Home >Asp.net > Web controls and C# Sharp (Part II)

Web form

As the user is required to insert a new book, the page has to provide a form and some input field.
We are going to use an Asp.Net Web Control that basically provides:

• Making sure the user inputs the mandatory data
• Checking the conformity of the data (for example, integer type of data for the field price)
• Activating the C# code necessary to save the data in the Access database

A web form is an Asp.Net technology to develop rapidly user interfaces. When the page is requested the .Net Framework engine produces an html and JavaScript code, tags and commands such as: text and button input or Onclick events, etc.
Indeed, web form and web controls are objects of .Net Framework installed on the web server, usually Microsoft IIS and then they are Runat=server.
Let's see the whole code for the web control:



As you can see, some html is incapsulated in the web form.
Let's focus on some of the main properties of these web controls.
The TextBox control prints on video a textbox input field and identified the inputed value by an id.

<asp:TextBox id="title" Runat= "server"/>

The RequiredFieldValidator control provides validation of mandatory field, the property ControlToValidate identified by id the mandatory field.
The property ErrorMessage prints the message when the filed is left empty.

<asp:RequiredFieldValidator id="rfvname" ControlToValidate="title"
ErrorMessage="*Mandatory"
Font-Bold= "True" Runat="server" />

As you see the default font color is red:



The CompareValidator control provides logical validation of input data.
When the property EnableClientScript is set true, the Asp.net engine generates client code (JavaScript) so the validation is executed without send to the server another request. In our example, we think that for our hypothetical user appreciates time saving controls, we test positively the page with some browser non Microsoft (as Firefox), and then we decide to keep true this property...
The property Type declares the type of data allowed, in fact for the field price is Integer.
The property Operator if is set to DataTypeCheck to check the type of input data is conformant with the type declared.


<asp: CompareValidator id="Compare2"
ControlToValidate="price"
EnableClientScript="True"
Type="Currency"
Operator="DataTypeCheck"
ErrorMessage="Incorrect type"
Font-Bold= "True"
runat="server"/>


No doubt, the property ErrorMessage prints the message when the filed is left empty:



The Button control is the last element in our form. It prints the button that, if pressed, (event OnCLick) submits the form and launches the C# btnAddBook_Click() function.

<asp:Button id="LinksPost" Text="Save data" OnClick="btnAddBook_Click" Runat="server" />


The output of this web form looks something like this:

Setting the Sql statement after the button click event

The function btnAddBook_Click()'duty is retrieve data from the web form, composing the insert sql statement and pass this string to the function ExecuteSqlCommand() that actually inserts the new row in the table.
As mentioned above, the function btnAddBook_Click() is activated by the button at the end of the web form.

private void btnAddBook_Click(object sender, System.EventArgs e)
{

// Declaring variables
string vtitle, vauthor,vyear,vdate,vprice;
// Reading, encoding and setting variables
vtitle = Server.HtmlEncode(title.Text);
vauthor = Server.HtmlEncode(author.Text);
vyear = Server.HtmlEncode(year.Text);
vprice = price.Text;

// Composing sql insert statement, Now() is going to record the insert time in the data_ins column
string sql = "INSERT INTO books (title,author,pyear,price,date_ins) "
+ " VALUES ('"+ vtitle+ "','"+ vauthor+"','"+ vyear +"',"+ vprice +",Now())";
// Now the sql string is passed to the ExecuteSqlCommand() function designed to execute not Query sql statement
ExecuteSqlCommand(sql);

// At last, for now, we simply reload the page
Response.Redirect("list_insert_books.aspx");

}

Executing a non query statement

A frequent solution to execute insert,delete,update command is developing a function good for any of this type sql statement.
So it is time for ExecuteSqlCommand()function 's code:

// ExecuteNonQuery for insert, delete, update sql command
private void ExecuteSqlCommand(string sql)
{

OleDbConnection conn = null;

try
{
// Connection: defining,creating,opening...
conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; " +
"Data Source=" + Server.MapPath("mydatabase.mdb"));
conn.Open();
//Creating an OleDbCommand command
OleDbCommand cmd =    new OleDbCommand(sql, conn);
//Finally executing the sql command
cmd.ExecuteNonQuery();
}
//the catch construct in case connection, query or else goes wrong prints the relative error message
catch (Exception e)
{
Response.Write(e.Message);
Response.End();
}
// always call Close when done reading.
finally
{
if (conn != null) conn.Close();
}

}

Now, it up to you developing further this script ... enjoying your programming!

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Downloads:
bookstore.zip ( 12 KB)

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1-Web controls and C# Sharp (Part I) | 2-Web controls and C# Sharp (Part II) |

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Marco Magnani marcomagnani@fishscript.com

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