Executing SQL Server Stored Procedures phần 2

Executing the AddProduct2 Stored Procedure As you'll see, the AddProduct2 procedure is similar to AddProduct, except that it uses a RETURN statement instead of an OUTPUT parameter to re

The output from this program is as follows:

New ProductID = 81

Of course, depending on the existing rows in your Products table, you'll get a different result

Executing the AddProduct2() Stored Procedure

As you'll see, the AddProduct2() procedure is similar to AddProduct(), except that it uses

a RETURN statement instead of an OUTPUT parameter to return the ProductID for the new row Listing 8.13 shows the AddProduct2.sql script that creates the AddProduct2() procedure You'll need to run this script before running the C# program

Listing 8.13: ADDPRODUCT2.SQL

/*

AddProduct2.sql creates a procedure that adds a row to the

Products table using values passed as parameters to the

procedure The procedure returns the ProductID of the new row

using a RETURN statement

*/

CREATE PROCEDURE AddProduct2

@MyProductName nvarchar(40),

@MySupplierID int,

@MyCategoryID int,

@MyQuantityPerUnit nvarchar(20),

@MyUnitPrice money,

@MyUnitsInStock smallint,

@MyUnitsOnOrder smallint,

@MyReorderLevel smallint,

@MyDiscontinued bit

AS

- declare the @MyProductID variable

DECLARE @MyProductID int

- insert a row into the Products table

INSERT INTO Products (

ProductName, SupplierID, CategoryID, QuantityPerUnit,

UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel,

Discontinued

) VALUES (

@MyProductName, @MySupplierID, @MyCategoryID, @MyQuantityPerUnit, @MyUnitPrice, @MyUnitsInStock, @MyUnitsOnOrder, @MyReorderLevel,

@MyDiscontinued

)

- use the SCOPE_IDENTITY() function to get the last

- identity value inserted into a table performed within

- the current database session and stored procedure,

- so SCOPE_IDENTITY returns the ProductID for the new row

- in the Products table in this case

SET @MyProductID = SCOPE_IDENTITY()

RETURN @MyProductID

Notice the RETURN statement at the end to return @MyProductID Because

AddProduct2() doesn't return a result set of rows, you use the same four steps shown in the previous section to execute the procedure using ADO.NET The only difference is in the construction of your EXECUTE command when setting the CommandText property

in step 1 To call AddProduct2() you set the CommandText property of your Command object as follows:

mySqlCommand.CommandText =

"EXECUTE @MyProductID = AddProduct2 @MyProductName, " +

"@MySupplierID, @MyCategoryID, @MyQuantityPerUnit, " +

"@MyUnitPrice, @MyUnitsInStock, @MyUnitsOnOrder, " +

"@MyReorderLevel, @MyDiscontinued";

Notice the change in the position of the @MyProductID parameter: it is shifted to just after the EXECUTE and set equal to the value returned by AddProduct2() This change is made because Add-Product2() uses a RETURN statement to output the @MyProductID value The rest of the C# code required to call AddProduct2() is the same as that shown earlier in Listing 8.12

Note Because only the EXECUTE is different, I've omitted the program that calls

AddProduct2() from this book You can see this program in the

ExecuteAddProduct2.cs file I've provided Feel free to examine and run it

Executing a Stored Procedure that Does Return a Result Set

If your procedure does return a result set, then you use the following steps to execute it:

1 Create a Command object and set its CommandText property to an EXECUTE statement containing your procedure call

2 Add any required parameters to your Command object, remembering to set the Direction property for any output parameters to ParameterDirection.Output

3 Execute your command using the ExecuteReader() method, storing the returned DataReader object

4 Read the rows in the result set using your DataReader object

5 Close your DataReader object You must do this before you can read any output

parameters

6 Read the values of any output parameters

In the following example, you'll see a stored procedure named AddProduct3() that will return a result set along with an output parameter using a RETURN statement

The AddProduct3() procedure is similar to AddProduct2(), except that it also returns a result set using a SELECT statement This SELECT contains the ProductName and UnitPrice columns for the new row added to the Products table This result set is returned

in addition to the ProductID of the new row, which is returned using the RETURN

statement Listing 8.14 shows the AddProduct3.sql script that creates the AddProduct3() procedure You'll need to run this script before running the C# program

