Export (0) Print
Expand All

Handling Large Objects Using CLR

The HandlingLOBUsingCLR sample for SQL Server demonstrates transferring large objects (LOBs) between SQL Server and a file system that is available to the server by using common language runtime (CLR) stored procedures. This sample demonstrates how to access files in server-side code, and then invoke both dynamic queries and stored procedures from CLR-based stored procedures. It also demonstrates how to unregister and register CLR methods and assemblies by using Transact-SQL.

To create and run this project the following the following software must be installed:

  • SQL Server or SQL Server Express. You can obtain SQL Server Express free of charge from the SQL Server Express Documentation and Samples Web site

  • The AdventureWorks database that is available at the SQL Server Developer Web site

  • .NET Framework SDK 2.0 or later or Microsoft Visual Studio 2005 or later. You can obtain .NET Framework SDK free of charge.

  • In addition, the following conditions must be met:

  • The SQL Server instance you are using must have CLR integration enabled.

  • In order to enable CLR integration, perform the following steps:

    Enabling CLR Integration

    • Execute the following Transact-SQL commands:

    sp_configure 'clr enabled', 1

    GO

    RECONFIGURE

    GO

    Note Note

    To enable CLR, you must have ALTER SETTINGS server level permission, which is implicitly held by members of the sysadmin and serveradmin fixed server roles.

  • The AdventureWorks database must be installed on the SQL Server instance you are using.

  • If you are not an administrator for the SQL Server instance you are using, you must have an administrator grant you CreateAssembly permission to complete the installation.

Create and run the sample by using the following instructions:

  1. Open a Visual Studio or .NET Framework command prompt.

  2. If necessary, create a directory for your sample. For this example, we will use C:\MySample.

  3. Since this example requires a signed assembly, create an asymmetric key by typing the command:

The following are the code listings for this sample.

C#

using System;
using System.Data;
using System.IO;
using System.Globalization;
using System.Data.SqlClient;
using Microsoft.SqlServer.Server;

    public sealed class LargeObjectBinary
    {
        //Recommended chunk size for processing large amounts of data
        private const int bufferSize = 4000;

        /// <summary>
        ///This class only contains static members, therefore it needs no public constructor.
        /// </summary>
        private LargeObjectBinary()
        {
        }


        /// <summary>
        /// Retrieves a thumbnail photograph from the database into a file assessible to the server.  
        /// </summary>
        /// <param name="photoId">Unique identifier for a product picture.</param>
        /// <param name="currentDirectory">Which folder to put the picture into.</param>
        /// <param name="fileName">What to call the picture in the specified folder.</param>
        public static void GetPhotoFromDB(Int32 photoId, string currentDirectory, string fileName)
        {
            SqlDataReader sqlReader = null;

            SqlConnection conn = new SqlConnection("context connection = true");
            conn.Open();
            
            SqlCommand sprocCommand = conn.CreateCommand();
            //Even though we are supply an int, it is a good habit to use parameters to insert
            //values into command text rather than using String.Format.  In the case of string parameters, it can
            //help prevent injection attacks.
            sprocCommand.CommandText = "SELECT ThumbNailPhoto FROM Production.ProductPhoto WHERE ProductPhotoID = @ProductPhotoID";
            sprocCommand.Parameters.Add("@ProductPhotoID", SqlDbType.Int);
            sprocCommand.Parameters[0].Value = photoId;

            //TODO: Is getting chunks the best way to retrieve LOB from the database?  Is there a limit?
            try
            {
                sqlReader = sprocCommand.ExecuteReader( //CommandBehavior.SequentialAccess
                    );
                if (sqlReader == null)
                {
                    LogError(currentDirectory, "ExecuteReader failed!");
                }
                else
                {
                    if (sqlReader.Read())
                    {
                        // Create a file to hold the output.
                        if (!Directory.Exists(currentDirectory))
                            Directory.CreateDirectory(currentDirectory);
                        fileName = currentDirectory + fileName;
                        using (FileStream fileStream = new FileStream(fileName,
                                                                      FileMode.
                                                                      OpenOrCreate,
                                                                      FileAccess.
                                                                      Write))
                        {
                            using (BinaryWriter binaryWriter =
                                                new BinaryWriter(
                                fileStream))
                            {
                                // The BLOB byte[] buffer to be filled by GetBytes.
                                byte[] outbyte = new byte[bufferSize];

