SqlCommand Classe

Definizione

public ref class SqlCommand sealed : System::Data::Common::DbCommand, ICloneable

public sealed class SqlCommand : System.Data.Common.DbCommand, ICloneable

type SqlCommand = class
    inherit DbCommand
    interface ICloneable

Public NotInheritable Class SqlCommand
Inherits DbCommand
Implements ICloneable

Ereditarietà

DbCommand

SqlCommand

Implementazioni

ICloneable

Esempio

Nell'esempio seguente viene creato un oggetto SqlConnection, un SqlCommandoggetto e un oggetto SqlDataReader. L'esempio legge i dati, scrivendoli nella console. Infine, l'esempio chiude SqlDataReader e quindi quando SqlConnection esce dai blocchi di Using codice.

using System;
using System.Data;
using Microsoft.Data.SqlClient;


namespace SqlCommandCS
{
    class Program
    {
        static void Main()
        {
            string str = "Data Source=(local);Initial Catalog=Northwind;"
                + "Integrated Security=SSPI";
            ReadOrderData(str);

        }

        private static void ReadOrderData(string connectionString)
        {
            string queryString =
                "SELECT OrderID, CustomerID FROM dbo.Orders;";
            using (SqlConnection connection = new SqlConnection(
                       connectionString))
            {
                SqlCommand command = new SqlCommand(
                    queryString, connection);
                connection.Open();
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        Console.WriteLine(String.Format("{0}, {1}",
                            reader[0], reader[1]));
                    }
                }
            }
        }

Nell'esempio seguente viene illustrato come creare ed eseguire tipi diversi di oggetti SqlCommand.

Prima di tutto è necessario creare il database di esempio eseguendo lo script seguente:

USE [master]
GO

CREATE DATABASE [MySchool]
GO

USE [MySchool]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE procedure [dbo].[CourseExtInfo] @CourseId int
as
select c.CourseID,c.Title,c.Credits,d.Name as DepartmentName
from Course as c left outer join Department as d on c.DepartmentID=d.DepartmentID
where c.CourseID=@CourseId

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
create procedure [dbo].[DepartmentInfo] @DepartmentId int,@CourseCount int output
as
select @CourseCount=Count(c.CourseID)
from course as c
where c.DepartmentID=@DepartmentId

select d.DepartmentID,d.Name,d.Budget,d.StartDate,d.Administrator
from Department as d
where d.DepartmentID=@DepartmentId

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
Create PROCEDURE [dbo].[GetDepartmentsOfSpecifiedYear]
@Year int,@BudgetSum money output
AS
BEGIN
SELECT @BudgetSum=SUM([Budget])
FROM [MySchool].[dbo].[Department]
Where YEAR([StartDate])=@Year

SELECT [DepartmentID]
,[Name]
,[Budget]
,[StartDate]
,[Administrator]
FROM [MySchool].[dbo].[Department]
Where YEAR([StartDate])=@Year

END
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Course]([CourseID] [nvarchar](10) NOT NULL,
[Year] [smallint] NOT NULL,
[Title] [nvarchar](100) NOT NULL,
[Credits] [int] NOT NULL,
[DepartmentID] [int] NOT NULL,
CONSTRAINT [PK_Course] PRIMARY KEY CLUSTERED
(
[CourseID] ASC,
[Year] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Department]([DepartmentID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NOT NULL,
[Budget] [money] NOT NULL,
[StartDate] [datetime] NOT NULL,
[Administrator] [int] NULL,
CONSTRAINT [PK_Department] PRIMARY KEY CLUSTERED
(
[DepartmentID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Person]([PersonID] [int] IDENTITY(1,1) NOT NULL,
[LastName] [nvarchar](50) NOT NULL,
[FirstName] [nvarchar](50) NOT NULL,
[HireDate] [datetime] NULL,
[EnrollmentDate] [datetime] NULL,
CONSTRAINT [PK_School.Student] PRIMARY KEY CLUSTERED
(
[PersonID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[StudentGrade]([EnrollmentID] [int] IDENTITY(1,1) NOT NULL,
[CourseID] [nvarchar](10) NOT NULL,
[StudentID] [int] NOT NULL,
[Grade] [decimal](3, 2) NOT NULL,
CONSTRAINT [PK_StudentGrade] PRIMARY KEY CLUSTERED
(
[EnrollmentID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]

GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
create view [dbo].[EnglishCourse]
as
select c.CourseID,c.Title,c.Credits,c.DepartmentID
from Course as c join Department as d on c.DepartmentID=d.DepartmentID
where d.Name=N'English'

