Executing SQL Server Stored Procedures phần 2

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Executing SQL Server Stored Procedures phần 2

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The output from this program is as follows: New ProductID = 81 Of course, depending on the existing rows in your Products table

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Nội dung Text: Executing SQL Server Stored Procedures phần 2

  1. 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,
  2. 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:
  3. 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
  4. 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;
  5. 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;
  6. // 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
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