                                // The starting position in the BLOB output.
                                long startIndex = 0;

                                // Read the bytes into outbyte[] and retain the number of bytes returned.
                                long retval = sqlReader.GetBytes(0, startIndex,
                                                                 outbyte, 0,
                                                                 bufferSize);

                                // Continue reading and writing while there are bytes beyond the size of the buffer.
                                while (retval == bufferSize)
                                {
                                    binaryWriter.Write(outbyte);

                                    // Reposition the start index to the end of the last buffer and fill the buffer.
                                    startIndex += bufferSize;
                                    retval = sqlReader.GetBytes(0, startIndex,
                                                                outbyte, 0,
                                                                bufferSize);
                                }

                                // Write the remaining buffer.
                                binaryWriter.Write(outbyte);
                                //TODO:  Shouldn't need to flush here because the close will do it for me?
                                //binaryWriter.Flush();
                            }
                        }
                    }
                    else
                        LogError(currentDirectory, "No row returned!");
                }
            }
            catch (SqlException e)
            {
                LogError(currentDirectory, String.Format(CultureInfo.InvariantCulture, "Unable to copy binary contents from database.  Error: {0}", e.ToString()));
            }
            finally
            {
                if (sqlReader != null)
                    sqlReader.Close();

                //dispose the conn
                if (conn != null)
                {
                    conn.Close();
                    conn.Dispose();
                }
            }
        }

        /// <summary>
        /// Saves a thumbnail picture into the database from a file accessible to the server.
        /// </summary>
        /// <param name="photoId">Unique identifier for a product picture.</param>
        /// <param name="currentDirectory">Which folder to get the picture from.</param>
        /// <param name="fileName">What the picture in the specified folder is called.</param>
        public static void PutPhotoIntoDB(Int32 photoId, string currentDirectory, string fileName)
        {
            //TODO: Is there a limit on how large the LOB can be?
            string fullFileName = currentDirectory + fileName;
            byte[] bytes = ReadFile(fullFileName);

            try
            {
                SqlConnection conn = new SqlConnection("context connection = true");
                conn.Open();

                SqlCommand sprocCommand = conn.CreateCommand();
                sprocCommand.CommandText = "dbo.usp_UpdateImage";
                sprocCommand.CommandType = CommandType.StoredProcedure;

                sprocCommand.Parameters.Add(new SqlParameter("@ProductPhotoID", SqlDbType.Int));
                // Add time to the short name because there is an unique constraint on this column.
                sprocCommand.Parameters[0].Value = photoId;
                sprocCommand.Parameters.Add(new SqlParameter("@ThumbNailPhoto", SqlDbType.VarBinary));
                sprocCommand.Parameters[1].Value = bytes;
                sprocCommand.ExecuteNonQuery();
            }
            catch (SqlException e)
            {
                LogError(currentDirectory, String.Format(CultureInfo.InvariantCulture, "Unable to update binary contents into the database.  Error: {0}", e.ToString()));
            }
        }

        /// <summary>
        /// Read the contents of a file and return the bytes.
        /// </summary>
        /// <param name="fileName">The name of the file to be read.</param>
        /// <returns></returns>
        private static byte[] ReadFile(string fileName)
        {
            // Open the file assuming the file is in ASCII format.
            using (BinaryReader binaryReader = new BinaryReader((Stream)File.OpenRead(fileName), System.Text.Encoding.ASCII))
            {
                long fileSize = binaryReader.BaseStream.Length;
                byte[] bytes = new Byte[fileSize];
                binaryReader.Read(bytes, 0, (int)fileSize);
                return bytes;
            }
        }

