ASP.NET 4 Unleased - p 90 potx

When you execute the SqlCommand, the following command is sent to Microsoft SQL Server: exec sp_executesql N’INSERT Titles Title VALUES @Title’, ➥N’@Title nvarchar17’, @Title = N’ASP.NET

The first statement creates a SqlCommand object that represents a SQL INSERT command

The command includes a parameter named @Title

The second statement adds a SqlParameter to the SqlCommand object’s Parameters

collec-tion The AddWithValue() method enables you to add a parameter with a certain name

and value In this case, the method supplies the value for the @Title parameter

When you execute the SqlCommand, the following command is sent to Microsoft

SQL Server:

exec sp_executesql N’INSERT Titles (Title) VALUES (@Title)’,

➥N’@Title nvarchar(17)’, @Title = N’ASP.NET 4.0 Unleashed’

The SqlCommand object calls the sp_executesql stored procedure when it executes a

command In this case, it passes the type, size, and value of the @Title parameter to the

sp_executesql stored procedure

When you use AddWithValue(), the SqlCommand object infers the type and size of the

para-meter for you The method assumes that string values are SQL NVarChar values, integer

values are SQL Int values, decimal values are SQL decimal values, and so on

As an alternative to using the AddWithValue() method, you can create a SqlParameter

explicitly and add the SqlParameter to a SqlCommand object’s Parameters collection The

advantage of creating a parameter explicitly is that you can specify parameter properties

explicitly, such as its name, type, size, precision, scale, and direction

For example, the following code creates a parameter named @Title with a particular data

type, size, and value:

SqlCommand cmd = new SqlCommand(“INSERT Titles (Title) VALUES (@Title)”, con);

SqlParameter paramTitle = new SqlParameter();

paramTitle.ParameterName = “@Title”;

paramTitle.SqlDbType = SqlDbType.NVarChar;

paramTitle.Size = 50;

paramTitle.Value = “ASP.NET 4.0 Unleashed”;

cmd.Parameters.Add(paramTitle);

If this seems like a lot of code to do something simple, you can use one of the overloads

of the Add() method to create a new SqlParameter like this:

SqlCommand cmd = new SqlCommand(“INSERT Test (Title) VALUES (@Title)”, con);

cmd.Parameters.Add(“@Title”, SqlDbType.NVarChar,50).Value = “ASP.NET 4.0

➥Unleashed”;

In general, in this book and in the code that I write, I use the AddWithValue() method to

create parameters I like the AddWithValue() method because it involves the least typing

Executing a Command That Represents a Stored Procedure

You can use a SqlCommand object to represent a Microsoft SQL Server stored procedure For

example, you can use the following two statements to create a SqlCommand object that

represents a stored procedure named GetTitles:

SqlCommand cmd = new SqlCommand(“GetTitles”, con);

cmd.CommandType = CommandType.StoredProcedure;

When you execute this SqlCommand, the GetTitles stored procedure is executed When

you create SqlParameters for a SqlCommand that represents a stored procedure, the

SqlParameters represent stored procedure parameters The modified Movie component in

Listing 19.9 uses stored procedures to retrieve and update movie records

LISTING 19.9 App_Code\Movie4.cs

using System;

using System.Data;

using System.Data.SqlClient;

using System.Web.Configuration;

using System.Collections.Generic;

public class Movie4

{

private static readonly string _connectionString;

private int _id;

private string _title;

private string _director;

public int Id

{

get { return _id; }

set { _id = value; }

}

public string Title

{

get { return _title; }

set { _title = value; }

}

public string Director

{

get { return _director; }

set { _director = value; }

}

public void Update(int id, string title, string director)

{

SqlConnection con = new SqlConnection(_connectionString);

SqlCommand cmd = new SqlCommand(“MovieUpdate”, con);

cmd.CommandType = CommandType.StoredProcedure;

cmd.Parameters.AddWithValue(“@Id”, id);

cmd.Parameters.AddWithValue(“@Title”, title);

cmd.Parameters.AddWithValue(“@Director”, director);

using (con)

{

con.Open();

cmd.ExecuteNonQuery();

}

}

public List<Movie4> GetAll()

{

List<Movie4> results = new List<Movie4>();

