Question

I fill the data set twice,

the table name never set correctly.
I see only one table in the DataSet

What is chances?

public static DataSet GetSchoolTree()
        {
            BLLBase.CreateConnection();
            BLLBase.Connection.Open();

            DataSet dataSet = new DataSet("SS");


            Stages.GetStages(ref dataSet);
            Schools.GetSchools(ref dataSet);

            BLLBase.Connection.Close();

            dataSet.Relations.Add(dataSet.Tables["Schools"].Columns["ID"], dataSet.Tables["dbo.Stages"].Columns["School_ID"]);

            return dataSet;
        }

 internal static void GetSchools(ref DataSet dataSet)
        {
            SqlDataAdapter adapter = new SqlDataAdapter();
            adapter.TableMappings.Add("dbo.Schools", "Schools");

            SqlCommand command = new SqlCommand();
            command.CommandText = "[dbo].[SR_School_ALL]";
            command.CommandType = System.Data.CommandType.StoredProcedure;
            command.Connection = BLLBase.Connection;
            adapter.SelectCommand = command;

            adapter.Fill(dataSet);
        }

 internal static void GetStages(ref DataSet dataSet)
        {
            SqlDataAdapter adapter = new SqlDataAdapter();
            adapter.TableMappings.Add("dbo.Stages", "Stages");

            SqlCommand command = new SqlCommand();
            command.CommandText = "[dbo].[Stp_Stages_All]";
            command.CommandType = System.Data.CommandType.StoredProcedure;
            command.Connection = BLLBase.Connection;
            adapter.SelectCommand = command;

            adapter.Fill(dataSet);
        }

thanks

Answer 1

Calling .Fill() on a dataset will re-load it, not load new results into a different table. Instead, call .Fill() on a table within the dataset. You might want to try something like this:

var ds = new DataSet();
ds.Tables.Add(new DataTable("first"));
adapter1.Fill(ds.Tables["first"]);
ds.Tables.Add(new DataTable("second"));
adapter2.Fill(ds.Tables["second"]);