        /// <summary>
        ///Appends a message to a file accessible to the server.  When System.Diagnostics is available from
        /// CLR Sprocs this should be changed to use the event log.
        /// </summary>
        /// <param name="currentDirectory">Which folder the message log file resides in</param>
        /// <param name="errorMessage">The text to add to the message log file</param>
        private static void LogError(string currentDirectory, string errorMessage)
        {
            using (FileStream errorLogStream = new FileStream(currentDirectory + "error.log", FileMode.Append, FileAccess.Write))
            {
                using (StreamWriter errorLogWriter = new StreamWriter(errorLogStream))
                {
                    errorLogWriter.WriteLine(errorMessage);
                }
            }
        }
    }

Visual Basic

Imports Microsoft.SqlServer.Server
Imports Microsoft.VisualBasic
Imports System
Imports System.Collections
Imports System.Data
Imports System.Data.SqlClient
Imports System.Diagnostics
Imports System.Globalization
Imports System.IO
Imports System.Reflection

Public NotInheritable Class LargeObjectBinary
    'Recommended chunk size for processing large amounts of data
    Private Const bufferSize As Integer = 4000

    ''' <summary>
    '''    This class only contains static members, therefore it needs no public constructor.
    ''' </summary>
    Private Sub New()
    End Sub

    ''' <summary>
    ''' Retrieves a thumbnail photograph from the database into a file assessible to the server.  
    ''' </summary>
    ''' <param name="photoId">Unique identifier for a product picture.</param>
    ''' <param name="currentDirectory">Which folder to put the picture into.</param>
    ''' <param name="fileName">What to call the picture in the specified folder.</param>
    <Microsoft.SqlServer.Server.SqlProcedure()> _
    Public Shared Sub GetPhotoFromDB(ByVal photoId As Integer, _
        ByVal currentDirectory As String, ByVal fileName As String)
        Dim sqlReader As SqlDataReader = Nothing

        Dim conn As SqlConnection = New SqlConnection("context connection = true")
        conn.Open()

        Dim sprocCommand As SqlCommand = conn.CreateCommand()
        'Even though we are supply an int, it is a good habit to use parameters to insert
        'values into command text rather than using String.Format.  In the 
        'case of string parameters, it can help prevent injection attacks.
        sprocCommand.CommandText = "SELECT ThumbNailPhoto FROM Production.ProductPhoto " _
            & "WHERE ProductPhotoID = @ProductPhotoID"
        sprocCommand.Parameters.Add("@ProductPhotoID", SqlDbType.Int)
        sprocCommand.Parameters(0).Value = photoId

        'TODO: Is getting chunks the best way to retrieve LOB from the database?  Is there a limit?
        Try
            sqlReader = sprocCommand.ExecuteReader() 'CommandBehavior.SequentialAccess
            If sqlReader Is Nothing Then
                LogError(currentDirectory, "ExecuteReader failed!")
            Else
                If sqlReader.Read() Then
                    ' Create a file to hold the output.
                    If (Not Directory.Exists(currentDirectory)) Then
                        Directory.CreateDirectory(currentDirectory)
                    End If

                    fileName = currentDirectory + fileName
                    Dim fileStream As New FileStream(fileName, FileMode.OpenOrCreate, FileAccess.Write)
                    Try
                        Dim binaryWriter As New BinaryWriter(fileStream)
                        Try
                            ' The BLOB byte() buffer to be filled by GetBytes.
                            Dim outbyte(bufferSize) As Byte

                            ' The starting position in the BLOB output.
                            Dim startIndex As Long = 0

                            ' Read the bytes into outbyte() and retain the number of bytes returned.
                            Dim retval As Long = sqlReader.GetBytes(0, startIndex, outbyte, 0, bufferSize)

