Question

我有一个LINQ查询，用于填充 StaffHierarchySearchViewModel 的视图模型。我试图在我的业务逻辑层（BLL）中填充 StaffHierarchySearchViewModel 并将这些结果返回给我的控制器。当我尝试在我的方法中返回结果值时，我在返回结果行上收到错误。我收到错误：Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<WebReportingToolDAL.Models.ViewModels.StaffHierarchySearchViewModel>' to 'WebReportingToolDAL.Models.ViewModels.StaffHierarchySearchViewModel'. An explicit conversion exists (are you missing a cast?)'我尝试了其他解决方法，但我仍然无法获得返回值。

namespace WebReportingToolBLL
{
 public class StaffHierarchySearch
  {
    private Collections_StatsEntities db = new Collections_StatsEntities();

    public StaffHierarchySearchViewModel StaffHierarchySearchViewModel(string SearchString)
    {
        IEnumerable<StaffHierarchySearchViewModel> results = from sa in db.SecurityAccesses
                     join ss in db.SecuritySystems on sa.System equals ss.SystemID
                     join s in db.Staffs on sa.EmpID equals s.EmpID
                     join u in db.Units on s.UnitID equals u.UnitID
                     join h in db.Hierarchies on sa.EmpID equals h.EmpID
                     join t in db.Staffs on h.TeamID equals t.EmpID
                     where sa.ID == SearchString
                     select new WebReportingToolDAL.Models.ViewModels.StaffHierarchySearchViewModel
                     {
                         ID = sa.ID,
                         SystemName = ss.SystemName,
                         LastName = s.LastName,
                         FirstName = s.FirstName,
                         UnitName = u.UnitName,
                         EffectiveStart = h.EffStart,
                         EffectiveEnd = h.EffEnd,
                         ManagerFirstName = t.FirstName,
                         ManagerLastName = t.LastName,
                         Search = SearchString
                     };

        return results;
    }

}

}

Answer 1

public StaffHierarchySearchViewModel StaffHierarchySearchViewModel(string SearchString)
{
    IEnumerable<StaffHierarchySearchViewModel> results = from sa in db.SecurityAccesses
 /// snip 
    return results;
}

results是IEnumerable<>。该函数只想返回一个。

return results.FirstOrDefault();会让它进行编译，但这并不是你想要的，因为你真的想要集合中的所有项目。

更改方法返回类型 - 以及视图中的@model语句 - 以反映它是IEnumerable。

Answer 2

关于@James Curran所说的内容，我将方法返回类型更新为def do_this (a,b,c) puts 1.to_s, 2.to_s,3.to_s if a == 4 do_this(1,2,3) end end do_this(4,5,6)并添加List<StaffHierarchySearchViewModel>它似乎按预期工作。

return results.ToList();

}

将LINQ填充的ViewModel从业务逻辑层返回到Controller - MVC

2 个答案: