C# 无法将OneTimeEnumerable强制转换为System.Collections.Generic.List

因此，我目前正在使用MSSQL数据库后端开发一个小型客户端应用程序

我一直在使用LINQtoSQL，其中

CompiledQuery

。但是，当从数据库检索对象列表时，我得到一个

InvalidCastException

，并显示以下消息：

Unable to cast object of type 'OneTimeEnumerable`1[DiallerBlacklistManager.Data.Entities.BlacklistDataContext.BlacklistEntry]' to type 'System.Collections.Generic.List`1

这是我第一次遇到这个错误，我有点不知道它指的是什么

我编译的查询函数如下所示：

    public static Func<BlacklistDataContext, DateTime, DateTime, List<BlacklistEntry>>
        GetBlacklistEntriesByBlacklistDateRangeFunc =
            CompiledQuery.Compile<BlacklistDataContext, DateTime, DateTime, List<BlacklistEntry>>(
                (db, startTime, endTime) =>
                    (from BlacklistEntry e in db.BlacklistEntries
                        where e.BlacklistDate >= startTime && e.BlacklistDate <= endTime
                        select e).ToList());

有人能告诉我们什么是

OneTimeEnumerable

，以及为什么结果集不是Func类型参数中定义的类型吗

---

提前谢谢。

这以前发生在我身上。问题的原因是编译的查询块中的

ToList

。编译后的查询显然只返回

OneTimeEnumerable

，而不是

List

。删除

ToList

，让编译后的查询返回

IEnumerable

，然后在调用编译后的查询后调用

ToList

public static Func<BlacklistDataContext, DateTime, DateTime, IEnumerable<BlacklistEntry>>
    GetBlacklistEntriesByBlacklistDateRangeFunc =
        CompiledQuery.Compile<BlacklistDataContext, DateTime, DateTime, List<BlacklistEntry>>(
            (db, startTime, endTime) =>
                from BlacklistEntry e in db.BlacklistEntries
                where e.BlacklistDate >= startTime && e.BlacklistDate <= endTime
                select e);

public class BlacklistEntryDisplayItem
{
    public BlacklistEntryDisplayItem(int id, string phoneNumber, DateTime blacklistDate, string comments, int userId, bool deleted)
    {
        Id = id;
        PhoneNumber = phoneNumber;
        BlacklistDate = blacklistDate;
        Comments = comments;
        UserId = userId;
        Deleted = deleted;
    }

    public int Id { get; private set; }

    public string PhoneNumber { get; private set; }

    public DateTime BlacklistDate { get; private set; }

    public string Comments { get; set; }

    public int UserId { get; private set; }

    public bool Deleted { get; set; }

    public static implicit operator BlacklistEntryDisplayItem(BlacklistEntry entry)
    {
        return new BlacklistEntryDisplayItem(
            entry.Id, 
            entry.PhoneNumber, 
            entry.BlacklistDate, 
            entry.Comments, 
            entry.UserId, 
            false);
    }

    public static implicit operator BlacklistEntryDisplayItem(DeletedBlacklistEntry entry)
    {
        return new BlacklistEntryDisplayItem(
            entry.Id,
            entry.PhoneNumber,
            entry.BlacklistDate,
            entry.Comments,
            entry.UserId,
            true);
    }
}

public static Func<BlacklistDataContext, DateTime, DateTime, IEnumerable<BlacklistEntry>>
    GetBlacklistEntriesByBlacklistDateRangeFunc =
        CompiledQuery.Compile<BlacklistDataContext, DateTime, DateTime, List<BlacklistEntry>>(
            (db, startTime, endTime) =>
                from BlacklistEntry e in db.BlacklistEntries
                where e.BlacklistDate >= startTime && e.BlacklistDate <= endTime
                select e);

GetBlacklistEntriesByBlacklistDateRangeFunc(dataContext, startTime, endTime).ToList()