如何按ICollection的屬性排序？

Question

我試圖找出對模型參數的ICollection的顯示或LINQ調用。 具體來說，這是我的PurchReq （采購申請）模型：

public enum FiscalYear
{
    [Display(Name="2013")]
    LastYear,
    [Display(Name="2014")]
    ThisYear,
    [Display(Name="2015")]
    NextYear
}

public class PurchReq
{
    [Key]
    public int PurchReqID { get; set; }
    [Display(Name="Fiscal Year")]
    public FiscalYear FiscalYear { get; set; }
    //[ForeignKey("Project")]
    //public int ProjectID { get; set; }
    [Required]
    [Display(Name="Purchase Requisition Number")]
    public string PurchReqNum { get; set; }
    public string GLCode { get; set; }
    public string Fund { get; set; }
    public string Division { get; set; }
    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
    [Display(Name = "Purch Req Created")]
    public DateTime? DateCreated { get; set; }
    [DataType(DataType.Date)]
    [DisplayFormat(DataFormatString = "{0:yyyy-MM-dd}", ApplyFormatInEditMode = true)]
    [Display(Name = "Purch Req Submitted")]
    public DateTime? DateSubmitted { get; set; }

    //many projects to many purchReqs
    //public virtual Project Project { get; set; }
    public virtual ICollection<Project> Projects { get; set; }

    public PurchReq()
    {
        DateCreated = System.DateTime.Now;
        Projects = new HashSet<Project>();
    }

這是我的PurchReqController用於索引方法：

  var purchReqs = from p in db.PurchReqs
                        select p;

        if (!string.IsNullOrEmpty(searchString))
        {
            purchReqs = purchReqs.Where(s => s.Projects.Any(item => item.Vendor.VendorName.Contains(searchString)));
        }
        switch (sortOrder)
        {
            case "ProjectName_desc":;
                purchReqs = purchReqs.OrderByDescending(s => s.Projects);
                    //Any(item => item.Vendor.VendorName).ThenBy(n => n.Project.Description));
                break;
            case "PurchReqNum_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.PurchReqNum);
                break;
            case "PurchReqNum_asc":
                purchReqs = purchReqs.OrderBy(s => s.PurchReqNum);
                break;
            case "FiscalYear_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.FiscalYear);
                break;
            case "FiscalYear_asc":
                purchReqs = purchReqs.OrderBy(s => s.FiscalYear);
                break;
            case "GLCode_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.GLCode);
                break;
            case "GLCode_asc":
                 purchReqs = purchReqs.OrderBy(s => s.GLCode);
                break;
            case "Fund_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.Fund);
                break;
            case "Fund_asc":
                purchReqs = purchReqs.OrderBy(s => s.Fund);
                break;
            case "Division_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.Division);
                break;
            case "Division_asc":
                purchReqs = purchReqs.OrderBy(s => s.Division);
                break;
            case "DateCreated_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.DateCreated);
                break;
            case "DateCreated_asc":
                purchReqs = purchReqs.OrderBy(s => s.DateCreated);
                break;
            case "DateSubmitted_desc":
                purchReqs = purchReqs.OrderByDescending(s => s.DateSubmitted);
                break;
            case "DateSubmitted_asc":
                purchReqs = purchReqs.OrderBy(s => s.DateSubmitted);
                break;
            default:
                purchReqs = purchReqs.OrderBy(s => s.Projects);
                //purchReqs = purchReqs.OrderBy(s => s.Projects.Any(item => item.Vendor.VendorName)).ThenBy(n => n.Project.Description);
                break;
        }
        return View(purchReqs);

上面的控制器拋出DbSort錯誤，因為它無法對ICollection項目進行排序，這是可以理解的。 我需要按Projects.Project.Vendor.VendorName對集合進行排序。 這最初在PurchReq to Project為多對一時起作用，但最近更改為多對多。 任何建議和幫助將不勝感激。

Answer 1

嘗試這個：

purchReqs = purchReqs.OrderBy(pr => pr.Projects.Count > 0 ? pr.Projects.First().Vendor.VendorName : "")
                     .ThenBy (pr => pr.Projects.Count > 0 ? pr.Projects.First().Description       : "");

在這里，我們使用First代替Any ； 它為我們提供了一些合適的元素（當然，這無關緊要，但是Any只是給我們一個布爾值，沒有其他讓我們選擇半隨機值的特定條件）。

我認為，在C＃6中，您可以使用以null傳播的成員訪問運算符執行以下操作：

purchReqs = purchReqs.OrderBy(pr => pr.Projects.FirstOrDefault()?.Vendor?.VendorName)
                     .ThenBy (pr => pr.Projects.FirstOrDefault()?.Description);

無論哪種方式，假定Project具有Description屬性，兩個排序調用都使用相同的結構。

Answer 2

我知道我對這個線程太遲了，並且不是MVC的專家，但是據我了解的關於排序集合的知識，它的工作原理是采用一個值並將其與同一列中的另一個值進行比較。 基本上，您需要從所需集合中選擇一個字段並將其提供給OrderBy lambda。

盡可能簡單，如下所示：

IQueryable purchReq = context.PurchReq.OrderBy(p => p.Projects.Select(pj => pj.Project).FirstOrDefault().Select(v => v.Vendor.VendorName).FirstOrDefault());

如果Project與供應商之間也存在1對n的關系，請替換

Select(v => v.Vendor.VendorName);

通過

Select(v => v.Vendor).FirstOrDefault().VendorName

希望這可以幫助。