What is the best method for attaching a single key/value pair attribute to an enumeration?
[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();
    }
}

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