Listing 8.14: ADDPRODUCT3.SQL

/*

AddProduct3.sql creates a procedure that adds a row to the

Products table using values passed as parameters to the

procedure The procedure returns the ProductID of the new row

using a RETURN statement and returns a result set containing

the new row

*/

CREATE PROCEDURE AddProduct3

@MyProductName nvarchar(40),

@MySupplierID int,

@MyCategoryID int,

@MyQuantityPerUnit nvarchar(20),

@MyUnitPrice money,

@MyUnitsInStock smallint,

@MyUnitsOnOrder smallint,

@MyReorderLevel smallint,

@MyDiscontinued bit

AS

- declare the @MyProductID variable

DECLARE @MyProductID int

- insert a row into the Products table

INSERT INTO Products (

ProductName, SupplierID, CategoryID, QuantityPerUnit,

UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel,

Discontinued

) VALUES (

@MyProductName, @MySupplierID, @MyCategoryID, @MyQuantityPerUnit, @MyUnitPrice, @MyUnitsInStock, @MyUnitsOnOrder, @MyReorderLevel,

@MyDiscontinued

)

- use the SCOPE_IDENTITY() function to get the last

- identity value inserted into a table performed within

- the current database session and stored procedure,

- so SCOPE_IDENTITY returns the ProductID for the new row

- in the Products table in this case

SET @MyProductID = SCOPE_IDENTITY()

- return the result set

SELECT ProductName, UnitPrice

FROM Products

WHERE ProductID = @MyProductID

- return @MyProductID

RETURN @MyProductID

Since you've already seen the basics for the code that execute the six steps shown earlier

in this section, I'll go straight to the code with minimal explanation Listing 8.15 shows the program that calls AddProduct3() The important things to notice are:

Listing 8.15: EXECUTEADDPRODUCT3.CS

/*

ExecuteAddProduct3.cs illustrates how to call the SQL Server

AddProduct3() stored procedure

*/

using System;

using System.Data;

using System.Data.SqlClient;

class ExecuteAddProduct3

{

public static void Main()

{

SqlConnection mySqlConnection =

new SqlConnection(

"server=localhost;database=Northwind;uid=sa;pwd=sa"

);

mySqlConnection.Open();

// step 1: create a Command object and set its CommandText

// property to an EXECUTE statement containing the stored

// procedure call

SqlCommand mySqlCommand = mySqlConnection.CreateCommand(); mySqlCommand.CommandText =

"EXECUTE @MyProductID = AddProduct3 @MyProductName, " + "@MySupplierID, @MyCategoryID, @MyQuantityPerUnit, " +

"@MyUnitPrice, @MyUnitsInStock, @MyUnitsOnOrder, " +

"@MyReorderLevel, @MyDiscontinued";

// step 2: add the required parameters to the Command object

mySqlCommand.Parameters.Add("@MyProductID", SqlDbType.Int); mySqlCommand.Parameters["@MyProductID"].Direction =

ParameterDirection.Output;

mySqlCommand.Parameters.Add(

"@MyProductName", SqlDbType.NVarChar, 40).Value = "Widget"; mySqlCommand.Parameters.Add(

"@MySupplierID", SqlDbType.Int).Value = 1;

mySqlCommand.Parameters.Add(

"@MyCategoryID", SqlDbType.Int).Value = 1;

mySqlCommand.Parameters.Add(

"@MyQuantityPerUnit", SqlDbType.NVarChar, 20).Value = "1 per box"; mySqlCommand.Parameters.Add(

"@MyUnitPrice", SqlDbType.Money).Value = 5.99;

mySqlCommand.Parameters.Add(

"@MyUnitsInStock", SqlDbType.SmallInt).Value = 10;

mySqlCommand.Parameters.Add(

"@MyUnitsOnOrder", SqlDbType.SmallInt).Value = 5;

mySqlCommand.Parameters.Add(

"@MyReorderLevel", SqlDbType.SmallInt).Value = 5;

mySqlCommand.Parameters.Add(

"@MyDiscontinued", SqlDbType.Bit).Value = 1;

// step 3: execute the Command object using the ExecuteReader()

// method

SqlDataReader mySqlDataReader = mySqlCommand.ExecuteReader();

// step 4: read the rows using the DataReader object

while (mySqlDataReader.Read())

{

Console.WriteLine("mySqlDataReader[\" ProductName\"] = " +

mySqlDataReader["ProductName"]);

Console.WriteLine("mySqlDataReader[\" UnitPrice\"] = " +

mySqlDataReader["UnitPrice"]);

}

// step 5: close the DataReader object

mySqlDataReader.Close();

// step 6: read the value of the output parameter

Console.WriteLine("New ProductID = " +

mySqlCommand.Parameters["@MyProductID"].Value);

mySqlConnection.Close();

}

}

The ExecuteReader() method is used to return the result set containing the ProductName and UnitPrice columns for the new row

The result set is then read using a SqlDataReader object

The SqlDataReader object is closed before the output parameter is read

The output from this program is as follows:

mySqlDataReader["ProductName"] = Widget

mySqlDataReader["UnitPrice"] = 5.99

New ProductID = 83