Datatables, Except, c#

Question

I have two Datatables

Datatable A; //has a primany key ID
Datatable B; // has a primary key ID

I want the difference between A and B (A minus B). When using except operator in C#, on what parameter does except function? I want the difference between A and B based on the primary key.

Answer 1

Here'c complete code. The rows are compared by Id column (you can see it in RowsComparer's Equals method).

namespace SO
{
    class Program
    {
        static void Main(string[] args)
        {
            var dt1 = new DataTable();
            dt1.Columns.AddRange(new[]
            {
                new DataColumn("Id", typeof(int)),
                new DataColumn("Name", typeof(string)),
                new DataColumn("Age",typeof(string))
            });

            var dt2 = new DataTable();
            dt2.Columns.AddRange(new[]
            {
                new DataColumn("Id", typeof(int)),
                new DataColumn("Name",typeof(string)),
                new DataColumn("Age",typeof(string))
            });

            dt1.Rows.Add(new object[] { 1, "Peter", "20" });
            dt1.Rows.Add(new object[] { 2, "John", "30" });

            dt2.Rows.Add(new object[] { 1, "Peter", "20" });
            dt2.Rows.Add(new object[] { 2, "John", "30" });
            dt2.Rows.Add(new object[] { 3, "Robert", "30" });

            var except = dt2.AsEnumerable().Except(dt1.AsEnumerable(), new RowsComparer());

            foreach (DataRow row in except)
                Console.WriteLine($"Id = {row[0]}, Name = {row[1]}, Age = {row[2]}");
        }

        class RowsComparer : IEqualityComparer<DataRow>
        {
            public bool Equals(DataRow x, DataRow y)
            {
                int id1 = (int)x["Id"];
                int id2 = (int)y["Id"];
                return id1 == id2;
            }

            public int GetHashCode(DataRow obj)
            {
                int hash = obj[0].GetHashCode() + obj[1].GetHashCode() + obj[2].GetHashCode();
                return hash;
            }
        }
    }

}