使用 UPDATETEXT 搭配二進位資料 (ADO.NET)

發行項
05/20/2011

在 SQL Server 2005 之前的 SQL Server 版本中，使用二進位大型物件 (BLOB) 的選項有所限制。根據資料庫中之欄位型別的不同，您可以利用字串值或位元組陣列插入或更新欄位，將 BLOB 寫入資料庫。不過，BLOB 可能相當大，因此在做為單一值寫入時可能會耗用許多系統記憶體，使得應用程式效能降低。

在寫入 BLOB 值時，為了減少記憶體的使用量，一般的做法是以「區塊」將 BLOB 寫入資料庫。以這種方式將 BLOB 寫入資料庫的過程取決於資料庫的容量。

Transact-SQL UPDATETEXT 範例

下列範例示範如何以區塊將 BLOB 寫入 SQL Server。該範例會將包含員工影像的新資料錄 (亦即 BLOB) 加入 Northwind 資料庫的 Employees 資料表中。該範例也會使用 SQL Server 的 UPDATETEXT 函式，將新加入員工的影像以指定大小區塊寫入 Photo 欄位。

UPDATETEXT 函式需要即將更新之 BLOB 欄位的指標。在這個範例中，加入新員工資料錄時，系統會呼叫 SQL Server TEXTPTR 函式，將新資料錄 Photo 欄位的指標傳回。傳回的指標值會被當做輸出參數傳回。該範例中的程式碼會保留這個指標，並在附加資料區塊時將它傳給 UPDATETEXT。

下列範例顯示用於插入新員工資料錄和保留 Photo 欄位指標的 Transact-SQL (其中 @Identity 和 @Pointer 識別為 SqlCommand 的輸出參數)。

INSERT INTO Employees (LastName, FirstName, Title, HireDate, ReportsTo, Photo) 
  Values(@LastName, @FirstName, @Title, @HireDate, @ReportsTo, 0x0)
SELECT @Identity = SCOPE_IDENTITY()
SELECT @Pointer = TEXTPTR(Photo) FROM Employees WHERE EmployeeID = @Identity

請注意，Photo 欄位中會插入 0x0 (null) 的初始值。這樣可確保擷取到新插入資料錄 Photo 欄位的指標值。然而，Null 值卻不會影響附加的資料區塊。

在保留了新插入資料錄 Photo 欄位的指標後，該範例可以接著使用 SQL Server 的 UPDATETEXT 函式將資料區塊附加至 BLOB 欄位。 UPDATETEXT 函式中將輸入欄位識別項 (Employees.Photo)、BLOB 欄位指標、位移值 (代表要寫入目前區塊之 BLOB 內的位置)，以及附加的資料區塊。下列程式碼範例顯示 UPDATETEXT 函式的語法 (其中 @Pointer、@Offset, 和 @Bytes 是做為 SqlCommand 的輸入參數)。

UPDATETEXT Employees.Photo @Pointer @Offset 0 @Bytes

位移值是由記憶體緩衝區大小來決定，而緩衝區大小是根據應用程式的需求來決定。緩衝區越大，寫入 BLOB 的速度就越快，但所使用的系統記憶體也較多。在這個範例中使用較小的緩衝區，僅 128 位元組。第一個資料區塊的位移值是從 0 開始，之後以每個連續區塊的緩衝區大小來遞增。

ADO.NET 更新範例

這個範例會從提供的路徑上以區塊擷取員工相片。每個區塊會依照指定的緩衝區大小讀入位元組陣列中。之後，系統會將這個位元組陣列設定為 SqlCommand 的 @Bytes 輸入參數值。接著更新 @Offset 參數值，並執行 SqlCommand，將目前位元組區塊附加至員工資料錄的 Photo 欄位。

Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.IO

Public Class EmployeeData
    Public Shared Sub Main()
        Dim hireDate As DateTime = DateTime.Parse("4/27/98")
        Dim newID As Integer = _
            AddEmployee("Smith", "John", "Sales Representative", hireDate, 5, "smith.bmp")
        Console.WriteLine("New Employee added. EmployeeID = " & newID)
    End Sub

