从CLR存储过程中访问Sql FILESTREAM [英] Accessing Sql FILESTREAM from within a CLR stored procedure

问题描述

我正在尝试从CLR存储过程访问Sql文件流.我已经建立了一个非常简单的数据库，其中包含一个包含文件流列的表.我可以使用一个简单的控制台应用程序成功读取文件流.这是失败的proc的一些示例代码:

I'm trying to access a Sql filestream from a CLR stored procedure. I've set up a very simple database with a single table which includes a filestream column. I can successfully read from the filestream using a simple console app. Here's some example code for the proc that fails:

[SqlProcedure]
public static void GetDataFromFileStream(string path, out int data)
{
    using (var connection = new SqlConnection("context connection=true"))
    {
        connection.Open();

        var transaction = connection.BeginTransaction();

        var transactionContext = GetTransactionContext(connection, transaction);

        // the following line throws an exception
        var sqlFileStream = new SqlFileStream(path, transactionContext, FileAccess.Read);

        var buffer = new byte[4];
        sqlFileStream.Read(buffer, 0, 4);

        data = BitConverter.ToInt32(buffer, 0);
    }
}

private static byte[] GetTransactionContext(SqlConnection connection, SqlTransaction transaction)
{
    using (var cmd = connection.CreateCommand())
    {
        const string myGetTxContextQuery = "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()";
        cmd.CommandText = myGetTxContextQuery;
        cmd.CommandTimeout = 60;
        cmd.CommandType = CommandType.Text;
        cmd.Transaction = transaction;
        return (byte[])cmd.ExecuteScalar();
    }
}

尝试构造SqlFileStream实例时抛出异常:

An exception is thrown when trying to construct the SqlFileStream instance:

发生System.ComponentModel.Win32Exception Message =不支持该请求" Source ="System.Data" 错误代码= -2147467259 NativeErrorCode = 50

System.ComponentModel.Win32Exception occurred Message="The request is not supported" Source="System.Data" ErrorCode=-2147467259 NativeErrorCode=50

有人知道我在做什么错吗?

Anyone know what I'm doing wrong?

推荐答案

由于上述问题，我无法使用SqlFileStream直接从CLR内部访问文件流.我最终采用的解决方案是使用SQL存储过程来获取所需的文件流数据的子集.尽管在某些情况下这不是特别有效，但对于我的应用程序来说已经足够了

I was unable to use SqlFileStream to access the filestreams directly from within the CLR (because of the problems identified above). The solution I eventually adopted was to use a SQL stored procedure to get hold of the subset of filestream data I needed. Although this is not particularly efficient in some scenarios, it sufficed for my application

    CREATE PROC ReadFromFilestream
    (
        @pfilestreamGUID    UNIQUEIDENTIFIER,
        @pOffsetIntoData    INT,
        @pLengthOfData      INT,
        @pData              VARBINARY(MAX) OUTPUT
    )
    AS
    BEGIN;
        SELECT @pData  = SUBSTRING(ValueData, @pOffsetIntoData, @pLengthOfData)
          FROM [MESL].DataStream
         WHERE DataStreamGUID = @pfilestreamGUID;
    END;

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