MCV6 EF Changing the sign of a decimal based on transaction type

Question

I'm storing transactions in an SQL database using EF code first and MVC6 I need to reverse the sign of the value based on the type of transaction. I want to do this at a central point so I don't have to make multiple changes throughout the app. i.e. on model creation or on the entity. Something like:

    public class Transactions : EntityBase
    {
        public TransactionType Type { get; set; }

        public decimal Amount
        {
            get
            {
                if (Type == Type.Refund && Amount > 0)
                    return Amount * -1;
                else
                    return Amount;
            }
            set { Amount = value; }
        }
    }

We could also store the value as a negative. Any suggestion on how best to achieve this?

Answer 1

You could go ahead and create an unmapped property and one that is filled by EF.

    public class Transactions : EntityBase
    {
        public TransactionType Type { get; set; }
        public RawAmount { get; set; }

        [NotMapped]
        public decimal Amount
        {
            get
            {
                if (Type == Type.Refund && RawAmount > 0)
                    return RawAmount * -1;
                else
                    return RawAmount;
            }
            set 
            { 
                Type = value > 0 ? Type.Expense : Type.Refund;
                Amount = Math.Abs(value); 
            }
        }
    }

If you are using fluent configurations in EF you could even make the RawAmount property protected, so it is not used by mistake.