GO
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C1045', 2012, N'Calculus', 4, 7)
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C1061', 2012, N'Physics', 4, 1)
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C2021', 2012, N'Composition', 3, 2)
INSERT [dbo].[Course] ([CourseID], [Year], [Title], [Credits], [DepartmentID]) VALUES (N'C2042', 2012, N'Literature', 4, 2)
SET IDENTITY_INSERT [dbo].[Department] ON

INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (1, N'Engineering', 350000.0000, CAST(0x0000999C00000000 AS DateTime), 2)
INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (2, N'English', 120000.0000, CAST(0x0000999C00000000 AS DateTime), 6)
INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (4, N'Economics', 200000.0000, CAST(0x0000999C00000000 AS DateTime), 4)
INSERT [dbo].[Department] ([DepartmentID], [Name], [Budget], [StartDate], [Administrator]) VALUES (7, N'Mathematics', 250024.0000, CAST(0x0000999C00000000 AS DateTime), 3)
SET IDENTITY_INSERT [dbo].[Department] OFF
SET IDENTITY_INSERT [dbo].[Person] ON

INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (1, N'Hu', N'Nan', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (2, N'Norman', N'Laura', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (3, N'Olivotto', N'Nino', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (4, N'Anand', N'Arturo', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (5, N'Jai', N'Damien', NULL, CAST(0x0000A0BF00000000 AS DateTime))
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (6, N'Holt', N'Roger', CAST(0x000097F100000000 AS DateTime), NULL)
INSERT [dbo].[Person] ([PersonID], [LastName], [FirstName], [HireDate], [EnrollmentDate]) VALUES (7, N'Martin', N'Randall', CAST(0x00008B1A00000000 AS DateTime), NULL)
SET IDENTITY_INSERT [dbo].[Person] OFF
SET IDENTITY_INSERT [dbo].[StudentGrade] ON

INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (1, N'C1045', 1, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (2, N'C1045', 2, CAST(3.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (3, N'C1045', 3, CAST(2.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (4, N'C1045', 4, CAST(4.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (5, N'C1045', 5, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (6, N'C1061', 1, CAST(4.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (7, N'C1061', 3, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (8, N'C1061', 4, CAST(2.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (9, N'C1061', 5, CAST(1.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (10, N'C2021', 1, CAST(2.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (11, N'C2021', 2, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (12, N'C2021', 4, CAST(3.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (13, N'C2021', 5, CAST(3.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (14, N'C2042', 1, CAST(2.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (15, N'C2042', 2, CAST(3.50 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (16, N'C2042', 3, CAST(4.00 AS Decimal(3, 2)))
INSERT [dbo].[StudentGrade] ([EnrollmentID], [CourseID], [StudentID], [Grade]) VALUES (17, N'C2042', 5, CAST(3.00 AS Decimal(3, 2)))
SET IDENTITY_INSERT [dbo].[StudentGrade] OFF
ALTER TABLE [dbo].[Course]  WITH CHECK ADD  CONSTRAINT [FK_Course_Department] FOREIGN KEY([DepartmentID])
REFERENCES [dbo].[Department] ([DepartmentID])
GO
ALTER TABLE [dbo].[Course] CHECK CONSTRAINT [FK_Course_Department]
GO
ALTER TABLE [dbo].[StudentGrade]  WITH CHECK ADD  CONSTRAINT [FK_StudentGrade_Student] FOREIGN KEY([StudentID])
REFERENCES [dbo].[Person] ([PersonID])
GO
ALTER TABLE [dbo].[StudentGrade] CHECK CONSTRAINT [FK_StudentGrade_Student]
GO

Compilare ed eseguire quindi quanto segue:

using System;
using System.Data;
using Microsoft.Data.SqlClient;
using System.Threading.Tasks;

class Program
{

    static class SqlHelper
    {
        // Set the connection, command, and then execute the command with non query.
        public static Int32 ExecuteNonQuery(String connectionString, String commandText,
        CommandType commandType, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(commandText, conn))
                {
                    // There're three command types: StoredProcedure, Text, TableDirect. The TableDirect
                    // type is only for OLE DB.
                    cmd.CommandType = commandType;
                    cmd.Parameters.AddRange(parameters);

                    conn.Open();
                    return cmd.ExecuteNonQuery();
                }
            }
        }

        // Set the connection, command, and then execute the command and only return one value.
        public static Object ExecuteScalar(String connectionString, String commandText,
        CommandType commandType, params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand(commandText, conn))
                {
                    cmd.CommandType = commandType;
                    cmd.Parameters.AddRange(parameters);

                    conn.Open();
                    return cmd.ExecuteScalar();
                }
            }
        }