SqlConnection con = new SqlConnection(_connectionString);

SqlCommand cmd = new SqlCommand(“MovieSelect”, con);

cmd.CommandType = CommandType.StoredProcedure;

using (con)

{

con.Open();

SqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())

{

Movie4 newMovie = new Movie4();

newMovie.Id = (int)reader[“Id”];

newMovie.Title = (string)reader[“Title”];

newMovie.Director = (string)reader[“Director”];

results.Add(newMovie);

}

}

return results;

}

static Movie4()

{

_connectionString =

WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString;

}

}

The component in Listing 19.9 uses the MovieSelect and MovieUpdate stored procedures

contained in Listing 19.10

LISTING 19.10 MovieStoredProcedures.sql

CREATE PROCEDURE dbo.MovieSelect

AS

SELECT Id, Title, Director FROM Movies

CREATE PROCEDURE dbo.MovieUpdate

(

@Id int,

@Title NVarchar(100),

@Director NVarchar(100)

)

AS

UPDATE Movies SET

Title = @Title,

Director = @Director

WHERE Id = @Id

The ASP.NET page in Listing 19.11 contains a GridView that is bound to the modified

Movie component This GridView enables you to display and update movie records

LISTING 19.11 ShowMovie4.aspx

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

<html xmlns=”http://www.w3.org/1999/xhtml” >

<head id=”Head1” runat=”server”>

<title>Show Movie4</title>

</head>

<body>

<form id=”form1” runat=”server”>

<div>

<asp:GridView

id=”grdMovies”

DataSourceID=”srcMovies”

DataKeyNames=”Id”

AutoGenerateEditButton=”true”

Runat=”server” />

<asp:ObjectDataSource

id=”srcMovies”

TypeName=”Movie4”

SelectMethod=”GetAll”

UpdateMethod=”Update”

Runat=”server” />

</div>

</form>

</body>

</html>

You can use a SqlParameter to represent not only stored procedure input parameters, but

also to represent stored procedure return values and output parameters If you need to

return an integer value from a stored procedure, you can create a SqlParameter that

repre-sents a return value For example, the stored procedure in Listing 19.12 returns the

number of rows in the Movies database table

LISTING 19.12 GetMovieCount.sql

CREATE PROCEDURE dbo.GetMovieCount

AS

RETURN (SELECT COUNT(*) FROM Movies)

The page in Listing 19.13 displays the return value from the GetMovieCount stored

proce-dure with a Label control (see Figure 19.6)

FIGURE 19.6 Displaying a stored procedure return value

LISTING 19.13 ShowMovieCount.aspx

<%@ Page Language=”C#” %>

<%@ Import Namespace=”System.Data” %>

<%@ Import Namespace=”System.Data.SqlClient” %>

<%@ Import Namespace=”System.Web.Configuration” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

<script runat=”server”>

void Page_Load()

{

lblMovieCount.Text = GetMovieCount().ToString();

}

private int GetMovieCount()

{

int result = 0;

string connectionString =

WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString;

SqlConnection con = new SqlConnection(connectionString);

SqlCommand cmd = new SqlCommand(“GetMovieCount”, con);

cmd.CommandType = CommandType.StoredProcedure;

cmd.Parameters.Add(“@ReturnVal”, SqlDbType.Int).Direction =

➥ParameterDirection.ReturnValue;

using (con)

{

con.Open();

cmd.ExecuteNonQuery();

result = (int)cmd.Parameters[“@ReturnVal”].Value;

}

return result;

}

</script>

<html xmlns=”http://www.w3.org/1999/xhtml” >

<head id=”Head1” runat=”server”>

<title>Show Movie Count</title>

</head>

<body>

<form id=”form1” runat=”server”>

<div>

There are

<asp:Label

id=”lblMovieCount”

Runat=”server” />

movies in the database

</div>

</form>

</body>

</html>

In Listing 19.13, a SqlParameter is created that has the name ReturnVal The name of the

SqlParameter is not important However, the SqlParameter.Direction property is set to

the value ReturnValue After the SqlCommand is executed, the return value can be retrieved

by reading the value of this parameter

A stored procedure has only one return value, and it must be an integer value If you need

to return more than one value, or values of a different data type than an integer, you need

to use stored procedure output parameters

For example, the stored procedure in Listing 19.14 returns movie titles and box office

totals The stored procedure includes an output parameter named @SumBoxOfficeTotals

