Question

Hello i have a problem joining tables when i have null values in a record.

There are 2 dataTables:

1. Workers: (workerID, workerName, workerAdress)
2. Transactions: (transactionID, transactioinValue, worker1, worker2), where worker 2 is optional so it can contain null values.

So i started code like this:

var record = from transaction in dtTransactions.AsEnumerable()
    join worker1 in dtWorkers.AsEnumerable() on (int)transactions["worker1"] equals (int)worker1["workerID"]
    join worker2 in dtWorkers.AsEnumerable() on (int)transactions["worker2"] equals (int)worker2["workerID"]
    select new
    {
     ID = (int)transactions["transactionID"],
     Name1= worker1["workerName"],
     Name2= worker2["workerName"]
    };

So it all works fine if worker2 isn’t null, but when i have a null value it could not be joined. Can someone help me with this problem, i would like to have a result record without a worker2 name if it’s null in dataTable.

Is it possible?

Answer 1

you need to do a left join like this;

var record = from transaction in dtTransactions.AsEnumerable()
                     join worker1 in dtWorkers.AsEnumerable() on (int)transactions["worker1"] equals (int)worker1["workerID"]
                     join worker2 in dtWorkers.AsEnumerable() on (int)transactions["worker2"] equals (int)worker2["workerID"] into w2
                     from wrk in w2.DefaultIfEmpty()
                     select new
                     {
                         ID = (int)transactions["transactionID"],
                         Name1= worker1["workerName"],
                         Name2= wrk["workerName"]
                     };

Secondly, is there any reason why you’re not specifying the object properties like this;

                var record = from transaction in dtTransactions.AsEnumerable()
                 join worker1 in dtWorkers.AsEnumerable() on (int)transactions.worker1 equals (int)worker1.workerID
                 join worker2 in dtWorkers.AsEnumerable() on (int)transactions.worker2 equals (int)worker2.workerID into w2
                 from wrk in w2.DefaultIfEmpty()
                 select new
                 {
                     ID = (int)transactions.transactionID,
                     Name1= worker1.workerName,
                     Name2= wrk != null ? wrk.workerName : ""
                 };

Note the removal of the square brackets