Left outer join null using VB.NET and LINQ

I've got what I think is a working left outer join LINQ query, but I'm having problems with the select because of null values in the right hand side of the join. Here is what I have so far

 Dim Os = From e In oExcel
        Group Join c In oClassIndexS On c.tClassCode Equals Mid(e.ClassCode, 1, 4)
        Into right1 = Group _
        From c In right1.DefaultIfEmpty

I want to return all of e and one column from c called tClassCode. I was wondering what the syntax would be. As you can see, I'm using VB.NET.

Update...

Here is the query doing join where I get the error:

_message = "Object reference not set to an instance of an object."

 Dim Os = From e In oExcel
             Group Join c In oClassIndexS On c.tClassCode Equals Mid(e.ClassCode, 1, 4)
             Into right1 = Group _
             From c In right1.DefaultIfEmpty
        Select e, c.tClassCode

If I remove the c.tClassCode from the select, the query runs withou开发者_运维问答t error. So I thought perhaps I needed to do a select new, but I don't think I was doing that correctly either.

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EDIT: you need to check c for null, specifically the c after your grouping. See my updates below.

You need to do a null check on tClassCode c in your select statement. What type is tClassCode? You should be able to do a null check on the value c and if it's null cast a nullable of the respective type and returned it, otherwise return the actual value.

Since I am not sure what tClassCode is let's assume it's an integer, in which case the cast would be to a nullable integer (Integer?). With that in mind your select statement, to be added at the end of what you have so far, should resemble:

Since tClassCode is a string your code would resemble:

Select _
    e, _
    Code = If(c Is Nothing, Nothing, c.tClassCode)

Depending on what you need to do if c is null you could return String.Empty instead of Nothing:

Select _
    e, _
    Code = If(c Is Nothing, String.Empty, c.tClassCode)

Of course you are free to further expand the selection of "e" to project its specific columns by name.

The important thing to realize is that you must check c for null before using any of its properties since it might be null depending on the left outer join result for a particular result (row). Back to my earlier example, if you had another field named Priority that was an integer you would cast against a nullable:

Select _
    e, _
    Priority = If(c Is Nothing, CType(Nothing, Integer?), c.Priority)

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Well, I got it working... At least I get results without errors. Thanks for the help... Here it is.

 Dim Os = From e In oExcel
                 Group Join c In oClassIndexS On c.tClassCode Equals Mid(e.ClassCode, 1, 4)
                 Into right1 = Group _
                 From jo In right1.DefaultIfEmpty()
        Select New With {.CivilServiceTitle = e.CivilServiceTitle, .Code = If(jo Is Nothing, Nothing, jo.tClassCode)}