我附加了一个简单的LINQ查询。 我想弄清楚是否有更好更有效的方法来拉动这三个字段(Field1,Field2,Field3),如下面的LINQ查询中所述。
from currentCons in ActiveConnections
join accounts in Accounts on currentCons.New_AccountId equals accounts.AccountId
let Field1 =(from holder in MapHolders
join entity in Entities on stringmap.ObjectTypeCode equals entity.ObjectTypeCode
where entity.Name == "New_Connection"
where holder.AttributeName == "New_Data"
where holder.AttributeValue == currentCons.New_DATA_Val
select holder.Value)
let Field2=(from holder in MapHolders
join entity in Entities on stringmap.ObjectTypeCode equals entity.ObjectTypeCode
where entity.Name == "New_Connection"
where holder.AttributeName == "New_Type"
where holder.AttributeValue == currentCons.New_Type
select holder.Value)
let Field3=(from holder in MapHolders
join entity in Entities on stringmap.ObjectTypeCode equals entity.ObjectTypeCode
where entity.Name == "New_Connection"
where holder.AttributeName == "New_EntryPoint"
where holder.AttributeValue == currentCons.New_EntryPoint
select holder.Value)
where currentCons.ModifiedOn >= Convert.ToDateTime("1/1/2011")
where currentCons.ModifiedOn <= Convert.ToDateTime("5/5/2012")
select new
{
conId = currentCons.ConnectionId,
ConName = currentCons.name,
TypeId = currentCons.Type,
AccountId = currentCons.AccountId,
OId = currentCons.OwnerId,
BandwidthId = currentCons.Bandwidth,
EntryPointId = currentCons.EntryPoint,
Cap = Field1 ,
Dir=Field2,
EP=Field3,
ModifiedOn = currentCons.ModifiedOn
}
我知道另一种方法是直接放入Select Block。什么是有效的方法呢?
任何指针都表示赞赏。
感谢。
答案 0 :(得分:1)
var fromDate = new DateTime(2011,1,1);
var toDatePlusOneDay = new DateTime(2012,5,5).AddDays(1); // add one day to ensure
var result = from currentCons in ActiveConnections
join accounts in Accounts on currentCons.New_AccountId equals accounts.AccountId
where currentCons.ModifiedOn >= fromDate
where currentCons.ModifiedOn < toDatePlusOneDay
from holder in MapHolders
where (holder.AttributeName == "New_Data" && holder.AttributeValue == currentCons.New_DATA_Val) || (holder.AttributeName == "New_Type" && holder.AttributeValue == currentCons.New_Type) || (holder.AttributeName == "New_EntryPoint" && holder.AttributeValue == currentCons.New_EntryPoint)
select new
{
conId = currentCons.ConnectionId,
ConName = currentCons.name,
TypeId = currentCons.Type,
AccountId = currentCons.AccountId,
OId = currentCons.OwnerId,
BandwidthId = currentCons.Bandwidth,
EntryPointId = currentCons.EntryPoint,
ModifiedOn = currentCons.ModifiedOn,
Cap = (holder.AttributeValue == currentCons.New_DATA_Val) ? holder.Value : null,
Dir = (holder.AttributeValue == currentCons.New_Type) ? holder.Value : null,
EP = (holder.AttributeValue == currentCons.New_EntryPoint) ? holder.Value : null
}
我删除了以下内容,因为它未在任何结果中使用
join entity in Entities on stringmap.ObjectTypeCode equals entity.ObjectTypeCode
where entity.Name == "New_Connection"
另外请检查Cap / Dir / EP是否可以为空