Question

How to do an update in LINQ to Objects. Trying convert SQL to Linq

Quality
        (
          TransactionID int,
          Quantity float,
          MaterialID int,
          ProductID int,
          ParameterID int,
          ParameterValue float,
          TotalTonnes float
        )

How to convert below SQL to linq:

UPDATE  Q1
            SET     TotalTonnes = ( SELECT  SUM(Quantity)
                                    FROM    @Quality Q2
                                    WHERE   Q1.ParameterID = Q2.ParameterID
                                            AND ( ( Q1.MaterialID = Q2.MaterialID )
                                                  OR ( Q1.MaterialID IS NULL
                                                       AND Q2.MaterialID IS NULL
                                                     )
                                                )
                                            AND ( ( Q1.ProductID = Q2.ProductID )
                                                  OR ( Q1.ProductID IS NULL
                                                       AND Q2.ProductID IS NULL
                                                     )
                                                )
                                  )
            FROM    @Quality Q1

Thanks

Answer 1

Well, I would do updates imperatively. Something like this:

foreach (var q1 in Q1)
{
    q1.TotalTonnes = (from q2 in Q2
                      where q1.ParameterID == q2.ParameterID
                        && q1.MaterialID == q2.MaterialID
                        && q1.ProductID == q2.ProductID
                      select q2.Quantity).Sum();
}

Note that the double null checks aren’t required because of the way null comparisons are handled in C#. (i.e. (null == null) is true)