Question

我收到错误：

无法隐式将System.Collections.Generics.List<MeritMaste_QuestionPeparsettings>类型转换为System.Collections.Generics.List<MeritMaste.data.MeritMAster_QuestionPeparSettng>

是数据库连接问题吗？
是数据库连接错误吗？

public class DataManager
{
    public static void OnlineExamLists(
        out List<MeritMaste_QuestionPaperSettings> examQuestionSettings,
        out List<MeritMaster_QuestionBank> questionBanks, string examCode)
    {

        using (var dbcontext = new meritmasterEntities())
        {

            // var exam_code = dbcontext.MeritMaste_QuestionPaperSettings.Where(m => m.ID == examCode).FirstOrDefault().ex_code;
            //(from k in dbcontext.MeritMaste_QuestionPaperSettings where k.Status == true && k.ID == examCode select k.ex_code).ToList();

            examQuestionSettings = (from k in dbcontext.MeritMaste_QuestionPaperSettings 
                                    where k.Status == true && k.ex_code == examCode 
                                    select k).ToList();

            var examsettingslocal = examQuestionSettings.FirstOrDefault();

            var kabqu = new List<MeritMaster_QuestionBank>();
            var queBank = examsettingslocal == null
                ? kabqu
                : (from k in dbcontext.MeritMaster_QuestionBank
                    where k.Status == true && k.Course_ID == examsettingslocal.CourseId
                    select k).ToList();
            // questionBanks = queBank.ToList();

            var questionbanklocal = dbcontext.MeritMaste_QuestionPaperSettings.ToList();


            questionBanks = (from es in examQuestionSettings.ToList()
                                join qb in queBank.ToList() on new {p1 = (int) es.CourseId, p2 = (int) es.QuestionIds} equals
                                    new {p1 = (int) qb.Course_ID, p2 = (int) qb.ID}

                                where es.ex_code == examCode && es.Status == true && qb.Status == true
                                select qb).ToList();
            //join a in questionpaperlocal.ToList() on k.QuestionIds equals a.ID
            //where k.Status == true && a.Status == true
            ////orderby a.Id ascending
            //select k
        }
    }
}

Answer 1

MeritMaste_QuestionPeparsettings和MeritMaste.data.MeritMAster_QuestionPeparSettng是编译器的两种不同类型，并且在这两种类型之间不存在转换。

您需要定义转换（隐式或显式），或手动转换它们。您可以使用各种技术执行此操作，例如使用IQueryable.ForAll或IEnumerable.Select扩展方法。

不能隐式转换类型＆nbsp; syste.collections.generics.list＆＃39;到＆＃39; system.collections.generics.list＆＃39;

1 个答案: