一个数据库条目中的总金额- MVC 3

我为一所大学的系统编写了一个为导师生成佣金单的方法。导师每月收取一定的费用，让特定的学生注册，并从他们提供的课程中赚取佣金。通过这种方法，我试图计算所有导师注册的总金额(即如果他们有3个学生，每个学生每月注册R460，总金额将是1380乘以他们的佣金百分比。)因此，我希望为数据库中的每个导师生成一张佣金单(TutorCommission实体中的一个数据库条目)。下面是它的代码:

  public ActionResult CreateBulkCommissions()
        {
{
    var month = DateTime.Now.ToString("MMMM");
    var enrolments = db.Enrollments.ToList();
    var tutor = db.Tutors.ToList();
    IEnumerable<TutorCommission> tutorsCommissionsAlt = enrolments // Take the enrollments
        .GroupJoin( // This will group enrollments by the tutor
            tutor, // Join with the tutor's commission percentages.
            e => e.TutorNoID, // Use tutorNoID for left Key
            tcp => tcp.TutorNoID, // ... and right key
            (e, tcp) => new TutorCommission // Create entry which is the tutor and his total commission
            {
                TutorNoID = e.TutorNoID,
                CommissionAmount = (long)tcp.Sum(c => c.TutorCommissionPercentage * e.MonthlyFee),
                CommissionMonth = month,  // string constant 
                CommissionStatus = "Unpaid",
            });
    foreach (var com in tutorsCommissionsAlt)
    {
        db.TutorCommission.Add(com);
        db.SaveChanges();
    }
    return RedirectToAction("Index");
}
        }

目前，这段代码为每个登记生成一个新的数据库条目(因此，如果他们有20个登记，它将为当月生成20个数据库条目)。我可以对这段代码做什么更改，以便将每个导师的总金额放在一个数据库条目中?下面是相关的类:

public class Enrollment
{
    [Key]
    [Display(Name = "Enrollment ID Number")]
    public long EnrollmentIDNumber { get; set; }
    [Display(Name = "Client ID Number")]
    public long ClientNumberID { get; set; }
    [Display(Name = "Tutor ID Number")]
    public long TutorNoID { get; set; }
    [Display(Name = "Course Name")]
    public string CourseName { get; set; }
    [Display(Name = "Lesson Time")]
    public string LessonTime { get; set; }
    [Display(Name = "Lesson Day")]
    public string LessonDay { get; set; }
    [Display(Name = "Lesson Location")]
    public string LessonLocation { get; set; }
    [Display(Name = "Lesson Type")]
    public string LessonType { get; set; }
    [Display(Name = "Lesson Level")]
    public string LessonLevel { get; set; }
    [Display(Name = "Monthly Fee")]
    public long MonthlyFee { get; set; }
    public virtual Client Client { get; set; }
    public virtual Tutor Tutor { get; set; }
}
public class TutorCommission
{
    [Key]
    [Display(Name = "Commission ID")]
    public long CommissionID { get; set; }
    [Display(Name = "Commission Month")]
    public string CommissionMonth {get; set;}
    [Display(Name = "Commission Amount")]
    public double CommissionAmount { get; set; }
    [Display(Name = "Commission Status")]
    public string CommissionStatus { get; set; }
    [Display(Name = "Tutor ID Number")]
    public long TutorNoID { get; set; }
    public virtual Tutor Tutor { get; set; }
    public virtual ICollection<CommissionPayments> CommissionPayments { get; set; }
}
public class Tutor
{
    [Key]
    [Display(Name = "Tutor ID Number")]
    public long TutorNoID { get; set; }
    [Required]
    [StringLength(50, ErrorMessage="First name must be less than 50 characters")]
    [Display(Name = "First Name")]
    public string TutorFirstName { get; set; }
    [StringLength(50, ErrorMessage = "Last name must be less than 50 characters")]
    [Display(Name = "Last Name")]
    public string TutorLastName { get; set; }
    [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)]
    [Display(Name = "Birth Date")]
    public DateTime? TutorBirthDate { get; set; }
    [Display(Name = "Cellphone Number")]
    public string TutorCellphoneNumber { get; set; }
    [Display(Name = "Home Number")]
    public string TutorHomeNumber { get; set; }
    [RegularExpression("^[a-z0-9_''+-]+(''.[a-z0-9_''+-]+)*@[a-z0-9-]+(''.[a-z0-9-]+)*''.([a-z]{2,4})$", ErrorMessage = "Not a valid email address")]
    [Display(Name = "Email Address")]
    public string TutorEmailAddress { get; set; }
    [Display(Name = "Street Address")]
    public string TutorStreetAddress { get; set; }
    [Display(Name = "Suburb")]
    public string TutorSuburb { get; set; }
    [Display(Name = "City")]
    public string TutorCity { get; set; }
    [Display(Name = "Postal Code")]
    public string TutorPostalCode { get; set; }
    [Display(Name="Full Name")]
    public string FullName
    {
        get
        {
            return TutorFirstName + " " + TutorLastName;
        }
    }
    [Display(Name="Commission Percentage")]
    [Required]
    public double TutorCommissionPercentage { get; set; }
    public virtual ICollection<Enrollment> Enrollments { get; set; }
    public virtual ICollection<TutorCommission> TutorCommissions { get; set; }

谢谢,艾米