                            ' Continue reading and writing while there are 
                            ' bytes beyond the size of the buffer.
                            While retval = bufferSize
                                binaryWriter.Write(outbyte)

                                ' Reposition the start index to the end of 
                                ' the last buffer and fill the buffer.
                                startIndex += bufferSize
                                retval = sqlReader.GetBytes(0, startIndex, outbyte, 0, bufferSize)
                            End While

                            ' Write the remaining buffer.
                            binaryWriter.Write(outbyte)
                        Finally
                            binaryWriter.Close()
                        End Try
                    Finally
                        fileStream.Close()
                    End Try 'binaryWriter.Flush();
                Else
                    LogError(currentDirectory, "No row returned!")
                End If
            End If
        Catch e As SqlException
            LogError(currentDirectory, String.Format(CultureInfo.InvariantCulture, _
                "Unable to copy binary contents from database.  Error: {0}", e.ToString()))
        Finally
            If Not (sqlReader Is Nothing) Then
                sqlReader.Close()
            End If
            'dispoae the conn
            If Not (conn Is Nothing) Then
                conn.Close()
                conn.Dispose()
            End If
        End Try
    End Sub

    ''' <summary>
    ''' Saves a thumbnail picture into the database from a file accessible to the server.
    ''' </summary>
    ''' <param name="photoId">Unique identifier for a product picture.</param>
    ''' <param name="currentDirectory">Which folder to get the picture from.</param>
    ''' <param name="fileName">What the picture in the specified folder is called.</param>
    <Microsoft.SqlServer.Server.SqlProcedure()> _
    Public Shared Sub PutPhotoIntoDB(ByVal photoId As Integer, _
        ByVal currentDirectory As String, ByVal fileName As String)
        'TODO: Is there a limit on how large the LOB can be?
        Dim fullFileName As String = currentDirectory + fileName
        Dim bytes As Byte() = ReadFile(fullFileName)

        Try
            Dim conn As SqlConnection = New SqlConnection("context connection = true")
            conn.Open()

            Dim sprocCommand As SqlCommand = conn.CreateCommand()
            sprocCommand.CommandText = "dbo.usp_UpdateImage"
            sprocCommand.CommandType = CommandType.StoredProcedure

            sprocCommand.Parameters.Add(New SqlParameter("@ProductPhotoID", SqlDbType.Int))
            ' Add time to the short name because there is an unique constraint on this column.
            sprocCommand.Parameters(0).Value = photoId
            sprocCommand.Parameters.Add(New SqlParameter("@ThumbNailPhoto", SqlDbType.VarBinary))
            sprocCommand.Parameters(1).Value = bytes
            sprocCommand.ExecuteNonQuery()
        Catch e As SqlException
            LogError(currentDirectory, String.Format(CultureInfo.InvariantCulture, _
                "Unable to update binary contents into the database.  Error: {0}", e.ToString()))
        End Try
    End Sub

    ''' <summary>
    ''' Read the contents of a file and return the bytes.
    ''' </summary>
    ''' <param name="fileName">The name of the file to be read.</param>
    ''' <returns></returns>
    Private Shared Function ReadFile(ByVal fileName As String) As Byte()
        ' Open the file assuming the file is in ASCII format.
        'Dim binaryReader As New BinaryReader(CType(File.OpenRead(fileName), Stream), System.Text.Encoding.ASCII)
        'Try
        '    Dim fileSize As Long = binaryReader.BaseStream.Length
        '    Dim bytes() As Byte = New Byte(CType(fileSize, Integer)) {}
        '    binaryReader.Read(bytes, 0, CType(fileSize, Integer))
        '    Return bytes
        'Finally
        '    binaryReader.Close()
        'End Try

        Dim binaryReader As New BinaryReader(CType(File.OpenRead(fileName), Stream), System.Text.Encoding.ASCII)
        Using (binaryReader)
            Dim fileSize As Long = binaryReader.BaseStream.Length
            Dim bytes() As Byte = New Byte(CType(fileSize, Integer)) {}
            binaryReader.Read(bytes, 0, CType(fileSize, Integer))
            Return bytes
        End Using

