Question

I rewrite again my question, I didn’t expose it in the right way, sorry.

I have this SQL query:

SELECT T1.*, T2.documentNumber
FROM TABLE1 T1      
LEFT JOIN TABLE2 T2 ON      
    T2.documentNumber = (
        SELECT TOP 1 documentNumber         
        FROM TABLE2  
        WHERE description = T1.description)                                     
WHERE T1.color = 'RED';

I need to retrieve all the rows in T1 filtered by color with the corresponding T2.documentNumber value, but unique T1 rows, I mean, a relation 1 to 1 with T2.

T1 and T2 are related through description column. Because description is not unique in t2, this table can contain N rows with the same description, since I want only 1 row as result for each T1 row, I get the top 1 filtering by the unique column (documentNumber).

This query works fine for me, want I need to know is the equivalent for Linq-to-SQL, I tried for several hours but without success. Could please somebody help me?

Answer 1

Try

var result = table1.Where(t1 => t1.color == "RED")
                   .GroupJoin(table2,
                              t1 => t1.description,
                              t2 => t2.description,
                              (t1,g) => new {
                                              T1 = t1,
                                              DocumentNumber = g.FirstOrDefault()
                                             });

Mandatory 101 link: http://code.msdn.microsoft.com/101-LINQ-Samples-3fb9811b should help deal with these sort of queries….