Linq left join with multiple columns and default values [duplicate] - linq

Question

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Closed 10 years ago.
I am fairly new to linq and I need to join two tables with the following requirements:
Should left join t1 and t2.
If t2 is empty then the query should not fail - should use default values.
My query:
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
};
Can someone correct this?

Answer 1

This works in Linqpad as a C# program.
Basically your join syntax needed tweaking (see this), and you needed to take into account when there was nothing to join to for "t2" (so we do a null check and use 0 when null, otherwise t2.Amount, etc)
I created some dummy data so you can play around.
See http://codingsense.wordpress.com/2009/03/08/left-join-right-join-using-linq/ for another example.
I hope it does what you want it to do.
Thanks,
Dominique
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; }
}

Answer 2

Thanks for your input. None of the answers did quite what I wanted, but I managed to get my original code working:
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
};
If you have any comments or improvements on this let me know, thanks.

Answer 3

According to this, you are looking for something like (this is untested, but hopefully leads you on the right track):
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
};
Notice the .DefaultIfEmpty(), this satisfies: "If t2 is empty then the query should not fail - should use default values."