    End Function

    ''' <summary>
    '''        Appends a message to a file accessible to the server.  When System.Diagnostics is available from
    '''        CLR Sprocs this should be changed to use the event log.
    ''' </summary>
    ''' <param name="currentDirectory">Which folder the message log file resides in</param>
    ''' <param name="errorMessage">The text to add to the message log file</param>
    Private Shared Sub LogError(ByVal currentDirectory As String, ByVal errorMessage As String)
        Dim errorLogStream As New FileStream(currentDirectory + "error.log", FileMode.Append, FileAccess.Write)
        Try
            Dim errorLogWriter As New StreamWriter(errorLogStream)
            Try
                errorLogWriter.WriteLine(errorMessage)
            Finally
                errorLogWriter.Close()
            End Try
        Finally
            errorLogStream.Close()
        End Try
    End Sub
End Class

This is the Transact-SQL installation script (Install.sql), which deploys the assembly and creates the stored procedures and security objects required by this example.

USE AdventureWorks
GO

-- Drop procedures defined in this script if they exist

IF EXISTS (SELECT * FROM sys.procedures WHERE [name] = N'usp_UpdateImage')
DROP PROCEDURE [dbo].[usp_UpdateImage];
GO

IF EXISTS (SELECT * FROM sys.procedures WHERE [name] = N'GetPhotoFromDB')
DROP PROCEDURE [dbo].[GetPhotoFromDB];
GO

IF EXISTS (SELECT * FROM sys.procedures WHERE [name] = N'PutPhotoIntoDB')
DROP PROCEDURE [dbo].[PutPhotoIntoDB];
GO

-- If the assembly we want to add already exists, drop it.

IF EXISTS (SELECT [name] FROM sys.assemblies WHERE [name] = N'HandlingLOBUsingCLR')
DROP ASSEMBLY HandlingLOBUsingCLR;
GO
use master
go
IF EXISTS (SELECT * FROM sys.server_principals WHERE [name] = 'ExternalSample_Login')
DROP LOGIN ExternalSample_Login;
GO

IF EXISTS (SELECT * FROM sys.asymmetric_keys WHERE [name] = 'ExternalSample_Key')
DROP ASYMMETRIC KEY ExternalSample_Key;
GO

--Before we register the assembly to SQL Server, we must arrange for the appropriate permissions.
--Assemblies with unsafe or external_access permissions can only be registered and operate correctly
--if either the database trustworthy bit is set or if the assembly is signed with a key,
--that key is registered with SQL Server, a server principal is created from that key,
--and that principal is granted the external access or unsafe assembly permission.  We choose
--the latter approach as it is more granular, and therefore safer.  You should never
--register an assembly with SQL Server (especially with external_access or unsafe permissions) without
--thoroughly reviewing the source code of the assembly to make sure that its actions 
--do not pose an operational or security risk for your site.

DECLARE @SamplesPath nvarchar(1024)
-- You may need to modify the value of the this variable if you have installed the sample someplace other than the default location.
set @SamplesPath = N'C:\MySample\'

EXEC('CREATE ASYMMETRIC KEY ExternalSample_Key FROM EXECUTABLE FILE = ''' + @SamplesPath + 'HandlingLOBUsingCLR.dll'';');
CREATE LOGIN ExternalSample_Login FROM ASYMMETRIC KEY ExternalSample_Key
GRANT EXTERNAL ACCESS ASSEMBLY TO ExternalSample_Login
GO

USE AdventureWorks
GO
DECLARE @SamplesPath nvarchar(1024)
-- You may need to modify the value of the this variable if you have installed the sample someplace other than the default location.
set @SamplesPath = N'C:\MySample\'
CREATE ASSEMBLY HandlingLOBUsingCLR
FROM @SamplesPath + 'HandlingLOBUsingCLR.dll'
WITH permission_set = external_access;
GO

