Question

Q:

I have two queries each one return a DataTable. I wanna to return another DaTaTable as a result of(What exist in the first DataTable AND Not Exist(NOT IN) the second DataTable).

My queries:

EDIT : I make it general:

1-DT1:

DataTable dt1 = cc1assiscrsevalDAL.GetAll(int.Parse(Session["course_prof"].ToString()), 0);

2-DT2:

DataTable dt2 = cc1assiscrsevalDAL.GetConfirmedEval(int.Parse(Session["course_prof"].ToString()));

Note:batch_no,crsnum,lect_code are the composite primary key

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What is the best way to do that?(wise performance).
I wanna also to do that with LINQ.(if possible).

Answer 1

var dt = dt1.AsEnumerable().Except(dt2.AsEnumerable(), new CustomDataRowEqualityComparer()).CopyToDataTable();

    public class CustomDataRowEqualityComparer: IEqualityComparer<DataRow>
        {

            public bool Equals(DataRow x, DataRow y)
            {
                return ((int)x["crsnum"]) == ((int)y["crsnum"])
                    && ((int)x["crsnum_e"]) == ((int)y["crsnum_e"])
                        && ((int)x["crstteng"]) == ((int)y["crstteng"]);
            }

            public int GetHashCode(DataRow obj)
            {
                return ((int)obj["crsnum"]) ^ ((int)obj["crsnum_e"]) ^ ((int)obj["crstteng"]) ;
            }
        }

There is an extension method in the linq called Except which solves your problem but we need to create a separate class for that which i have done in the above code.