Question

I am relatively new to C# and am developing an application that communicates with a local database (SQL Compact 3.5). I am fine with running standard select statements – but when it comes to getting that data into C# – I get a bit lost.

What I have so far is a ‘delete’ query that deletes all rows named ‘Master’.
Now I have worked out that I actually need to get the IDs of those rows before I delete them (for database integrity purposes). I have no problems running a standard select query – my problem is getting a selection of rows from SQL CE into a C# application (using arrays or datatables or whatever is most logical/convenient).

This is what I have at the moment, but it only returns one value, not a selection:

string sql = "select listid from list where ShortDesc='Master'";
SqlCeCommand cmdGetOldMasterId = new SqlCeCommand(sql, DbConnection.ceConnection);
int oldKey = (int)cmdGetOldMasterId.ExecuteScalar();
Console.WriteLine("Old ID: " + oldKey);

I need to be able to do perform a foreach{ } loop on each of the returned rows. Any ideas how I can do this in C#?

Answer 1

You need to use a SqlCeDataReader instead of a ExecuteScalar if you suppose that your sql statement returns more thant one row of data

string sql = "select listid from list where ShortDesc='Master'";
SqlCeCommand cmdGetOldMasterId = new SqlCeCommand(sql, DbConnection.ceConnection);
SqlCeDataReader reader = cmdGetOldMasterId.ExecuteReader();
while(reader.Read())
{
    Console.WriteLine(reader[0].ToString());
    // or, if your listid is an integer  
    // int listID = reader.GetInt32(0);   
}

another possibility is to use a SqlCeDataAdapter to fill a DataTable (this is less performant, but more useful if you need to process your data later in a different method)

string sql = "select listid from list where ShortDesc='Master'";
SqlCeCommand cmdGetOldMasterId = new SqlCeCommand(sql, DbConnection.ceConnection);
SqlCeDataAdapter da = new SqlCeDataAdapter(cmdGetOldMasterId);
DataTable dt = new DataTable();
da.Fill(dt);

....
foreach(DataRow r in dt.Rows)
{
    Console.WriteLine(r["listid"].ToString());
}