors are being shown. I cannot understand what is wrong, as I have done this many times before.

Answer 1

Why not?

public void UpdateDep(CommonLayer.Depratment UpDep)
    {
        CommonLayer.Depratment CheckDepartment = this.getDepartment(UpDep.Department_GUID);
        this.Entities.Entry(CheckDepartment).CurrentValues.SetValues(UpDep);
        this.Entities.Entry(CheckDepartment).State = EntityState.Changed; 
        this.Entities.SaveChanges();

    }

notice the state.