Create object that inherit the interface

Question

I have two model interface ILoanModel and IAmortizationModel.

public interface ILoanModel
{
    string ID { get; set; }
    IEmployeeModel Borrower { get; set; }
    // ******* other propeties *********
    ICollection<Model.IAmortizationModel> AmortizationTable { get; set; }
}

public interface IAmortizationModel
{
    string ID { get; set; }
    ILoanModel Loan { get; set; }
    // ******* other propeties *********
}

I create another interface that will handle the computation and other function

public interface IAmortization
{
    // Compute and generate amortization table
    Model.ILoanModel Generate(Model.ILoanModel loan);
    // **** Other function *****
}

Currently I have 3 type of loans and all them have same way of computation and generation of amortization table.

public abstract class Amortization : Controller.Computation.Interface.IAmortization
{
    public virtual Model.ILoanModel Generate(Model.ILoanModel loan)
    {
        // **** other code *******
        //Create the amortization table
        decimal last_Amortization_RunningBalance = loan.Amount;
        loan.AmortizationTable = new List<Model.IAmortizationModel>();

        for (int x = 1; loan.NumberOfPayment >= x; x++)
        {
            // having problem here because Model.IAmortizationModel is a interface
            var newAmortizationRow = new Model.IAmortizationModel
            {
                ID = Guid.NewGuid().ToString(),
                AmortizationAmount = loan.AmortizationPaymentAmount,
                AmortizationInterest = loan.AmortizationPaymentAmount* loan.Nominal,
                AmortizationPrepayment = 
                    loan.AmortizationPaymentAmount 
                    - (loan.AmortizationPaymentAmount * loan.Nominal),
                AmortizationOutstandingBalance = 
                    last_Amortization_RunningBalance 
                    - (loan.AmortizationPaymentAmount 
                        - (loan.AmortizationPaymentAmount * loan.Nominal)),
                Sequence = x
            };

            last_Amortization_RunningBalance -= 
                newAmortizationRow.AmortizationOutstandingBalance;
            loan.AmortizationTable.Add(newAmortizationRow);
        }
    }
}

My problem now is generating new IAmortizationModel that will be added to the loan.AmortizationTable. How can I get the type of loan.AmortizationTable and create?

Why are you using interfaces? Do you have multiple implementations of the loan model and amortization model? If you do, and you really need to instantiate an object you could make the method generic and add a `new()` constraint to it. — Ian Mercer, May 19 '21 at 03:17
@IanMercer yes, sample the car loan and emergency loan. car loan have field where need to specify the car brand and model while the emergency loan need what emergency occurred. — Vic, May 19 '21 at 03:25
IMHO add a `protected abstract IAmortizationModel Factory(...)` method. — Jeremy Lakeman, May 19 '21 at 04:14

score 1 · Accepted Answer · answered May 19 '21 at 03:41

One option would be to make it generic and add a generic constraint with new():

public virtual Model.ILoanModel Generate<T>(Model.ILoanModel loan)
   where T:IAmortizationModel, new()

and then call new T()

An alternative option would be to pass a generator function:

public virtual Model.ILoanModel Generate(Model.ILoanModel loan,
  Func<IAmortizationModel> generator)

and call generator()

Create object that inherit the interface

1 Answers1