如何基于VS2012上另一个数据网格的选定行在数据网格上显示SQL队列结果

Question

Here is my code:

public void loadGrid1() {
                con.Open();
                cmd = new SqlCommand(@"SELECT StudID, Stud_Lname, Stud_Fname FROM STUDENTS;",con);
                rdr = cmd.ExecuteReader();
                while (rdr.Read()) {
                    dataGridView2.Rows.Add(rdr[0].ToString(), rdr[1].ToString(), rdr[2].ToString());
                }
                con.Close();
}

public void loadGrid3() {
                con.Open();
                cmd = new SqlCommand(@"SELECT Title, Author FROM Books INNER JOIN Borrow ON Borrow.BookID = Books.BookID WHERE Borrow.StudID = '"+dataGridView2.SelectedRows[0].Cells[0].Value.ToString()+"';", con);
                rdr = cmd.ExecuteReader();
                while (rdr.Read()) {
                    dataGridView3.Rows.Add(rdr[0].ToString(), rdr[1].ToString());
                }
                con.Close();
}

loadGrid1 is the function I used to load contents of grid 1 , while loadGrid3 is supposed to show the Books borrowed on grid 3 by the selected student from grid 1 .

What am I doing wrong?

Answer 1

First, your query is susceptible to sql injection. That aside, you might want to check what is the actual query that is getting created here, if at all:

SqlCommand(@"SELECT Title, Author FROM Books INNER JOIN Borrow ON Borrow.BookID = Books.BookID WHERE Borrow.StudID = '"+dataGridView2.SelectedRows[0].Cells[0].Value.ToString()+"';");

perhaps change it to this?:

string qryString = @"SELECT Title, Author FROM Books INNER JOIN Borrow ON Borrow.BookID = Books.BookID WHERE Borrow.StudID = '"+dataGridView2.SelectedRows[0].Cells[0].Value.ToString()+"';"

SqlCommand(qryString);

Edit 1: When is Loadgrid3 method being called?

Edit 2: Try and change the code as follows:

public void loadGrid1()
{
    con.Open();
    cmd = new SqlCommand(@"SELECT StudID, Stud_Lname, Stud_Fname FROM STUDENTS;",con);
    rdr = cmd.ExecuteReader();
    while (rdr.Read())
    {
        dataGridView2.Rows.Add(rdr[0].ToString(), rdr[1].ToString(), rdr[2].ToString());
    }

    // check if dataGridView2 has more than 0 rows
    // and then select the first row by default
    if(dataGridView2.Rows.Count > 0)
    {
        dataGridView2.Rows[0].Selected = true
    }
    con.Close();
}

Remember this is a dirty fix for your immediate question, but you might want to do something with datagridview events etc.