This output parameter represents a sum of all box office totals

LISTING 19.14 GetBoxOfficeTotals.sql

CREATE PROCEDURE dbo.GetBoxOfficeTotals

(

@SumBoxOfficeTotals Money OUTPUT

)

AS

Assign Sum Box Office Totals

SELECT @SumBoxOfficeTotals = SUM(BoxOfficeTotals) FROM Movies

Return all rows

SELECT Title, BoxOfficeTotals FROM Movies

The data access component in Listing 19.15 contains a method named GetBoxOffice()

that calls the GetBoxOfficeTotals stored procedure The method adds an output

parame-ter to the SqlCommand object

LISTING 19.15 App_Code\Movie5.cs

using System;

using System.Data;

using System.Data.SqlClient;

using System.Web.Configuration;

using System.Collections.Generic;

public class Movie5

{

private static readonly string _connectionString;

private string _title;

private decimal _boxOfficeTotals;

public string Title

{

get { return _title; }

set { _title = value; }

}

public decimal BoxOfficeTotals

{

get { return _boxOfficeTotals; }

set { _boxOfficeTotals = value; }

}

public List<Movie5> GetBoxOffice(out decimal SumBoxOfficeTotals)

{

List<Movie5> results = new List<Movie5>();

SqlConnection con = new SqlConnection(_connectionString);

SqlCommand cmd = new SqlCommand(“GetBoxOfficeTotals”, con);

cmd.CommandType = CommandType.StoredProcedure;

cmd.Parameters.Add(“@SumBoxOfficeTotals”, SqlDbType.Money).Direction =

ParameterDirection.Output;

using (con)

{

con.Open();

SqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())

{

Movie5 newMovie = new Movie5();

newMovie.Title = (string)reader[“Title”];

newMovie.BoxOfficeTotals = (decimal)reader[“BoxOfficeTotals”];

results.Add(newMovie);

}

reader.Close();

SumBoxOfficeTotals =

➥(decimal)cmd.Parameters[“@SumBoxOfficeTotals”].Value;

}

return results;

}

static Movie5()

{

_connectionString =

WebConfigurationManager.ConnectionStrings[“Movies”].ConnectionString;

}

}

In Listing 19.15, the SqlDataReader is explicitly closed before the output parameter is

read If you do not close the SqlDataReader first, attempting to read the value of the

output parameter raises an exception

Finally, the page in Listing 19.16 displays the movie box office totals in a GridView In

addition, it displays the value of the output parameter in a Label control (see Figure 19.7)

FIGURE 19.7 Displaying an output parameter

LISTING 19.16 ShowMovie5.aspx

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN”

“http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd”>

<script runat=”server”>

protected void srcMovies_Selected(object sender,

➥ObjectDataSourceStatusEventArgs e)

{

decimal sum = (decimal)e.OutputParameters[“SumBoxOfficeTotals”];

lblSum.Text = sum.ToString(“c”);

}

</script>

<html xmlns=”http://www.w3.org/1999/xhtml” >

<head id=”Head1” runat=”server”>

<title>Show Movie5</title>

</head>

<body>

<form id=”form1” runat=”server”>

<div>

<asp:GridView

id=”grdMovies”

DataSourceID=”srcMovies”

AutoGenerateColumns=”false”

Runat=”server”>

<Columns>

<asp:BoundField DataField=”Title” HeaderText=”Title” />

<asp:BoundField

DataField=”BoxOfficeTotals”

HeaderText=”Box Office”

HtmlEncode=”false”

DataFormatString=”{0:c}” />

</Columns>

</asp:GridView>

<br />

Sum of Box Office Totals:

<asp:Label

id=”lblSum”

Runat=”server” />

<asp:ObjectDataSource

id=”srcMovies”

TypeName=”Movie5”

SelectMethod=”GetBoxOffice”

Runat=”server” OnSelected=”srcMovies_Selected”>

<SelectParameters>

<asp:Parameter

Name=”SumBoxOfficeTotals”

Type=”Decimal”

Direction=”Output” />

</SelectParameters>

</asp:ObjectDataSource>