如何将数据插入关系数据库

Question

I have 3 Microsoft SQL Server tables which consist of the following:

• Customer Table

• Training Table

All 3 tables are related.

I need to insert data into the Training table which I can do.

The problem is inserting the CustomerID column of the customers table into the training table by only knowing the customer name.

I created a separate class as I will be using this quite a lot in my applications.

 public void UpdateDatabase(string sql_query)
 {
        using (SqlConnection conn = new SqlConnection(connection_string))
        {
            using (SqlCommand comm = new SqlCommand(sql_query, conn))
            {
                conn.Open();
                comm.ExecuteNonQuery();
                conn.Close();
            }
        }
    }

This is my main class which is used to update my DB.

In my button click even i have the following code.

 private void btnSave_Click(object sender, EventArgs e)
 {
        DB NewJob = new DB();

        if (TabControl1.SelectedTab == TabControl1.TabPages["TPTraining"])//If TPTraiing Tab is selected
            {
                try
                {
                    string Customer = TPTcboCustomer.Text;
                    string Product = TPTcboProduct.Text;
                    DateTime DemoDate = TPTdtpDate.Value.Date;
                    string EndResult = TPTtxtEndResult.Text;

                    NewJob.UpdateDatabase("INSERT INTO TrainingDemos(CustomerID, ProductID, DemoDate, EndResult)VALUES('" + Customer + "','" + Product + "','" + DemoDate + "','" + EndResult + "')");
                    MessageBox.Show("Training/Demo Saved Sussesfully");
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }

The Customer variable holds the customer name that i get from the Customer Table. Instead of inserting the Customer Name into the Training Table i must insert the CustomerID.

string Customer = TPTcboCustomer.Text;

When the form is loaded the TPTcboCustomer combobox control retrieves all customer names from the customer table.

Long story short, how do I insert the CustomerID into the training table by only knowing the customer name.

Answer 1

You'll need to do another query to obtain the CustomerID. Once you have that, you can do your insert.

I mean, you need to verify that it's a real customer anyway, right?

I usually prefer to fill a drop down (or similar field) with customers to choose from anyway when there's a finite number of items to choose from. Personally, I'd do an initial query pulling in all of the customers and populate the drop down with those customer objects. Then you just use the selected item's object information to do your insert.

Make Customer a strong type:

public class Customer
{
    public int Id { get; set; }
    public string Name { get; set; }
    // Other properties as desired

    public override string ToString()
    {
        return Name ?? "<No Name>";
    }
}

Once you have that, read in all of your customers and populate the combo box with your list of Customer objects. The ToString() will make it display the customer's name in the drop down. Then you just have to do:

Customer customer = (Customer)TPTcboCustomer.SelectedItem;

Then BLAM-O, you have all of the customer information you need to do your insert.