How To: Use DataRelation to perform a join on two DataTables in a DataSet?

Question

How do I perform a join between two DataTables in a Dataset?

I created a DataRelation between two tables….then what?

I'm looking at one explanation on how to do it (http://www.emmet-gray.com/Articles/DataTableJoins.htm) which involves copying rows from tables to a result table?

Is there a better way to do this?

Answer 1

See if this helps

DataTable person = new DataTable();
person.Columns.Add("Id");
person.Columns.Add("Name");

DataTable pet = new DataTable();
pet.Columns.Add("Id");
pet.Columns.Add("Name");
pet.Columns.Add("OwnerId");

DataSet ds = new DataSet();
ds.Tables.AddRange(new[] { person, pet });

ds.Relations.Add("PersonPet",person.Columns["Id"], pet.Columns["OwnerId"]);

DataRow p = person.NewRow();
p["Id"] = 1;
p["Name"] = "Peter";
person.Rows.Add(p);

p = person.NewRow();
p["Id"] = 2;
p["Name"] = "Alex";
person.Rows.Add(p);

p = pet.NewRow();
p["Id"] = 1;
p["Name"] = "Dog";
p["OwnerId"] = 1;
pet.Rows.Add(p);

p = pet.NewRow();
p["Id"] = 2;
p["Name"] = "Cat";
p["OwnerId"] = 2;
pet.Rows.Add(p);


foreach (DataRow personRow in person.Rows)
{
    Console.WriteLine("{0} - {1}",personRow["Id"], personRow["Name"]);
    foreach (DataRow petRow in personRow.GetChildRows("PersonPet"))
    {
        Console.WriteLine("{0} - {1}", petRow["Id"], petRow["Name"]);
    }
}

Answer 2

DataTables support selection only on columns they own, joining many tables isn't supported.

Answer 3

I was finding the solution for the same problem. Well, I have given up and use SQL to do a join.

Someone has written some custom code to achieve joining DataTable. Maybe they are helpful for you: http://www.emmet-gray.com/Articles/DataTableJoins.htm