c# - 嵌套 LINQ 方法抛出 `Not Supported...` 异常

Question

这是这里的后续内容 --> multiple-sorting-on-linq-nested-method .

基本上，在 let memberName = ... 上，它抛出此异常 Method 'System.String MemberName(Int32)' 不支持对 SQL 的转换。 并且我我没有找到解决方案。

此外，BLLCmo 和 BLLConnect 实际上使用两个不同的数据库。原来的应用程序(不是我的)使用 4 个独立的数据库，所以我试图按时完成。

---

BLLCmo.cs

    public static DataTable GetAllMembers(Guid workerID)
    {
        var AllEnrollees = from enrollment in context.tblCMOEnrollments
                               where enrollment.CMOSocialWorkerID == workerID || enrollment.CMONurseID == workerID
                               join supportWorker in context.tblSupportWorkers on enrollment.EconomicSupportWorkerID equals supportWorker.SupportWorkerID into workerGroup
                               from worker in workerGroup.DefaultIfEmpty()
                               let memberName = BLLConnect.MemberName(enrollment.ClientID)
                               orderby enrollment.DisenrollmentDate ascending, memberName ascending 
                               select new
                                       {
                                           enrollment.ClientID,
                                           MemberName = memberName,
                                           NurseName = BLLAspnetdb.NurseName(enrollment.CMONurseID),
                                           SocialWorkerName =BLLAspnetdb.SocialWorkerName(enrollment.CMOSocialWorkerID),
                                           enrollment.DisenrollmentDate,
                                           enrollment.EnrollmentDate,
                                           ESFirstName = worker.FirstName,
                                           ESLastName = worker.LastName,
                                           ESPhone = worker.Phone
                                       };

        var dataTable = AllEnrollees.CopyLinqToDataTable();

        return dataTable;
    }

---

BLLConnect.cs

    public static String MemberName(Int32 personID)
    {
        var memberName = from person in context.tblPersons
                         where person.PersonID == personID
                         select person.FirstName + " " + person.LastName;

        return memberName.SingleOrDefault();
    }

Answer 1

问题在于 LINQ to SQL 正在尝试将您的方法转换为 SQL。由于 MemberName 不是有效的 SQL，因此它放弃。相反，您需要从 SQL 中提取所需的数据，然后在单独的 LINQ to Objects 查询中调用您的方法(并排序):

public static DataTable GetAllMembers(Guid workerID)
{
    var AllEnrollees =
        from enrollment in context.tblCMOEnrollments
        where enrollment.CMOSocialWorkerID == workerID || enrollment.CMONurseID == workerID
        join supportWorker in context.tblSupportWorkers on enrollment.EconomicSupportWorkerID equals supportWorker.SupportWorkerID into workerGroup
        from worker in workerGroup.DefaultIfEmpty()
        select new
        {
            enrollment.ClientID,
            enrollment.CMONurseID,
            enrollment.CMOSocialWorkerID,
            enrollment.DisenrollmentDate,
            enrollment.EnrollmentDate,
            ESFirstName = worker.FirstName,
            ESLastName = worker.LastName,
            ESPhone = worker.Phone
        };

    var result =
        from enrollee in AllEnrollees.AsEnumerable()
        let memberName = BLLConnect.MemberName(enrollee.ClientID)
        orderby enrollee.DisenrollmentDate ascending, memberName ascending 
        select new
        {
            enrollee.ClientID,
            MemberName = memberName,
            NurseName = BLLAspnetdb.NurseName(enrollee.CMONurseID),
            SocialWorkerName = BLLAspnetdb.SocialWorkerName(enrollee.CMOSocialWorkerID),
            enrollee.DisenrollmentDate,
            enrollee.EnrollmentDate,
            enrollee.ESFirstName,
            enrollee.ESLastName,
            enrollee.ESPhone
        };

    return result.CopyLinqToDataTable();
}