Question

所以使用LINQ尝试比较数据库中的2个值并选择日期小于今天的一年...所以24/12/12之间的任何内容将选择24/1/13。

所以我有......

  var selectedObject =
            (from workstation in db.Work_Station
             join invoice in db.Invoices on workstation.id equals invoice.Site_Id
             where InvoiceDate < DateTime.Now.AddYears(-1)
             select workstation).Distinct().ToList();

这是产生一个列表，但它不正确。我一直在玩添加年，但似乎无法得到它.. 有人有主意吗？谢谢

编辑：嘿大家都感谢你的快速反应...我实际上犯了一个小错误，我想要返回一个发票日期大于一年的价值.....所以任何日期都是＆lt; = 24/1 / 12将被退回。我用过你的建议......

DateTime OneYearAgo = DateTime.Now.AddYears（-1）;

    var selectedObject  =
        (from workstation in db.Work_Station
         join invoice in db.Invoices on workstation.id equals invoice.Site_Id
          where InvoiceDate <= OneYearAgo
         select workstation).Distinct().ToList();

这会返回一些发票......其中一些发票在23/1/12之前，其中一些发票在之后。

我尝试更改到CurrentInvoiceDate＆gt; = OneYearAgo，它应该返回从现在到一年前的任何日期，但没有任何返回...我做错了什么？请指教......谢谢

Answer 1

提供您希望发票所属的日期范围：

  var beginDate = DateTime.Now.AddYears(-1);
  var endDate = DateTime.Now;
  var selectedObject =
            (from workstation in db.Work_Station
             join invoice in db.Invoices on workstation.id equals invoice.Site_Id
             where invoice.InvoiceDate >= beginDate &&
                   invoice.InvoiceDate <= endDate
             select workstation).Distinct().ToList();

Answer 2

您的查询符合您的文字说明。但两者都不符合您的样本数据。

您想要的是一年前日期大于或等于（不小于）的所有数据：

var selectedObject =
            (from workstation in db.Work_Station
             join invoice in db.Invoices on workstation.id equals invoice.Site_Id
             where InvoiceDate >= DateTime.Today.AddYears(-1)
             select workstation).Distinct().ToList();

如果您的发票可能在将来有日期，您还需要指定发票的日期小于或等于至今：

var selectedObject =
            (from workstation in db.Work_Station
             join invoice in db.Invoices on workstation.id equals invoice.Site_Id
             where InvoiceDate >= DateTime.Today.AddYears(-1)
                && InvoiceDate <= DateTime.Today
             select workstation).Distinct().ToList();

顺便说一句：您想使用DateTime.Today代替DateTime.Now 使用DateTime.Now不会从24/1/12返回没有时间或比现在早的时间的发票。

Answer 3

代码看起来像这样......

var selectedObject =
            (from workstation in db.Work_Station
             join invoice in db.Invoices on workstation.id equals invoice.Site_Id
             where InvoiceDate >= DateTime.Now.AddYears(-1) &&
                   InvoiceDate <= DateTime.Now
             select workstation).Distinct().ToList();

Answer 4

我会使用一些外部时态变量，以避免查询中的DateTime操作（有时C＃DateTime和SQL DateTime2不相处）。

DateTime timeNow = DateTime.Now;
DateTime timeToCompare = DateTime.Now.Subtract(new TimeSpan(365, 0, 0, 0)); ;
var selectedObject = (from workstation in db.Work_Station
                      join invoice in db.Invoices on workstation.id equals invoice.Site_Id
                      where InvoiceDate > timeToCompare
                      select workstation).Distinct().ToList();

看看它是否有帮助（我有很多问题以这种方式完成:)

编辑：如下所述，没有注意到比较实际上要比一年前更大。

选择A，其中A＆lt; LINQ中的B.

4 个答案: