我对linq很新，我需要加入两个具有以下要求的表：
应该加入t1和t2。
如果t2为空，则查询不应失败 - 应使用默认值。
我的查询：
var final = from t1 in saDist.AsEnumerable()
from t2 in sapGrouped.AsEnumerable()
where
t1.Supplier.Id == t2.Supplier.Id && t1.VatRate == t2.VatRate
select
new
{
t1.Supplier,
Amount = t1.Amount - t2.Amount,
Advance = t1.Advance - t2.Advance,
Balance = t1.Balance - t2.Balance,
t1.VatRate
};
有人可以纠正这个吗？
答案 0 :(得分：2)
这适用于Linqpad作为C＃程序。
基本上你的连接语法需要调整（参见this），你需要考虑什么时候没有什么可以加入“t2”（所以我们做空检查并在null时使用0，否则t2.Amount等）
我创建了一些虚拟数据，因此你可以玩。
有关其他示例，请参阅http://codingsense.wordpress.com/2009/03/08/left-join-right-join-using-linq/。
我希望它可以做你想做的事。
谢谢， 多米尼克
public class A
{
void Main()
{
Distributor dist1 = new Distributor() { SupplierID = 1, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "A", DeptSupplierID = 1 };
Distributor dist2 = new Distributor() { SupplierID = 2, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "B", DeptSupplierID = 1 };
Distributor dist3 = new Distributor() { SupplierID = 3, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "C", DeptSupplierID = 1 };
Distributor dist4 = new Distributor() { SupplierID = 4, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "D", DeptSupplierID = 2 };
Distributor dist5 = new Distributor() { SupplierID = 5, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "E", DeptSupplierID = 2 };
Distributor dist6 = new Distributor() { SupplierID = 6, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "F", DeptSupplierID = 2 };
Distributor dist7 = new Distributor() { SupplierID = 7, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "G", DeptSupplierID = 6 };
Distributor dist8 = new Distributor() { SupplierID = 8, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "H", DeptSupplierID = 3 };
Distributor dist9 = new Distributor() { SupplierID = 9, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "I", DeptSupplierID = 3 };
Distributor dist10 = new Distributor() { SupplierID = 10, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "J", DeptSupplierID = 7 };
Distributor dist11 = new Distributor() { SupplierID = 11, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "K", DeptSupplierID = 7 };
Distributor dist12 = new Distributor() { SupplierID = 12, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "L", DeptSupplierID = 5 };
SAPGroup Dept1 = new SAPGroup() { SupplierID = 1, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Development" };
SAPGroup Dept2 = new SAPGroup() { SupplierID = 2, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Testing" };
SAPGroup Dept3 = new SAPGroup() { SupplierID = 3, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Marketing" };
SAPGroup Dept4 = new SAPGroup() { SupplierID = 4, Amount = 3, Balance = 4, Advance = 3, VatRateID = 1, Name = "Support" };
List ListOfDistributors = new List();
ListOfDistributors.AddRange((new Distributor[] { dist1, dist2, dist3, dist4, dist5, dist6, dist7,
dist8, dist9, dist10, dist11, dist12 }));
List ListOfSAPGroup = new List();
ListOfSAPGroup.AddRange(new SAPGroup[] { Dept1, Dept2, Dept3, Dept4 });
var final = from t1 in ListOfDistributors
join t2 in ListOfSAPGroup
on new { t1.SupplierID, t1.VatRateID } equals new { t2.SupplierID, t2.VatRateID }
into JoinedDistAndGrouped
from t2 in JoinedDistAndGrouped.DefaultIfEmpty()
select new
{
Name1 = t1.Name,
Name2 = (t2 == null) ? "no name" : t2.Name,
SupplierID = t1.SupplierID,
Amount = t1.Amount - (t2 == null ? 0 : t2.Amount),
Advance = t1.Advance - (t2 == null ? 0 : t2.Advance),
Balance = t1.Advance - (t2 == null ? 0 : t2.Balance),
VatRateID = t1.VatRateID
};
final.Dump();
}
}
class Distributor
{
public string Name { get; set; }
public int SupplierID { get; set; }
public int VatRateID { get; set; }
public int DeptSupplierID { get; set; }
public int Amount { get; set; }
public int Advance { get; set; }
public int Balance { get; set; }
}
class SAPGroup
{
public int SupplierID { get; set; }
public int VatRateID { get; set; }
public string Name { get; set; }
public int Amount { get; set; }
public int Advance { get; set; }
public int Balance { get; set; }
}
public class Result
{
public string Name1 { get; set; }
public string Name2 { get; set; }
public int SupplierID { get; set; }
public int Amount { get; set; }
public int Advance { get; set; }
public int Balance { get; set; }
public int VatRateID { get; set; }
}
答案 1 :(得分：2)
感谢您的投入。没有一个答案符合我的要求，但我设法让原始代码正常工作：
var final = from t2 in saDist.AsEnumerable()
from t1 in sapGrouped.AsEnumerable().DefaultIfEmpty()
where
t1 == null || (t2.Supplier.Id == t1.Supplier.Id && t2.VatRate == t1.VatRate)
select
new
{
t2.Supplier,
Amount = t2.Amount - (t1 == null ? 0 : t1.Amount),
Advance = t2.Advance - (t1 == null ? 0 : t1.Advance),
Balance = t2.Balance - (t1 == null ? 0 : t1.Balance),
t2.VatRate
};
如果您对此有任何意见或改进，请告诉我，谢谢。
答案 2 :(得分：0)
根据this，您正在寻找类似的东西（这是未经测试的，但希望能引导您走上正轨）：
var final = from t1 in saDist.AsEnumerable()
join t2 in sapGrouped.AsEnumerable()
on t1.Supplier.Id equals t2.Supplier.Id
and t1.VatRate equals t2.VatRate into t1_t2 //not sure about this line
from t2 in t1_t2.DefaultIfEmpty()
{
t1.Supplier,
Amount = t1.Amount - t2.Amount,
Advance = t1.Advance - t2.Advance,
Balance = t1.Balance - t2.Balance,
t1.VatRate
};
注意.DefaultIfEmpty()，这满足：“如果t2为空，那么查询不应该失败 - 应该使用默认值。”