11

Updating a Database Table IICreate and Delete

Textbook Chapter 14

22

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.

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

Try it!

Start with stubs.

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

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().

Add_Address.aspx.cs

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.

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

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;

}

Default.aspx.cs

36

Query.Delete_Address

Almost identical to Add_to_Database

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