LINQ-Join tables on nullable columns
how to JOIN tables on nullable columns?
I have following LINQ-query, RMA.fiCharge
can be NULL:
Dim query = From charge In Services.dsERP.ERP_Charge _
Join rma In Services.dsRMA.RMA _
On charge.idCharge Equals rma.fiCharge _
Where rma.IMEI = imei
Select charge.idCharge
I get a "Conversion from type 'DBNull' to type 'Integer' is not valid" in query.ToArray()
:
Dim filter = _
String.Format(Services.dsERP.ERP_Charge.idChargeColumn.ColumnName & " IN({0})", String.Join(",", query.ToArray开发者_Go百科))
So i could append a WHERE RMA.fiCharge IS NOT NULL
in the query. But how to do that in LINQ or is there another option?
Thank you in advance.
Solution:
The problem was that the DataSet does not support Nullable-Types but generates an InvalidCastException if you query any NULL-Values on an integer-column(thanks Martinho).
The modified LINQ-query from dahlbyk works with little modification. The DataSet generates a boolean-property for every column with AllowDbNull=True, in this case IsfiChargeNull
.
Dim query = From charge In Services.dsERP.ERP_Charge _
Join rma In (From rma In Services.dsRMA.RMA _
Where Not rma.IsfiChargeNull
Select rma)
On charge.idCharge Equals rma.fiCharge _
Where rma.IMEI = imei
Select charge.idCharge
Have you tried adding the null check to your where
clause?
Dim query = From charge In Services.dsERP.ERP_Charge _
Join rma In Services.dsRMA.RMA _
On charge.idCharge Equals rma.fiCharge _
Where rma.fiCharge <> Nothing AndAlso rma.IMEI = imei
Select charge.idCharge
If that doesn't work, you could try something like this:
Dim query = From charge In Services.dsERP.ERP_Charge _
Join rma In (From rma in Services.dsRMA.RMA _
Where rma.fiCharge IsNot Nothing
Select rma)
On charge.idCharge Equals rma.fiCharge _
Where rma.IMEI = imei
Select charge.idCharge
While you can use LINQ to Datasets to solve this issue, you might find better performance using the predefined DataRelations instead of ad-hoc joins. See http://msdn.microsoft.com/en-us/library/dbwcse3d.aspx for information about data relations.
If you do use LINQ to Datasets, you might want to check out our free bonus chapter 14 on them at http://www.manning.com/marguerie/.
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