-- Register the CLR method for retrieving thumbnail photos from the ProductPhoto table

CREATE PROCEDURE [dbo].[GetPhotoFromDB]
(
    @ProductPhotoID int
    ,@CurrentDirectory nvarchar(1024)
    ,@FileName nvarchar(1024)   
)
AS EXTERNAL NAME HandlingLOBUsingCLR.[LargeObjectBinary].GetPhotoFromDB;
GO

-- Register the CLR method for storing thumbnail photos into the ProductPhoto table

CREATE PROCEDURE [dbo].[PutPhotoIntoDB]
(
    @ProductPhotoID int
    ,@CurrentDirectory nvarchar(1024)
    ,@FileName nvarchar(1024)   
)
AS EXTERNAL NAME HandlingLOBUsingCLR.[LargeObjectBinary].PutPhotoIntoDB;
GO


-- Add a helper T-SQL method which does the actual work of updating the row

CREATE PROCEDURE [dbo].[usp_UpdateImage]
/* **********************************************************************************
   Date:    April 22, 2003
   Purpose: Change a thumbnail picture stored in the ProductPhoto table.
   ********************************************************************************** */
    @ProductPhotoID int
    ,@ThumbNailPhoto AS VARBINARY(max)
AS
BEGIN
    SET NOCOUNT ON;

BEGIN TRY
    UPDATE Production.ProductPhoto 
        SET ThumbNailPhoto = @ThumbNailPhoto
        WHERE ProductPhotoID = @ProductPhotoID;
    IF(@@ROWCOUNT < 1)
        RAISERROR ('Update failed.', 16, 1);
END TRY
BEGIN CATCH
        SELECT 
ERROR_NUMBER() AS ErrorNumber,
ERROR_SEVERITY() AS ErrorSeverity,
ERROR_STATE() as ErrorState,
ERROR_PROCEDURE() as ErrorProcedure,
ERROR_LINE() as ErrorLine,
ERROR_MESSAGE() as ErrorMessage;
        RAISERROR ('Update failed.', 16, 1);
END CATCH;
END  -- END of sp_InsertDocument
GO

The following Transact-SQL (test.sql) tests the example by exercising the stored procedures.

USE AdventureWorks
GO

EXEC GetPhotoFromDB 70, 'C:\Temp\', 'test6.gif';
go

EXEC PutPhotoIntoDB 70, 'C:\Temp\', 'test6.gif';
go

The following Transact-SQL removes the assembly, login, key and stored procedures from the database.

USE AdventureWorks
GO

-- Drop procedures defined in the install script if they exist

IF EXISTS (SELECT * FROM sys.procedures WHERE [name] = N'usp_UpdateImage')
DROP PROCEDURE [dbo].[usp_UpdateImage];
GO

IF EXISTS (SELECT * FROM sys.procedures WHERE [name] = N'GetPhotoFromDB')
DROP PROCEDURE [dbo].[GetPhotoFromDB];
GO

IF EXISTS (SELECT * FROM sys.procedures WHERE [name] = N'PutPhotoIntoDB')
DROP PROCEDURE [dbo].[PutPhotoIntoDB];
GO

-- If the assembly exists, drop it.

IF EXISTS (SELECT [name] FROM sys.assemblies WHERE [name] = N'HandlingLOBUsingCLR')
DROP ASSEMBLY HandlingLOBUsingCLR;
GO

USE master
GO

IF EXISTS (SELECT * FROM sys.server_principals WHERE [name] = 'ExternalSample_Login')
DROP LOGIN ExternalSample_Login;
GO

IF EXISTS (SELECT * FROM sys.asymmetric_keys WHERE [name] = 'ExternalSample_Key')
DROP ASYMMETRIC KEY ExternalSample_Key;
GO
USE AdventureWorks
GO

Community Additions

ADD
Show:
© 2014 Microsoft