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Updating a Database Table II Create and Delete

Updating a Database Table II Create and Delete. Textbook Chapter 14. 1. Objectives. You will be able to Write C# code to create a new row in a database table from user input. Write C# code of delete a row from a database table. 2. Getting Started. Continue with website from previous hour.

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Updating a Database Table II Create and Delete

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  1. Updating a Database Table IICreate and Delete Textbook Chapter 14 1

  2. Objectives You will be able to • Write C# code to create a new row in a database table from user input. • Write C# code of delete a row from a database table. 2

  3. Getting Started • Continue with website from previous hour. • Add code to • Add a new address to the database. • Delete an address from the database.

  4. Adding an Address to the Database • Let's use a separate page to add an address to the database. • New LinkButton on Default.aspx brings up the new page.

  5. New Address Button Note that CausesValidation is false.

  6. Add New Page • Website > Add New Item • Web Form Add_Address.aspx

  7. Add_Address.aspx Copy table from Default.aspx

  8. Add_Address.aspx Delete ontextchanged and AutoPostBack. Add TabIndex. Add RequiredFieldValidator.

  9. Add_Address.aspx Add Buttons and Label below table

  10. Add_Address.aspx

  11. Click Event Handlers for the Buttons Start with stubs. Try it!

  12. Add to Database Clicked

  13. Real Add to Database • Replace the stub with real code to add a new address to the database. • Instantiate an Address object with user inputs. • Add contents of that object to the database. • We need new "Add New Row" method in class Query. • Takes Address object as parameter.

  14. Add to Database • The function to fill in fields of an Address object from the form is the inverse of the Display_Results method in Default.aspx. • Just reverse the left hand side and right hand side of each assignment statement. • After adding an address to the database clear the TextBoxes

  15. Add_Address.aspx.cs protected void btnAdd_Click(object sender, EventArgs e) { string error_msg = ""; Address adr = new Address(0); adr.Last_name = tbLastName.Text; adr.First_name = tbFirstName.Text; adr.Address1 = tbAddress1.Text; adr.Address2 = tbAddress2.Text; adr.City = tbCity.Text; adr.State = tbState.Text; adr.Zip_code = tbZipCode.Text; Query.Add_to_Database(adr, out error_msg); if (error_msg.Length == 0) lblMessage.Text = "Address added to database"; else lblMessage.Text = error_msg; Clear_Inputs(); } We have to write Query.Add_to_Database().

  16. Clear_Inputs() protected void Clear_Inputs() { tbLastName.Text = ""; tbFirstName.Text = ""; tbAddress1.Text = ""; tbAddress2.Text = ""; tbCity.Text = ""; tbState.Text = ""; tbZipCode.Text = ""; }

  17. Adding a Row to a Database Table • Use the SQL command INSERT. INSERT INTO Table_Name VALUES (val1, val2, ... valn) • For this form of the INSERT command we must provide values for all columns except any Identity column and the values must be in the right order. • We will use command parameters for the values.

  18. Query.Add_to_Database public static void Add_to_Database( Address adr, out string error_msg) { SqlConnection cn = null; string error_msg2 = ""; int nr_rows_affected = 0; try { cn = Setup_Connection(); nr_rows_affected = Perform_Insert(cn, adr); } catch (Exception ex) { error_msg = "ERROR: " + ex.Message; } ...

  19. Query.Add_to_Database (continued) ... finally { if (cn != null) { cn.Close(); } } if (nr_rows_affected != 1) { error_msg2 += " ERROR: Number of rows affected was "; error_msg2 += nr_rows_affected.ToString(); } error_msg = error_msg2; }

  20. Function Perform_Insert private static int Perform_Insert(SqlConnection cn, Address adr) { string cmd_str = "INSERT INTO Addresses " + "VALUES (@Last_name, " + "@First_name, " + "@Address1, " + "@Address2, " + "@City, " + "@State, " + "@Zip_code )"; SqlCommand cmd = new SqlCommand(); cmd.Connection = cn; cmd.CommandText = cmd_str; ...

  21. Function Perform_Insert (continued) ... cmd.Parameters.AddWithValue("@Last_name", adr.Last_name); cmd.Parameters.AddWithValue("@First_name", adr.First_name); cmd.Parameters.AddWithValue("@Address1", adr.Address1); cmd.Parameters.AddWithValue("@Address2", adr.Address2); cmd.Parameters.AddWithValue("@City", adr.City); cmd.Parameters.AddWithValue("@State", adr.State); cmd.Parameters.AddWithValue("@Zip_code", adr.Zip_code); int nr_rows_affected = cmd.ExecuteNonQuery(); return nr_rows_affected; } Try it!

  22. Initial Page Click here

  23. The "Add Address" Page Fill in values.

  24. Values Filled In Click here.

  25. After "Add" Button Clicked

  26. Check the Database End of Section

  27. Deleting an Address • Add a Delete button to the original page. • Disabled until a successful lookup is done. • Deletes the current address when clicked. • Note: • A real app would provide an "Are you sure?" box. • Typically would not really delete the row from the database table. • Instead, set a "Deleted" flag, so that the row could be undeleted. • Avoid irreversible actions!

  28. The Delete Button Double click the Delete button to add an event handler.

  29. Start with a Stub

  30. Delete Button Enabled • Enable the Delete button when a successful lookup is done. • Disable it when the input TextBox is changed.

  31. Lookup Done (Default.aspx.cs) protected void btnLookup_Click(object sender, EventArgs e) { string error_msg; Address adr = Query.Get_Address(tbInput.Text, out error_msg); if (adr == null) { Clear_Results(); Disable_Results_TextBoxes(); ViewState["ID"] = null; } else { Display_Results(adr); Enable_Results_TextBoxes(); btnDelete.Enabled = true; ViewState["ID"] = adr.Id; } lblMessage.Text = error_msg; btnUpdate.Enabled = false; }

  32. Input TextBox Changed protected void tbInput_TextChanged(object sender, EventArgs e) { Clear_Results(); btnUpdate.Enabled = false; Disable_Results_TextBoxes(); btnDelete.Enabled = false; } Default.aspx.cs Try it!

  33. Successful Lookup

  34. Delete Button Clicked

  35. Real Delete Method Default.aspx.cs protected void btnDelete_Click(object sender, EventArgs e) { string error_msg = ""; int id = (int)ViewState["ID"]; Query.Delete_Address(id, out error_msg); if (error_msg.Length > 0) { lblMessage.Text = error_msg; } else { Clear_Results(); lblMessage.Text = "Address Deleted"; } btnDelete.Enabled = false; btnUpdate.Enabled = false; }

  36. Almost identical to Add_to_Database Query.Delete_Address

  37. Query.Perform_Delete public static int Perform_Delete(SqlConnection cn, int id) { string cmd_str = "DELETE FROM Addresses " + " WHERE ID=@ID"; SqlCommand cmd = new SqlCommand(); cmd.Connection = cn; cmd.CommandText = cmd_str; cmd.Parameters.AddWithValue("@ID", id); int nr_rows_affected = cmd.ExecuteNonQuery(); return nr_rows_affected; }

  38. Lookup Address to Delete

  39. Address Deleted

  40. Lookup Again

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