使用 EF 方法的 Linq 无法转换为存储表达式（在存储库模式中）

Question

我正在尝试使用 Ling 子查询从存储库模式中的多个模型访问数据。但是当我尝试使用 .GetQueryable() 访问内部查询中的数据时，我收到以下错误。

错误LINQ to Entities 无法识别方法 'System.Collections.Generic.List1[<>f__AnonymousType1702[System.Int32,System.Int32]] ToList[<>f__AnonymousType1702](System.Collections.Generic.IEnumerable1[<>f__AnonymousType170`2[System.Int32,System.Int32]])' 方法，并且此方法无法转换为存储表达式。

var query = (from i in
                                 (from student in _tblStudents.GetQueryable()
                                  join Sections in _tblStudentsSections.GetQueryable() on student.StudentID equals Sections.StudentID
                                  join Class in _tblClasses.GetQueryable() on Sections.ClassID equals Class.ClassID
                                  join Program in _tblPrograms.GetQueryable() on Class.ProgramID equals Program.ProgramID
                                  //where student.IsForeign == false
                                  select new
                                  {
                                      ProgramID = Program.ProgramID,
                                      program = Program.ProgramName,
                                      ClassIDs = Sections.ClassID,
                                      TotalSeats = Program.NoOfAdmissions,
                                      IsForeign = student.IsForeign
                                  })

                             group i by new { i.ProgramID, i.IsForeign, i.TotalSeats, i.program } into grp
                             select new AdmissionSummaryReportModel
                             {
                                 program = grp.Key.program,
                                 TotalSeats = grp.Key.TotalSeats,
                                 //SeatsFilled = grp.Select(m => m.ClassIDs).Count(),
                                 AvailableForeignSeats = 22,
                                 SeatsFilled = (int)(from student in _tblStudents.GetQueryable()
                                                            join StudentSections in _tblStudentsSections.GetQueryable() on student.StudentID equals StudentSections.StudentID
                                                            join Class in _tblClasses.GetQueryable() on StudentSections.ClassID equals Class.ClassID
                                                            join Program in _tblPrograms.GetQueryable() on Class.ProgramID equals Program.ProgramID
                                                     where student.IsForeign == false && Program.ProgramID == grp.Key.ProgramID
                                                            select new
                                                            {
                                                                StudentSections.ClassID
                                                            }).ToList().Count(),

                                 ForeignSeatsFilled = (int)(from student in _tblStudents.GetQueryable()
                                                            join StudentSections in _tblStudentsSections.GetQueryable() on student.StudentID equals StudentSections.StudentID
                                                            join Class in _tblClasses.GetQueryable() on StudentSections.ClassID equals Class.ClassID
                                                            join Program in _tblPrograms.GetQueryable() on Class.ProgramID equals Program.ProgramID
                                                            where student.IsForeign && Program.ProgramID == grp.Key.ProgramID
                                                            select new
                                                            {
                                                                StudentSections.ClassID
                                                            }).ToList().Count()

                             }).ToList();

如何使用 .GetQueryable() 克服此错误或为我提供任何替代方法

Answer 1

Queryable 在运行时被翻译成 sql 查询，在您使用 int 解析的子查询中，c# 编译器知道它不会查询翻译。用户 IEnumerable 或删除 int as count 将 return int.

Answer 2

问题是在您的 LINQ 查询中使用 ToList 函数，这不是您想要做的，因为它无法转换为正确的 SQL 查询。您只想在实际的 LINQ 查询之外使用 ToList。要获取计数 inside，请改用 LINQ Count 函数，例如：

select new                                                       
{

StudentSections.ClassID

}).Count()

使用 EF 方法的 Linq 无法转换为存储表达式（在存储库模式中）

Linq with EF method cannot be translated into a store expression(in repository pattern)

.net

c#

linq

entity-framework

repository-pattern