        // Set the connection, command, and then execute the command with query and return the reader.
        public static SqlDataReader ExecuteReader(String connectionString, String commandText,
        CommandType commandType, params SqlParameter[] parameters)
        {
            SqlConnection conn = new SqlConnection(connectionString);

            using (SqlCommand cmd = new SqlCommand(commandText, conn))
            {
                cmd.CommandType = commandType;
                cmd.Parameters.AddRange(parameters);

                conn.Open();
                // When using CommandBehavior.CloseConnection, the connection will be closed when the
                // IDataReader is closed.
                SqlDataReader reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);

                return reader;
            }
        }
    }

    static void Main(string[] args)
    {
        String connectionString = "Data Source=(local);Initial Catalog=MySchool;Integrated Security=True;";

        CountCourses(connectionString, 2012);
        Console.WriteLine();

        Console.WriteLine("Following result is the departments that started from 2007:");
        GetDepartments(connectionString, 2007);
        Console.WriteLine();

        Console.WriteLine("Add the credits when the credits of course is lower than 4.");
        AddCredits(connectionString, 4);
        Console.WriteLine();

        Console.WriteLine("Please press any key to exit...");
        Console.ReadKey();
    }

    static void CountCourses(String connectionString, Int32 year)
    {
        String commandText = "Select Count([CourseID]) FROM [MySchool].[dbo].[Course] Where Year=@Year";
        SqlParameter parameterYear = new SqlParameter("@Year", SqlDbType.Int);
        parameterYear.Value = year;

        Object oValue = SqlHelper.ExecuteScalar(connectionString, commandText, CommandType.Text, parameterYear);
        Int32 count;
        if (Int32.TryParse(oValue.ToString(), out count))
            Console.WriteLine("There {0} {1} course{2} in {3}.", count > 1 ? "are" : "is", count, count > 1 ? "s" : null, year);
    }

    // Display the Departments that start from the specified year.
    static void GetDepartments(String connectionString, Int32 year)
    {
        String commandText = "dbo.GetDepartmentsOfSpecifiedYear";

        // Specify the year of StartDate
        SqlParameter parameterYear = new SqlParameter("@Year", SqlDbType.Int);
        parameterYear.Value = year;

        // When the direction of parameter is set as Output, you can get the value after
        // executing the command.
        SqlParameter parameterBudget = new SqlParameter("@BudgetSum", SqlDbType.Money);
        parameterBudget.Direction = ParameterDirection.Output;

        using (SqlDataReader reader = SqlHelper.ExecuteReader(connectionString, commandText,
        CommandType.StoredProcedure, parameterYear, parameterBudget))
        {
            Console.WriteLine("{0,-20}{1,-20}{2,-20}{3,-20}", "Name", "Budget", "StartDate",
            "Administrator");
            while (reader.Read())
            {
                Console.WriteLine("{0,-20}{1,-20:C}{2,-20:d}{3,-20}", reader["Name"],
                reader["Budget"], reader["StartDate"], reader["Administrator"]);
            }
        }
        Console.WriteLine("{0,-20}{1,-20:C}", "Sum:", parameterBudget.Value);
    }

    // If credits of course is lower than the certain value, the method will add the credits.
    static void AddCredits(String connectionString, Int32 creditsLow)
    {
        String commandText = "Update [MySchool].[dbo].[Course] Set Credits=Credits+1 Where Credits<@Credits";

        SqlParameter parameterCredits = new SqlParameter("@Credits", creditsLow);

        Int32 rows = SqlHelper.ExecuteNonQuery(connectionString, commandText, CommandType.Text, parameterCredits);

        Console.WriteLine("{0} row{1} {2} updated.", rows, rows > 1 ? "s" : null, rows > 1 ? "are" : "is");
    }
}

Commenti

Quando viene creata un'istanza di , le proprietà di SqlCommand lettura/scrittura vengono impostate sui valori iniziali. Per un elenco di questi valori, vedere il SqlCommand costruttore.

SqlCommand include i metodi seguenti per l'esecuzione di comandi in un database di SQL Server:

È possibile reimpostare la CommandText proprietà e riutilizzare l'oggetto SqlCommand . Tuttavia, è necessario chiudere prima SqlDataReader di poter eseguire un comando nuovo o precedente.

Se un SqlException oggetto viene generato dal metodo che esegue un SqlCommandoggetto , rimane SqlConnection aperto quando il livello di gravità è 19 o minore. Quando il livello di gravità è 20 o superiore, il server in genere chiude .SqlConnection Tuttavia, l'utente può riaprire la connessione e continuare.