Working on repayment frequency enumeration and its annual occurence, I came up with the
idea of implementing field attributes. Then found a good way to obtain the value of annual occurences which is embedded to the attribute. I implemented an enumeration extension to achieve this.
This is a neat and tidy way to enrich enumerations with custom attributes and get the values of these attributes by an enumeration extension.
The enumeration class:
namespace MyApplication.Domain.Enumerations
{
public enum RepaymentFrequency
{
[AnnualOccurence(12)]
[DaysImplied(30)]
Monthly,
[AnnualOccurence(52)]
[DaysImplied(7)]
Weekly,
.... ....
}
using System; namespace MyApplication.Domain.Enumerations { [AttributeUsage(AttributeTargets.Field)] public class AnnualOccurence : Attribute { public static readonly short Unassigned = -1; public AnnualOccurence() { _numberOfAnnualRepayments = Unassigned; } private short _numberOfAnnualRepayments; public short NumberOfAnnualRepayments { get { return _numberOfAnnualRepayments;} } public AnnualOccurence(short numberOfOccurences) { _numberOfAnnualRepayments = numberOfOccurences; } public override string ToString() { return "Annual Occurence = " + _numberOfAnnualRepayments.ToString(); } } }Now, there is a good way to get the values of such attributes from an 'enumeration instance', by implementing the following extension:
using System; using System.Linq; namespace HomeStart.LoanCalculators.Domain.Enumerations { public static class EnumExtensions { public static Expected GetAttributeValue<T, Expected>
(this Enum enumeration, Func<T, Expected> expression) where T : Attribute {
T attribute = enumeration.GetType().GetMember(enumeration.ToString())[0]
.GetCustomAttributes(typeof(T), false)
.Cast<T>().SingleOrDefault(); if (attribute == null) return default(Expected); return expression(attribute); } } }
with the following usage:
RepaymentFrequencyrepaymentFrequency =repaymentFrequency.Weekly;
...
var numberOfAnnualRepayments = repaymentFrequency.GetAttributeValue<AnnualOccurence, short> (x => x.NumberOfAnnualRepayments);var numberOfDaysImplied =
repaymentFrequency.GetAttributeValue<DaysImplied, short>
...(x => x.NumberOfDaysImplied);
where 52 will be assigned to numberOfAnnualRepayments,
and 7 will be assigned to numberOfDaysImplied in this case.
