linq如何从var获取值
如何从以下LINQ查询中获取单个值?(我想获取seapExpireDate、seapExpireMonth和seapExpireYear的值。)linq如何从var获取值,linq,c#-4.0,Linq,C# 4.0,如何从以下LINQ查询中获取单个值?(我想获取seapExpireDate、seapExpireMonth和seapExpireYear的值。) 我假设您希望从具有最高(最后一个)的元素中获取seapExpireDate、seapExpireMonth和seapExpireYear。然后您可以在此日期前订购: var latest = (from d in db.CT_Decals where d.TankID == decal.TankID && d.
我假设您希望从具有最高(最后一个)的元素中获取
seapExpireDate
、seapExpireMonth
和seapExpireYear
。然后您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;
做与Tim相同的假设,你也可以
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;
您将在“result”变量中获得所需的“CT_贴花”类型的对象,以便访问它的任何属性var q=from r in tab1.dictenaries
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;
}
选择新的{
r、 英语,
r、 法语的
};
列表sml=新列表();
int启动=10;
整数结束=20;
int-cntr=0;
foreach(q中的var verObj)
{
如果(cntr>=开始和结束(&cntr)
{
打破
}
cntr=cntr+1;
}
在Tim和Dipin的基础上,当查询没有产生任何结果时,First()
方法会抛出一个InvalidOperationException
要么用try/catch块将其包围
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!}
或者您可以使用FirstOrDefault()
,当查询不产生匹配项时,它将返回空引用
//... Example from above
}).FirstOrDefault();
// check for null-reference
if(latest != null)
var decalExpireDate = latest.DecalExpireDate;
var decalExpireMonth = latest.DecalExpireMonth;
var decalExpireYear = latest.DecalExpireYear;
}
第三种可能是使用take(1)
您已经在访问
decadexpiredate
,是吗?也许我当时写错了查询。我只带回了decadeExpireDate,但我想带回所有三个值……对不起,@user,我假设Max
将返回所有三个字段。我更新了。谢谢,正是我想要的。那么,我是否需要执行var variableName=wantedValue来获取单个值?@user1202606:您还可以编写DateTime-deafiredate=latest.deafiredate代码>如果这真的是一个日期时间。但因为我不确定是否使用了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查询通常返回一个IEnumerable
,这是一个元素序列(多个)。我取了序列的第一个元素(),该元素按日期变量降序*排列。因此,它是最后一个元素。
//... Example from above
}).FirstOrDefault();
// check for null-reference
if(latest != null)
var decalExpireDate = latest.DecalExpireDate;
var decalExpireMonth = latest.DecalExpireMonth;
var decalExpireYear = latest.DecalExpireYear;
}
//... 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;
}