需要有关从SQL Server CE数据库中删除行的帮助

Question

Another question today. This time, I'm having trouble deleting a row from a SQL Server CE database.

private void Form1_Load(object sender, EventArgs e)
{
        // Create a connection to the file datafile.sdf in the program folder
        string dbfile = new System.IO.FileInfo(System.Reflection.Assembly.GetExecutingAssembly().Location).DirectoryName + "\\userDtbs.sdf";
        SqlCeConnection connection = new SqlCeConnection("datasource=" + dbfile);

        // Read all rows from the table test_table into a dataset (note, the adapter automatically opens the connection)
        SqlCeDataAdapter adapter = new SqlCeDataAdapter("SELECT * FROM history", connection);
        DataSet data = new DataSet();
        adapter.Fill(data);

        //Delete from the database
        using (SqlCeCommand com = new SqlCeCommand("DELETE FROM accounts WHERE Id = 0", connection))
        {
            com.ExecuteNonQuery();
        }

        // Save data back to the databasefile
        var cmd = new SqlCeCommandBuilder(adapter);
        adapter.Update(data);

        // Close 
        connection.Close();
}

My program's giving me an error telling me that connection is in a closed state, and I can't figure out why it would close before the DELETE command is executed.

Answer 1

Note that: executing command with Command.ExecuteXXX() requires the connection to be open first. Filling data into DataSet using SqlDataAdapter.Fill doesn't require that because it handles that internally. Executing the SQL query this way is direct and don't require any Update method call on adapter (as you add in your code after deleting). Update is just for saving changes made on your DataSet .

    //Delete from the database
    using (SqlCeCommand com = new SqlCeCommand("DELETE FROM accounts WHERE Id = 0", connection))
    {
        if(connection.State == ConnectionState.Closed) connection.Open();
        com.ExecuteNonQuery();
    }