linq如何从变量中获取值

如何从以下LINQ查询中获取各个值？（我想要得到DecalExpireDate，DecalExpireMonth和DecalExpireYear值）。linq如何从变量中获取值

var previousExpirationDate = (from d in db.CT_Decals 
           where d.TankID == decal.TankID 
           && d.DecalStatus == "Approved" 
           select new 
           { 
            d.DecalExpireDate, 
            d.DecalExpireMonth, 
            d.DecalExpireYear 
           }).Max(d => d.DecalExpireDate);

来源

2012-07-06 user1202606

第一要素你已经访问'DecalExpireDate'，不是吗？ – 2012-07-06 21:32:46

也许我正在写错误的查询。我只是带回DecalExpireDate，但我想要带回所有三个值...... – user1202606 2012-07-06 21:34:49

对不起，@user，我认为'Max'会返回所有三个字段。我更新了[我的回答]（http://stackoverflow.com/a/11368703/480799）。 – 2012-07-07 15:42:15

我假设你想从最高（最后）DecalExpireDate元素得到了DecalExpireDate，DecalExpireMonth和DecalExpireYear。然后，你可以在此日期前订购：

var latest = (from d in db.CT_Decals 
      where d.TankID == decal.TankID && d.DecalStatus == "Approved" 
      orderby d.DecalExpireDate descending 
      select new 
      { 
       d.DecalExpireDate, 
       d.DecalExpireMonth, 
       d.DecalExpireYear 
       }).First(); 
var decalExpireDate = latest.DecalExpireDate; 
var decalExpireMonth = latest.DecalExpireMonth; 
var decalExpireYear = latest.DecalExpireYear;

来源

2012-07-06 21:37:24

谢谢，正是我想要的。那么，我需要做var variableName = wantedValue，来获取单个值吗？ – user1202606 2012-07-06 21:43:10

@ user1202606：您也可以编写'DateTime decalExpireDate = latest.DecalExpireDate;'如果这真的是DateTime。但是因为我不确定我是否使用了'var'，它是实际类型的占位符。您需要选择一个元素来访问变量，LINQ查询通常会返回一个“IEnumerable ”这是一个元素序列（多个）。我将第一个元素（[First（）']（http://msdn.microsoft.com/zh-cn/library/system.linq.enumerable.first.aspx））排序为**由日期变量降序***。因此它是最后一个元素。 – 2012-07-06 21:46:05

作出同样的假设，蒂姆，你也可以用

var result = db.CT_Decals.OrderByDescending(d => d.DecalExpireDate).First(d => d.TankID == decal.TankID && d.DecalStatus == "Approved"); 

var expireDate = result.DecalExpireDate; 
var expireMonth = result.DecalExpireMonth; 
var expireYear = result.DecalExpireYear;

去你将有类型的“结果”变量所需的对象“CT_Decals”所以访问它

来源

2012-07-06 21:57:07

var q = from r in tab1.dictenaries 
        select new { 
         r.ENGLISH, 
         r.FRENCH 
        }; 

      List<SomeClass> sml = new List<SomeClass>(); 

      int starting = 10; 
      int ending = 20; 
      int cntr = 0; 
      foreach(var verObj in q) 
      { 
       if (cntr >= starting && cntr <= ending) 
       { 
        SomeClass sm1 = new SomeClass(); 
        sm1.ENGLISH = verObj.ENGLISH.ToString(); 
        sm1.FRENCH = verObj.FRENCH.ToString(); 
        sml.Add(sm1); 
       } 
       else if(cntr >ending) 
       { 
        break; 
       } 
       cntr = cntr + 1; 
      }

来源

2013-08-12 12:02:47 user2674838

添和Dipin构建财物时，First()方法不幸引发InvalidOperationException查询的时候不会产生任何结果。

要么你用try/catch块

try{ 
    var latest = (from d in db.CT_Decals 
       where d.TankID == decal.TankID && d.DecalStatus == "Approved" 
       orderby d.DecalExpireDate descending 
       select new 
       { 
        d.DecalExpireDate, 
        d.DecalExpireMonth, 
        d.DecalExpireYear 
        }).First(); 
    var decalExpireDate = latest.DecalExpireDate; 
    var decalExpireMonth = latest.DecalExpireMonth; 
    var decalExpireYear = latest.DecalExpireYear; 
} 
catch(InvalidOperationException ex){ // tell no Result!}

围绕着它，或者你可以使用FirstOrDefault()当查询产生不匹配，这将返回一个空引用。

//... Example from above 

}).FirstOrDefault(); 

// check for null-reference 
if(latest != null) 
    var decalExpireDate = latest.DecalExpireDate; 
    var decalExpireMonth = latest.DecalExpireMonth; 
    var decalExpireYear = latest.DecalExpireYear; 
}

第三种可能性是采取使用Take(1)

//... Example from above 

}).Take(1).ToList(); // returns an empty list if no match 

// check whether something was returned 
if(latest.Any()) 
    var decalExpireDate = latest[0].DecalExpireDate; 
    var decalExpireMonth = latest[0].DecalExpireMonth; 
    var decalExpireYear = latest[0].DecalExpireYear; 
}

来源

2016-02-18 07:54:06

linq如何从变量中获取值

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