linq to EF4 查询中的 DbIsNullExpression 异常

Question

我已经编写了 linq EF4 查询，但它因异常而失败"DbIsNullExpression must refer to a primitive, enumeration or reference type." 的参数如下所示：

from listing in ctx.listingSource
join listingFile in ctx.ListingFiles
         .Where(x => companyIds.Contains(x.CompanyID.Value))
         .GroupBy(x => x.ListingID)
         .Select(x => new { ListingId = x.Key, Count = x.Count() }) on listing.ListingID equals listingFile.ListingId into listingFilesJoined
from listingFileJoined in listingFilesJoined.DefaultIfEmpty()
select new ListingDTO
{
    fileCount = listingFileJoined == null ? 0 : listingFileJoined.Count,
}

如何在不创建 class 而不是匿名类型的情况下解决此问题？

Answer 1

fileCount = (int?)listingFileJoined.Count ?? 0

Answer 2

如果不创建具体类型就无法 select 数据 =\ 修复如下：

.Select(x => new ConcreteType { ListingId = x.Key, Count = x.Count() })

也许这个答案对某人有帮助。

linq to EF4 查询中的 DbIsNullExpression 异常

DbIsNullExpression exception in linq to EF4 query

.net

c#

linq

entity-framework-4