在linq查询中用字符串连接枚举

Question

I'm developing a WinForm application in c# with EF Code First Approach. The problem I have is when I do a linq query where a try to concat an Enum with a string. The error is as follows:

Unable to cast the type 'Entities.VoucherType' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types

Then I show the Enum, POCO Entities and linq query:

public enum VoucherType
{
    FAC = 1,
    BV,
    TKT,
    GR
}

public partial class Order
{
    public int OrderId { get; set; }
    public VoucherType VoucherType { get; set; }
    public string VoucherSeries { get; set; }
    public string VoucherNumber { get; set; }
}

public partial class Income
{
    public int IncomeId { get; set; }
    public int OrderId { get; set; }
    public decimal IncomeAmount { get; set; }
}

var q = from income in context.Incomes
        join order in context.Orders on income.OrderId equals order.OrderId
        select new
        {
            Voucher = order.VoucherType + "-" + order.VoucherSeries + "-" + order.VoucherNumber,
            Amount = income.IncomeAmount
        };

Answer 1

You could try this one:

var q = (from income in context.Incomes
         join order in context.Orders 
         on income.OrderId equals order.OrderId
         select new 
         {
             VoucherType = order.VoucherType,
             VoucherSeries = order.VoucherSeries,
             VoucherNumber = order.VoucherNumber,
             IncomeAmount = income.IncomeAmout
         }).AsEnumerable()
           .Select(x=> new
           {
               Voucher = x.VoucherType + "-" + x.VoucherSeries + "-" +x.VoucherNumber,
               Amount = x.IncomeAmount
           };