What is the best method for attaching a single key/value pair attribute to an enumeration?

Question

I'm trying to figure out what the best method is for attaching a single key/value pair attribute to an enumeration where the key is my MerchantId and the value is the corresponding TransactionKey.

What I currently do is put a comma delimited string into a StringValueAttribute class:

Public Enum Merchants
    <StringValue("coke,faj80785hq+faf=-1=-jfa+">
        Coke = 0
    <StringValue("pepsi,adfji=-901jnas++fdj98ua")>
        Pepsi = 1
    <StringValue("drpepper,jk878-=+9kdkdja0=a=f--daj")>
        DrPepper = 2
End Enum

Public Property Merchant As Merchants

I pull out the key or MerchantId by calling .GetStringValue().Split(","c)(0):

Public ReadOnly Property MerchantId() As String
    Get
        Return Merchant.GetStringValue().Split(","c)(0)
    End Get
End Property

I pull out the value or TransactionKey by calling .GetStringValue().Split(","c)(1):

Public ReadOnly Property TransactionKey() As String
    Get
        Return Merchant.GetStringValue().Split(","c)(1)
    End Get
End Property

---

Is this the most efficient way to do this? Instead of StringValueAttribute, what about creating an attribute using a Dictionary(Of String, String) since it is a key/value pair list? Or String Array or List? Maybe something in LINQ? Or is it simply already efficient as it can be?

Answer 1

I would suggest creating your own attribute class which takes both values in a type-safe manner and names them appropriately. Or, if not every item will have both values, create two separate attributes, one for each value.

Or better yet, don't use an Enum at all. Create your own class that takes all three values in the constructor and then create a class with shared properties for each item, as such:

Public Class Merchants
    Public Shared ReadOnly Property Coke() As Merchant
        Get
            Return _coke
        End Get
    End Property
    Private Shared _coke = New Merchant(0, "Coke", "faj80785hq+faf=-1=-jfa+")

    ...
End Class

Answer 2

You can use the following custom attribute and extension methods to get the values. Some things to note:

• It's in C#, hope that's ok :)

• The extension methods class caches the MerchantIds and TransactionIds in static scope, so should be pretty efficient.

• You get the MerchantId by calling (e.g.) Merchants.Coke.GetMerchantId();.

• You get the TransactionId by calling (e.g.) Merchants.Coke.GetTransactionId();.

Also, the extension methods don't bother checking that the Merchants value passed to them is valid, so you could break it by calling ((Merchants)76282).GetMerchantId().

[AttributeUsage(AttributeTargets.Field)]
public class MerchantDataAttribute : Attribute
{
    public MerchantDataAttribute(string merchantId, string transactionId)
    {
        this.MerchantId = merchantId;
        this.TransactionId = transactionId;
    }

    public string MerchantId
    {
        get;
        private set;
    }

    public string TransactionId
    {
        get;
        private set;
    }
}

public static class MerchantsExtensions
{
    private static readonly Dictionary<Merchants, MerchantDataAttribute> 
        _merchantsCache = CacheMerchantsCache();

    public static string GetMerchantId(this Merchants merchants)
    {
        return _merchantsCache[merchants].MerchantId;
    }

    public static string GetTransactionId(this Merchants merchants)
    {
        return _merchantsCache[merchants].TransactionId;
    }

    private static Dictionary<Merchants, MerchantDataAttribute> CacheMerchantsCache()
    {
        return Enum.GetValues(typeof(Merchants))
            .Cast<Merchants>()
            .Select(m => new
            {
                Merchant = m, 
                MerchantAttribute = GetMerchantAttribute(m)
            })
            .ToDictionary(m => m.Merchant, m => m.MerchantAttribute);
    }

    private static MerchantDataAttribute GetMerchantAttribute(Merchants merchant)
    {
        return typeof(Merchants)
            .GetMember(merchant.ToString())
            .First()
            .GetCustomAttributes(typeof(MerchantDataAttribute), inherit: false)
            .Cast<MerchantDataAttribute>()
            .First();
    }
}

Answer 3

For any future visitors, I thought I'd post the VB version of the answer, since that's what I tagged the question with. Also, I had to do things slightly different due to VB requiring extensions to be inside of a Module.

Here is the Module:

(I used a lot of line continuation for easier readability. Also, for the sake of readability in this example I imported SomeClass so that I didn't have to type out that NameSpace)

Imports SomeClass

Module MerchantsExtensions

    Private ReadOnly MerchantsCache _
        As Dictionary(Of Merchants, MerchantDataAttribute) _
        = CacheMerchantsCache()

    Private Function CacheMerchantsCache() _
        As Dictionary(Of Merchants, MerchantDataAttribute)

        Return [Enum].GetValues(GetType(Merchants)) _
            .Cast(Of Merchants)() _
            .Select(Function(m) New With
            {
                .Merchant = m,
                .MerchantAttribute = GetMerchantAttribute(m)
            }) _
            .ToDictionary(Function(m) m.Merchant, _
                          Function(m) m.MerchantAttribute)

    End Function

    Private Function GetMerchantAttribute(merchant As Merchants) _
        As MerchantDataAttribute

        Return GetType(Merchants) _
            .GetMember(merchant.ToString()) _
            .First() _
            .GetCustomAttributes(GetType(MerchantDataAttribute), _
                                 inherit:=False) _
            .Cast(Of MerchantDataAttribute)() _
            .First()

    End Function

    <Runtime.CompilerServices.Extension()>
    Public Function GetMerchantId(merchants As Merchants) As String

        Return MerchantsCache(merchants).Id

    End Function

    <Runtime.CompilerServices.Extension()>
    Public Function GetTransactionKey(merchants As Merchants) As String

        Return MerchantsCache(merchants).TransactionKey

    End Function

End Module

Here is the implementation of the extension methods in a class I named SomeClass for this example:

Public Class SomeClass

    Public Enum Merchants
        <MerchantData("coke", "faj80785hq+faf=-1=-jfa+")>
            Coke = 0
        <MerchantData("pepsi","adfji=-901jnas++fdj98ua")>
            Pepsi = 1
        <MerchantData("drpepper","jk878-=+9kdkdja0=a=f--daj")>
            DrPepper = 2
    End Enum

    <AttributeUsage(AttributeTargets.Field)>
    Public Class MerchantDataAttribute : Inherits Attribute

        Public Sub New(merchantId As String, transactionKey As String)
            _Id = merchantId
            _TransactionKey = transactionKey
        End Sub

        Public Property Id() As String
        Public Property TransactionKey() As String

    End Class

End Class