    Public Shared Function AddEmployee(ByVal lastName As String, _
        ByVal firstName As String, ByVal title As String, ByVal hireDate As DateTime, _
        ByVal reportsTo As Integer, ByVal photoFilePath As String) As Integer

        Using connection As SqlConnection = New SqlConnection( _
        "Data Source=(local);Integrated Security=true;Initial Catalog=Northwind;")

            Dim addEmp As SqlCommand = New SqlCommand( _
                "INSERT INTO Employees (LastName, FirstName, Title, HireDate, ReportsTo, Photo) " & _
            "Values(@LastName, @FirstName, @Title, @HireDate, @ReportsTo, 0x0);" & _
            "SELECT @Identity = SCOPE_IDENTITY();" & _
            "SELECT @Pointer = TEXTPTR(Photo) FROM Employees WHERE EmployeeID = @Identity", _
            connection)

            addEmp.Parameters.Add("@LastName", SqlDbType.NVarChar, 20).Value = lastName
            addEmp.Parameters.Add("@FirstName", SqlDbType.NVarChar, 10).Value = firstName
            addEmp.Parameters.Add("@Title", SqlDbType.NVarChar, 30).Value = title
            addEmp.Parameters.Add("@HireDate", SqlDbType.DateTime).Value = hireDate
            addEmp.Parameters.Add("@ReportsTo", SqlDbType.Int).Value = reportsTo

            Dim idParm As SqlParameter = addEmp.Parameters.Add("@Identity", SqlDbType.Int)
            idParm.Direction = ParameterDirection.Output
            Dim ptrParm As SqlParameter = addEmp.Parameters.Add("@Pointer", SqlDbType.Binary, 16)
            ptrParm.Direction = ParameterDirection.Output

            connection.Open()

            addEmp.ExecuteNonQuery()

            Dim newEmpID As Integer = CType(idParm.Value, Integer)

            StorePhoto(photoFilePath, ptrParm.Value, connection)

            Return newEmpID
        End Using
    End Function

    Public Shared Sub StorePhoto(ByVal fileName As String, _
        ByVal pointer As Byte(), ByVal connection As SqlConnection)

        ' The size of the "chunks" of the image.
        Dim bufferLen As Integer = 128

        Dim appendToPhoto As SqlCommand = New SqlCommand( _
            "UPDATETEXT Employees.Photo @Pointer @Offset 0 @Bytes", _
            connection)

        Dim ptrParm As SqlParameter = appendToPhoto.Parameters.Add( _
            "@Pointer", SqlDbType.Binary, 16)
        ptrParm.Value = pointer
        Dim photoParm As SqlParameter = appendToPhoto.Parameters.Add( _
            "@Bytes", SqlDbType.Image, bufferLen)
        Dim offsetParm As SqlParameter = appendToPhoto.Parameters.Add( _
            "@Offset", SqlDbType.Int)
        offsetParm.Value = 0

        '' Read the image in and write it to the database 128 (bufferLen) bytes 
        '' at a time. Tune bufferLen for best performance. Larger values 
        '' write faster, but use more system resources.
        Dim fs As FileStream = New FileStream(fileName, FileMode.Open, FileAccess.Read)
        Dim br As BinaryReader = New BinaryReader(fs)

        Dim buffer() As Byte = br.ReadBytes(bufferLen)
        Dim offset_ctr As Integer = 0

