Question

I have written a method to generate commission slips for tutors in a system for a college. Tutors have certain students enrolled with them at certain fees per month, and they earn a commission on these lessons they give. With this method, I am trying to calculate the total amount for ALL the enrollments belonging to the tutor (i.e. if they have 3 students and each student is enrolled for R460 a month, the total amount will be 1380 multiplied by their commission percentage.) Therefore, I want one commission slip generated (one database entry in the TutorCommission entity) for each tutor in the database with this total amount. Here is the code for this:

  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");
}
        }

At the moment, this code generates a new database entry for each enrollment (so if they have 20 enrollments, it will generate 20 database entries for the month). What changes can I make to this code that will put the total amount in one database entry for each tutor? Here are the relevant classes:

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; }

Thanks,
Amy

Answer 1

It looks like you have your collections specified the wrong way around – shouldnt you be joining a list of enrolments to a single tutor?:

IEnumerable<TutorCommission> tutorsCommissionsAlt = enrolments.GroupJoin(tutor ...

Should be:

IEnumerable<TutorCommission> tutorsCommissionsAlt = tutor.GroupJoin(enrolments...

I’ve put this code together, and it seems to check out:

        var month = DateTime.Now.ToString("MMMM");

        var enrolments = new List<Enrollment>();
        enrolments.Add(new Enrollment { TutorNoID = 1, MonthlyFee = 1500 });
        enrolments.Add(new Enrollment { TutorNoID = 1, MonthlyFee = 4500 });

        var tutor = new List<Tutor>();
        tutor.Add(new Tutor { TutorNoID = 1, TutorCommissionPercentage = 0.5 });


        IEnumerable<TutorCommission> tutorsCommissionsAlt = tutor.GroupJoin(enrolments,
                tut => tut.TutorNoID, 
                enr => enr.TutorNoID,
                (tut, enr) => new TutorCommission // Create entry which is the tutor and his total commission
                {
                    TutorNoID = tut.TutorNoID,
                    CommissionAmount = (long)enr.Sum(c => c.MonthlyFee * tut.TutorCommissionPercentage),
                    CommissionMonth = month,  // string constant 
                    CommissionStatus = "Unpaid",
                });


        foreach (var com in tutorsCommissionsAlt)
        {
            Console.WriteLine(com.CommissionAmount);
        }

// Output: 3000