如何使用comboBox从sql数据库绑定dataGridView中的数据？

Question

I am facing unique problem with my code. This is the code for showing tables in comboBox1 its working fine.

ComboBox is filled with school names and when a user select a school in that ComboBox, The students in that school will be shown in DataGridView Please help.

Functionality of this application:

1. Creating a table in sql database(schoolName).
2. Selecting table(select School).
3. Adding values in the school(student information).

error:

1. the datagrid in the bottom is not retrieving properly, its showing something else.

SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=" + Application.StartupPath + "\\Login.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

con.Open();

SqlCommand cmd = new SqlCommand();

cmd.Connection = con;
cmd.CommandType = CommandType.Text;
cmd.CommandText = "SELECT * FROM INFORMATION_SCHEMA.TABLES";

SqlDataAdapter dbAdapter = new SqlDataAdapter(cmd);

DataTable dtRecords = new DataTable();
dbAdapter.Fill(dtRecords);
dataGridView1.DataSource = dtRecords; //dataGrid
comboBox1.DataSource = dtRecords;
comboBox1.DisplayMember = "TABLE_NAME";

con.Close();

Answer 1

First of all check this: http://msdn.microsoft.com/en-us/library/ms186224.aspx

The SQL query SELECT * FROM INFORMATION_SCHEMA.TABLES returns information about the tables that exist in database not the rows of a specefic table

If you want to the information of that table you can rich that by writing a new query in SelectedIndexChanged event of your ComboBox, something like that:

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=" + Application.StartupPath + "\\Login.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

        con.Open();

        SqlCommand cmd = new SqlCommand();

        cmd.Connection = con;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT * FROM " + comboBox1.Text;

        SqlDataAdapter dbAdapter = new SqlDataAdapter(cmd);

        DataTable dtRecords = new DataTable();
        dbAdapter.Fill(dtRecords);
        dataGridView1.DataSource = dtRecords; //dataGrid

        con.Close();
    }

This code can fix this problem, but actually there is a bigger problem and It's about your data structure.

This kind of code tells me there is a table for every school and that's not a normalized database. Lets clear it by an example: Imagine that your manager want to move some students from their school to another school, in this data structure you have to move a record from a table to another table, first you have to find that record that point to our student and then save it in memory and then create a new record in destination table. In this example:

• There is a lot of works to do (There is aa lot of code to write)
• There is a risk that your data will be crupted.
• What happen if this have to be done in 1000 students??!!

In other hand you can simply create table and named it schools that have two main columns: ID , Name and then create a table and named it students that have three main columns: ID , SchoolID , Name every school have a unique id and every student have its own id related to its own school by SchoolID column.