        Do While buffer.Length > 0
            photoParm.Value = buffer
            appendToPhoto.ExecuteNonQuery()
            offset_ctr += bufferLen
            offsetParm.Value = offset_ctr
            buffer = br.ReadBytes(bufferLen)
        Loop

        br.Close()
        fs.Close()
    End Sub
End Class

using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;

public class EmployeeData
{
    public static void Main()
    {
        DateTime hireDate = DateTime.Parse("4/27/98");
        int newID = AddEmployee("Smith", "John", "Sales Representative",
            hireDate, 5, "smith.bmp");
        Console.WriteLine("New Employee added. EmployeeID = " + newID);
    }

    public static int AddEmployee(string lastName, string firstName,
        string title, DateTime hireDate, int reportsTo, string photoFilePath)
    {
        using (SqlConnection connection = new SqlConnection(
            "Data Source=(local);Integrated Security=true;Initial Catalog=Northwind;"))
        {

            SqlCommand addEmp = new SqlCommand(
                "INSERT INTO Employees (LastName, FirstName, Title, HireDate, ReportsTo, Photo) " +
                "Values(@LastName, @FirstName, @Title, @HireDate, @ReportsTo, 0x0);" +
                "SELECT @Identity = SCOPE_IDENTITY();" +
                "SELECT @Pointer = TEXTPTR(Photo) FROM Employees WHERE EmployeeID = @Identity", 
                connection);

            addEmp.Parameters.Add("@LastName", SqlDbType.NVarChar, 20).Value = lastName;
            addEmp.Parameters.Add("@FirstName", SqlDbType.NVarChar, 10).Value = firstName;
            addEmp.Parameters.Add("@Title", SqlDbType.NVarChar, 30).Value = title;
            addEmp.Parameters.Add("@HireDate", SqlDbType.DateTime).Value = hireDate;
            addEmp.Parameters.Add("@ReportsTo", SqlDbType.Int).Value = reportsTo;

            SqlParameter idParm = addEmp.Parameters.Add("@Identity", SqlDbType.Int);
            idParm.Direction = ParameterDirection.Output;
            SqlParameter ptrParm = addEmp.Parameters.Add("@Pointer", SqlDbType.Binary, 16);
            ptrParm.Direction = ParameterDirection.Output;

            connection.Open();

            addEmp.ExecuteNonQuery();

            int newEmpID = (int)idParm.Value;

            StorePhoto(photoFilePath, (byte[])ptrParm.Value, connection);

            return newEmpID;
        }
    }

    public static void StorePhoto(string fileName, byte[] pointer, 
        SqlConnection connection)
    {
        // The size of the "chunks" of the image.
        int bufferLen = 128;  

        SqlCommand appendToPhoto = new SqlCommand(
            "UPDATETEXT Employees.Photo @Pointer @Offset 0 @Bytes", 
            connection);

        SqlParameter ptrParm = appendToPhoto.Parameters.Add(
            "@Pointer", SqlDbType.Binary, 16);
        ptrParm.Value = pointer;
        SqlParameter photoParm = appendToPhoto.Parameters.Add(
            "@Bytes", SqlDbType.Image, bufferLen);
        SqlParameter offsetParm = appendToPhoto.Parameters.Add(
            "@Offset", SqlDbType.Int);
        offsetParm.Value = 0;

        // Read the image in and write it to the database 128 (bufferLen) bytes at a time.
        // Tune bufferLen for best performance. Larger values write faster, but
        // use more system resources.
        FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
        BinaryReader br = new BinaryReader(fs);

        byte[] buffer = br.ReadBytes(bufferLen);
        int offset_ctr = 0;

        while (buffer.Length > 0)
        {
            photoParm.Value = buffer;
            appendToPhoto.ExecuteNonQuery();
            offset_ctr += bufferLen;
            offsetParm.Value = offset_ctr;
            buffer = br.ReadBytes(bufferLen);
        }

        br.Close();
        fs.Close();
    }
}

請參閱

概念

SQL Server 資料型別對應 (ADO.NET)

其他資源

SQL Server 二進位和大數值資料 (ADO.NET)

擷取和修改 ADO.NET 中的資料

共用方式為

使用 UPDATETEXT 搭配二進位資料 (ADO.NET)

Transact-SQL UPDATETEXT 範例

ADO.NET 更新範例

請參閱

概念

其他資源

其他資源