您如何按 ICollection 的属性进行排序

本文关键字：排序 属性 何按 ICollection | 更新日期: 2023-09-27 18:35:33

我正在尝试找出对模型参数ICollection的显示或LINQ调用。具体来说，这是我的PurchReq（采购申请）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>();
    }

这是我的索引方法的PurchReqController：

  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);

上面的控制器抛出 DbSort 错误，因为它无法对 ICollection 项目进行排序，这是可以理解的。我需要按 Projects.Project.Vendor.VendorName 对集合进行排序。这最初在 PurchReq to Project 是多对一时有效，但最近已更改为多对多。任何建议和帮助将不胜感激。

您如何按 ICollection 的属性进行排序

试试这个：

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

这里我们使用First而不是Any;它给了我们一些合适的元素（当然，这并不重要，但Any只是给了我们一个布尔值，没有其他特定的元素可以让我们半随机选择一个）。

在 C# 6 中，我认为您可以使用 null 传播成员访问运算符执行以下操作：

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

无论哪种方式，都对两个排序调用使用相同的结构，假设Project具有 Description 属性。

我知道我在这个线程上超级晚了，而且不是 MVC 方面的专家，但据我对排序集合的理解，它的工作原理是获取一个值并将其与同一列中的另一个值进行比较。基本上，您需要从所需的集合中选择一个字段并将其提供给 OrderBy lambda。

尽可能简单，它变得像这样：

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

如果项目与供应商也有 1 到 n 的关系，请替换

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

由

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

希望这有帮助。

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