C# 有效操作上的NullReferenceException
我需要从一个查询中获取我的ID（键入C# 有效操作上的NullReferenceException,c#,linq,entity-framework,C#,Linq,Entity Framework,我需要从一个查询中获取我的ID（键入Guid）： var firstQuery = from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0) join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID select new { ContPrice = conts.Price, Roo
Guidvar firstQuery =
from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
select new
{
ContPrice = conts.Price,
RoomPrice = rooms.Price
IDs = rooms.ID
};
foreach (var t in firstQuery)
{
t.RoomPrice = t.ContPrice;
}
var myIDs = firstQuery.Select(cr => cr.IDs).ToList();
var secondQuery =
from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
where !myIDs.Contains(rooms.fldID)
join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
select new
{
RoomPrice = conts.fldPrice,
IDs = rooms.ID
};
var myIDs = firstQuery.Select(cr => cr.IDs).ToList();
对象引用未设置为对象的实例
它似乎与第二个查询有关，因为当我把第二个查询转换成一个单独的方法并将ID传递给它时，所有的东西都工作得很好，但是我不明白为什么它应该考虑变量初始化后写的一些查询。 整个守则是：
var calcDate = DateTime.Now.AddDays(-1);
var firstQuery =
from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
where conts.date == calcDate
select new
{
ContPrice = conts.Price,
RoomPrice = rooms.Price
IDs = rooms.ID
};
foreach (var t in firstQuery)
{
t.RoomPrice = t.ContPrice;
}
var myIDs = firstQuery.Select(cr => cr.IDs).ToList();
var secondQuery =
from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
where !myIDs.Contains(rooms.fldID)
join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
where conts.date == calcDate && conts.Code = "01"
select new
{
RoomPrice = conts.fldPrice,
IDs = rooms.ID
};
foreach (var t in secondQuery)
{
ContPrice = Conts.Price,
RoomPrice = Rooms.Price
}
myEntityContext.SaveChanges();
我假设
var FirstQuery内容。var FirstQuery = (from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
join Conts in myEntityContextt.Cont on rooms.ID equals Conts.ItemID
select new
{
RoomPrice = Conts.fldPrice,
IDs = rooms.ID
}).ToList();
如果此行失败，则myEntityContext.Mark或myEntityContext.Cont可能是空对象IDs IDs=rooms.ID可能获得空值 尝试添加以下内容： var myIDs=FirstQuery.ToList（）.Select（Cr=>Cr.IDs.ToList（） 嗯，堆栈跟踪很有用：我假设您发布的代码位于
DoCalc（）var myIDs = firstQuery.Select(cr => cr.IDs).ToList();
NullReferenceExceptionfirstQueryfirstQuery.Select（cr=>cr.id）ArgumentNullExceptionNullReferenceException而且，你的代码不应该运行 例如，在下面的部分中，您应该会得到一个编译时错误：
foreach (var t in firstQuery)
{
t.RoomPrice = t.ContPrice;
}
foreach (var t in secondQuery)
{
ContPrice = Conts.Price,
RoomPrice = Rooms.Price
}
最有可能发生什么 您在
myEntityContext.RoommyEntityContext.Contnullvar myIDs=new List（）；
var myIDs = new List<int>();
if( firstQuery.Count() > 0)
myIds = firstQuery.Select(cr => cr.IDs).ToList();
if（firstQuery.Count（）>0）
myIds=firstQuery.Select（cr=>cr.IDs.ToList（）；
public class QueryResult
{
public decimal ContPrice; //whatever your types are
public decimal RoomPrice;
public int IDs;
}
var firstQuery =
from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
where conts.date == calcDate
select new QueryResult
{
ContPrice = conts.Price,
RoomPrice = rooms.Price,
IDs = rooms.ID
};
var firstQueryResult = firstQuery.ToList();
foreach (var t in firstQueryResult)
{
t.RoomPrice = t.ContPrice;
}
conts.Code.Equals("01")
var roomsOpenQuery = myEntityContext.Room.Where(t => t.fldClosed == 0);
var roomsOpenQueryResolved = roomsOpenQuery.ToList();
var contQuery = myEntityContext.Cont
.Where(t => roomsOpenQueryResolved.Any(r => r.ID == t.ItemID))
.Where(x => x.date == calcDate);
var availableRooms =
contQuery
.Join(roomsOpenQueryResolved,
c => c.ItemID,
r => r.ID,
(c, r) => new AvailableRoom()
{
ContPrice = c.Price,
RoomPrice = r.Price,
IDs = c.ItemID
})
.ToList();
//Price Adjustment etc...
为什么没有任何评论就投了反对票？也许一个完整的框架可以help@MaryamArshi在出现异常情况时，您确实需要向我们提供。否则我们帮不了你。我怀疑例外情况是否发生在您指定的行中。还有一个堆栈跟踪字符串，可以从VisualStudio中抛出的
异常中获取。只需复制并添加到您的帖子中。@MaryamArshi您仍然应该发布