如何通过调用Entity Framework中的方法获取数据

Question

I want to get ResourceNames on the base of Id in EntityFramework but it is giving error: "LINQ to Entities does not recognize the method 'System.String GetResourceNameById(Int32)' method, and this method cannot be translated into a store expression." Following ismy code.

    public string  GetResourceNameById(int Id)
    {
        return _DBContex.Employees.Where(x => x.Id == Id).FirstOrDefault().FirstName;
    }


    public CygnusInternalResponseViewModel GetAllTimeEntriesForGrid(int start = 0, int perPage = -1, string sortColumn = "", string sortDirection = "")
    {
        List<TimeEntryViewModel> te = new List<TimeEntryViewModel>();

        te = (from jb in _DBContex.TimeEntries
             select new TimeEntryViewModel
             {
                 Id = jb.Id,

                 ResourceId = (int)jb.ResourceId,
                 TicketId = (int)jb.TicketId,
                 WorkType = (WorkTypeCatalog)jb.WorkType,
                 HoursWorked = (float)jb.HoursWorked,
                 Status = (TimeEntryStatusCatalog)jb.Status,
                 Role = (RoleCatalog)jb.Role,
                 StartTime = (TimeSpan)jb.StartTime,
                 EndTime = (TimeSpan)jb.EndTime,
                 SummaryNotes = jb.SummaryNotes,
                 InternalNotes = jb.InternalNotes,
                 Contract = (DateTime)jb.Contract,
                 Date = (DateTime)jb.Date,
                 ResourceName = GetResourceNameById((int)jb.ResourceId)    //   ERRORR Line

             }).ToList();

Answer 1

You might need to create in memory representation of your database table.

 public CygnusInternalResponseViewModel GetAllTimeEntriesForGrid(int start = 0, int perPage = -1, string sortColumn = "", string sortDirection = "")
    {
        List<TimeEntryViewModel> te = new List<TimeEntryViewModel>();
        var query=_DBContex.TimeEntries.ToList();//create in-memory representation
        te = (from jb in query
             select new TimeEntryViewModel
             {
                 Id = jb.Id,

                 ResourceId = (int)jb.ResourceId,
                 TicketId = (int)jb.TicketId,
                 WorkType = (WorkTypeCatalog)jb.WorkType,
                 HoursWorked = (float)jb.HoursWorked,
                 Status = (TimeEntryStatusCatalog)jb.Status,
                 Role = (RoleCatalog)jb.Role,
                 StartTime = (TimeSpan)jb.StartTime,
                 EndTime = (TimeSpan)jb.EndTime,
                 SummaryNotes = jb.SummaryNotes,
                 InternalNotes = jb.InternalNotes,
                 Contract = (DateTime)jb.Contract,
                 Date = (DateTime)jb.Date,
                 ResourceName = GetResourceNameById((int)jb.ResourceId)   
             }).ToList();

Answer 2

    te = (from jb in _DBContex.TimeEntries
         select new TimeEntryViewModel
         {
             Id = jb.Id,

             ResourceId = (int)jb.ResourceId,
             TicketId = (int)jb.TicketId,
             WorkType = (WorkTypeCatalog)jb.WorkType,
             HoursWorked = (float)jb.HoursWorked,
             Status = (TimeEntryStatusCatalog)jb.Status,
             Role = (RoleCatalog)jb.Role,
             StartTime = (TimeSpan)jb.StartTime,
             EndTime = (TimeSpan)jb.EndTime,
             SummaryNotes = jb.SummaryNotes,
             InternalNotes = jb.InternalNotes,
             Contract = (DateTime)jb.Contract,
             Date = (DateTime)jb.Date

         }).ToList();
    te.Foreach(t=>t.ResourceName = GetResourceNameById((int)t.ResourceId);

First you get the records then you set the ResourceName

Answer 3

您可以在SELECT之前调用ToList()方法，然后调用函数。