LINQ Datacontext处理问题

Question

我得到一个Cannot access object: DataContext after it's been disposed在下面的DAL方法之后。 我以为我可以在那里打电话处理。 result是一个IEnumurable ，我认为它是IQueryable导致这些问题。

我究竟做错了什么？ 我应该如何处理我的DataContext 。 有没有更好的东西返回DataTable ？ 这是一个指向SQL 2005的桌面应用程序。

导致此错误的示例方法 - >

---

    public static DataTable GetEnrolledMembers(Guid workerID)
    {
        var DB = CmoDataContext.Create();

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

        var result = from enrollee in AllEnrollees.AsEnumerable()
                     where (enrollee.DisenrollmentDate == null || enrollee.DisenrollmentDate > DateTime.Now)
                     //let memberName = BLLConnect.MemberName(enrollee.ClientID)
                     let lastName = BLLConnect.MemberLastName(enrollee.ClientID)
                     let firstName = BLLConnect.MemberFirstName(enrollee.ClientID)
                     orderby enrollee.DisenrollmentDate ascending, lastName ascending
                     select
                         new
                         {
                             enrollee.ClientID,
                             //MemberName = memberName,
                             LastName = lastName,
                             FirstName = firstName,
                             NurseName = BLLAspnetdb.NurseName(enrollee.CMONurseID),
                             SocialWorkerName = BLLAspnetdb.SocialWorkerName(enrollee.CMOSocialWorkerID),
                             enrollee.EnrollmentDate,
                             enrollee.DisenrollmentDate,
                             ESWorkerName = enrollee.ESFirstName + " " + enrollee.ESLastName,
                             enrollee.ESPhone
                         };
        DB.Dispose();

        return result.CopyLinqToDataTable();
    }

我创建DataContext的分部类 - >

---

partial class CmoDataContext
{
    public static bool IsDisconnectedUser
    {
        get
        {
            return Settings.Default.IsDisconnectedUser;
        }
    }

    public static CmoDataContext Create()
    {
        var cs = IsDisconnectedUser ? Settings.Default.CMOConnectionString : Settings.Default.Central_CMOConnectionString;
        return       new CmoDataContext(cs);
    }

Answer 1

在处理DataContext之后，您正在调用CopyLinqToDataTable 。 由于LINQ使用延迟执行，它仅当执行该查询result被列举在DataContext设置之后。

您应该将DataContext放在包含return语句的using块中。
这将在调用CopyLinqToDataTable之后CopyLinqToDataTable DataContext，从而避免此问题。

例如：

using(var DB = CmoDataContext.Create()) {
    //Execute queries
    return result.CopyLinqToDataTable();
}

using语句生成一个finally块，在using块的末尾处理DataContext。 （即使抛出异常）

Answer 2

在调用Dispose之前，您应该在查询中使用类似ToList

Answer 3

你不能这样做吗？

...
DataTable dt = result.CopyLinqToDataTable(); 
DB.Dispose(); 
return dt;