Executing SQL Server Stored Procedures phần 1

Executing SQL Server Stored Procedures In Chapter 4, you saw how to create and execute SQL Server stored procedures using T-SQL.. This is because you can read values that are returned fr

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Executing SQL Server Stored Procedures

In Chapter 4, you saw how to create and execute SQL Server stored procedures using T-SQL You execute a stored procedure using the T-SQL EXECUTE statement In this section, you'll see how to execute SQL Server procedures using ADO.NET

In Table 8.1, shown earlier in this chapter, I mentioned the CommandType of

StoredProcedure Although you can use this CommandType to indicate that a command

is to execute a stored procedure, you're actually better off using the T-SQL EXECUTE command to execute a stored procedure This is because you can read values that are returned from a stored procedure through a RETURN statement, which you can't do when setting the CommandType to StoredProcedure Also, it's a lot easier to understand your code when you use the EXECUTE command

There are a couple of ways you can execute a stored procedure depending on whether

your procedure returns a result set (a result set is one or more rows retrieved from a table

by a SELECT statement) You'll learn these two ways to execute a stored procedure next

Executing a Stored Procedure That Does Not Return a Result Set

If your procedure does not 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 for the procedure call to your Command object, remembering to set the Direction property for any output parameters to

ParameterDirection.Output These output parameters can be defined using the T-SQL OUTPUT keyword in your procedure call, or returned using a RETURN statement in your actual procedure

3 Execute your Command object using the ExecuteNonQuery() method You use this method because the procedure doesn't return a result set

4 Read the values of any output parameters

You'll see how to use these four steps to call the following two SQL Server stored

procedures:

• The first procedure, AddProduct(), will return an output parameter defined using

the OUTPUT keyword

• The second procedure, AddProduct2(), will return an output parameter using the

RETURN statement

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These examples will show you the possible ways to execute a stored procedure using ADO.NET and read the output parameters

Executing the AddProduct() Stored Procedure

In Chapter 4, you saw how to create a stored procedure in the SQL Server Northwind database The procedure you saw was named AddProduct(), and Listing 8.11 shows the AddProduct.sql script that creates the AddProduct() procedure You saw how to run this script in Chapter 4 If you didn't already run this script when reading Chapter 4, and you want to run the example C# program shown later, you'll need to run this script

AddProduct() adds a row to the Products table and returns the ProductID of the new row

as an OUTPUT parameter

Listing 8.11: ADDPRODUCT.SQL

/*

AddProduct.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

in an OUTPUT parameter named @MyProductID

*/

CREATE PROCEDURE AddProduct

@MyProductID int OUTPUT,

@MyProductName nvarchar(40),

@MySupplierID int,

@MyCategoryID int,

@MyQuantityPerUnit nvarchar(20),

@MyUnitPrice money,

@MyUnitsInStock smallint,

@MyUnitsOnOrder smallint,

@MyReorderLevel smallint,

@MyDiscontinued bit

AS

- 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

)

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- 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

SELECT @MyProductID = SCOPE_IDENTITY()

Notice the OUTPUT parameter named @MyProductID returned by AddProduct()

Because AddProduct() doesn't return a result set, you use the first set of steps outlined earlier Let's examine the details of these four steps to execute this stored procedure

Step 1: Create a Command Object and set its CommandText Property to an

EXECUTE Statement

Your first step is to create a Command object and set its CommandText property to an EXECUTE statement containing the call to AddProduct(); notice the parameter

placeholders used to mark the position where the parameter values will be substituted in step 2:

SqlCommand mySqlCommand = mySqlConnection.CreateCommand();

mySqlCommand.CommandText =

"EXECUTE AddProduct @MyProductID OUTPUT, @MyProductName, " +

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

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

"@MyReorderLevel, @MyDiscontinued";

Notice the OUTPUT parameter placeholder named @MyProductID This is used to store the OUTPUT parameter returned by AddProduct() The other parameter placeholders are used to pass values to AddProduct(), which then uses those values in its INSERT

statement

Step 2: Add Any Required Parameters to the Command Object

Your second step is to add any parameters to your Command object, remembering to set the Direction property for any output parameters to ParameterDirection.Output

In this example, AddProduct() expects an output parameter to store the ProductID for the new row, and you therefore need to add an output parameter to your Command object You do this by setting the Direction property of your parameter to

ParameterDirection.Output For example:

mySqlCommand.Parameters.Add("@MyProductID", SqlDbType.Int);

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mySqlCommand.Parameters["@MyProductID"].Direction =

ParameterDirection.Output;

The other parameters required to call AddProduct() are:

mySqlCommand.Parameters.Add(

"@MyProductName", SqlDbType.NVarChar, 40).Value = "Widget";

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

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

"@MyQuantityPerUnit", SqlDbType.NVarChar, 20).Value = "1 per box";

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

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

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

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

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

Notice that the SqlDbType parameter types correspond to the types expected by the AddProduct() stored procedure The values the parameters are set to are then substituted for the placeholders in the EXECUTE statement shown in step 1

Step 3: Execute the Command Object Using the ExecuteNonQuery() Method

Your third step is to execute your Command object using the ExecuteNonQuery()

method You use ExecuteNonQuery() because the AddProduct() procedure doesn't return

a result set For example:

mySqlCommand.ExecuteNonQuery();

Step 4: Read the Values of any Output Parameters

Your last step is to read the values of any output parameters AddProduct() used one output parameter named @MyProductID You read this returned value from the Value property of @MyProductID:

Console.WriteLine("New ProductID = " +

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

This displays the values of the ProductID generated by SQL Server for the new row in the Products table

Listing 8.12 illustrates these steps to call the AddProduct() procedure

Listing 8.12: EXECUTEADDPRODUCT.CS

/*

ExecuteAddProduct.cs illustrates how to call the SQL Server

AddProduct() stored procedure

*/

using System;

using System.Data;

using System.Data.SqlClient;

class ExecuteAddProduct

{

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 AddProduct @MyProductID OUTPUT, @MyProductName, " + "@MySupplierID, @MyCategoryID, @MyQuantityPerUnit, " +

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

"@MyReorderLevel, @MyDiscontinued";

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