LINQ Lambda 用于创建包含来自 3 个相关表的信息的列表

Question

我正在尝试使用 Receipt table 中的信息创建一个 ViewModel 列表，然后如果 Reason table 中存在相关信息，则检索最后插入的描述（ReceiptId 相关）并添加它（如果不存在只需将 null) 传递给 ViewModel 收据列表 (RejectDescription)。这是数据库模型：

Database Model

我尝试了很多方法来实现这一点，目前这是对我部分有效的代码，我说部分是因为在 RejectDescription 中保存 Reason.Description 如果它存在，否则只需传递 null 就可以了。

主要问题是当有很多 Reason.Description 时，它不会 return 并保存最后插入的一个（最近的，就是我要找的那个）。这是我的代码：

    [HttpPost]
    public ActionResult ReceiptList(string Keyword)
    {
        using (SEPRETEntities DBC = new SEPRETEntities())
        {
            long UserId = (long)Session["Id"];
            IEnumerable<Receipt> receipts = DBC.Receipts.Where(x => x.PersonId == UserId && x.Active == true).ToList();

            #region Search
            if (!string.IsNullOrEmpty(Keyword))
            {
                Keyword = Keyword.ToLower();

                receipts = receipts.Where(x => x.Person.Name.ToLower().Contains(Keyword) ||
                x.Person.MiddleName.ToLower().Contains(Keyword) ||
                x.Person.LastName.ToLower().Contains(Keyword) ||
                x.Person.Email.ToLower().Contains(Keyword) ||
                x.Person.Enrollment.ToLower().Contains(Keyword) ||
                x.Person.Career.ToLower().Contains(Keyword) ||
                x.Payment.Name.ToLower().Contains(Keyword) ||
                x.Payment.Price.ToString().ToLower().Contains(Keyword) ||
                x.Method.Name.ToLower().Contains(Keyword) ||
                x.Phase.Name.ToLower().Contains(Keyword) ||
                x.TimeCreated.ToString().ToLower().Contains(Keyword) ||
                x.Voucher.ToString().ToLower().Contains(Keyword)
                );
            }
            #endregion

            List<ReceiptVM> ReceiptList = receipts.Select(x => new ReceiptVM
            {
                Id = x.Id,
                PaymentId = x.PaymentId,
                Enrollment = x.Person.Enrollment,
                Career = x.Person.Career,
                PersonName = string.Concat(x.Person.Name, " ", x.Person.MiddleName, " ", x.Person.LastName),
                Email = x.Person.Email,
                PaymentName = x.Payment.Name,
                MethodName = x.Method.Name,
                Voucher = x.Voucher,
                Image = x.Image,
                PhaseId = x.Phase.Id,
                PriceFormatted = x.Payment.Price.ToString("C"),
                Active = x.Active,
                TimeCreatedFormatted = x.TimeCreated.ToString(),
                RejectDescription = x.Rejections.FirstOrDefault(y => y.ReasonId == y.Reason.Id)?.Reason.Description
            }).ToList();

            return PartialView("~/Views/Receipt/_SearchReceipt.cshtml", ReceiptList);
        }
    }

关于你的信息，我是 C# 的新手，ASP.NET MVC.Not 确定是否有更好的方法来实现这个或其他东西，非常感谢任何建议或技巧。

谢谢你，抱歉我的英语不好

Answer 1

您必须按 Id 排序拒绝原因，这将获取最近的原因，如下所示：

RejectDescription = x.Rejections.OrderByDescending(x=>x.Reason.Id).FirstOrDefault(y => y.ReasonId == y.Reason.Id)?.Reason.Description

或者您可以使用 LastOrDefault 获取最近的一个，如下所示： RejectDescription = x.Rejections.LastOrDefault(y => y.ReasonId == y.Reason.Id)?.Reason.Description

 List<ReceiptVM> ReceiptList = receipts.Select(x => new ReceiptVM
                {
                    Id = x.Id,
                    PaymentId = x.PaymentId,
                    Enrollment = x.Person.Enrollment,
                    Career = x.Person.Career,
                    PersonName = string.Concat(x.Person.Name, " ", x.Person.MiddleName, " ", x.Person.LastName),
                    Email = x.Person.Email,
                    PaymentName = x.Payment.Name,
                    MethodName = x.Method.Name,
                    Voucher = x.Voucher,
                    Image = x.Image,
                    PhaseId = x.Phase.Id,
                    PriceFormatted = x.Payment.Price.ToString("C"),
                    Active = x.Active,
                    TimeCreatedFormatted = x.TimeCreated.ToString(),
                    RejectDescription = x.Rejections.OrderByDescending(x=>x.Reason.Id).FirstOrDefault(y => y.ReasonId == y.Reason.Id)?.Reason.Description
                }).ToList();

LINQ Lambda 用于创建包含来自 3 个相关表的信息的列表

LINQ Lambda for create a list with info from 3 related tables

c#

linq

asp.net-mvc

linq-to-entities

entity-framework