linq到EF4查询中的DbIsNullExpression异常

Question

我已经写了linq EF4查询，但它失败了，异常＆＃34; DbIsNullExpression的参数必须引用原语，枚举或引用类型。＆＃34; 下面写的查询：

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,
}

如何在不创建类而不是匿名类型的情况下解决此问题？

Answer 1

没有创建具体类型= \无法选择数据 有修复方法：

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

也许这个答案对某人有帮助。