How to get a DataAdapter for or from an existing modified strongly-typed DataSet? - ado.net

Question

I have about 10 tables that I load into a DataSet using a single DataAdapter in a sequence. During the load, I use only one DataAdapter, and I replace the table names and SELECT statements as required. I replace the table name and the SQL select statement and successively fill tables in the DataSet. Everything is done inside of two nested "using" statements to dispose of the connection and DataAdapter objects as shown below.
using (OleDbConnection conn = new OleDbConnection (Db.DbConnGet ())) {
using (var da = new OleDbDataAdapter (sql, conn)) {
tablename = "Table1";
da.SelectCommand.CommandText = $"Select * from {tablename}";
try {
da.Fill (hsdset, tablename);
} catch (Exception ex) {
...
}
tablename = "Table2";
da.SelectCommand.CommandText = $"Select * from {tablename}";
try {
da.Fill (hsdset, tablename);
} catch (Exception ex) {
...
}
}}
As you can see, the DataAdapter is disposed of once the loading is done, and I pass the DataSet around my application as necessary for reading data.
But now I have a need to update or extend the data in the dataset and get it back into the database. Updating the DataTables inside the dataset is not a problem - there are many examples on the net. I regenerated a new Connection and DataAdapter to do the update with a table in the existing, modified, strongly-typed DataSet, as follows.
using (OleDbConnection conn = new OleDbConnection (Db.DbConnGet ())) {
using (var da = new OleDbDataAdapter ("", conn)) {
// this is required; I don't know if it is used by Update
da.SelectCommand.CommandText = $"Select * from " + tablename;
try {
// build special update commands from the table->db differences
var cbuilder = new OleDbCommandBuilder (da);
da.Update (dset, "Layers");
} catch (Exception ex) {
...
}
}
}
}
My first question is, "Does the Update operation actually use the original SELECT statement to retrieve info from the database? If not, why is it required? I thought the DataSet kept track of modified rows, new rows, deleted rows, and so on. I thought updating could be done without reading the whole data table again? Or maybe it reads only the records that are marked as modified in the DataTable?
My second question is what is the best (or normal) way of working with DataSets and DataAdapters this way? Is it best practice to always save the original DataAdapters for later use, or is it good practice to create new ones like I did above? (Does the original DataAdapter keep any state information during the load that the newly-created DataAdapter would not have?) Thank you.