Question

我正在尝试将存储在sql server中的内容作为varbinary（max）流式传输到客户端。我能够使它工作，但连接将保持打开，直到垃圾收集。如果在返回结果之前丢弃连接，读取器或蒸汽，则会导致对象处理错误。

我希望避免将数据复制到内存中（因为它可能很大），同时在完成后正确处理对象。什么是实现这两个目标的最佳方式。

如果相关，我使用的是.NET Core 2.0。

更新：这不是其他人（How do I dispose my filestream when implementing a file download in ASP.NET?）的重复，因为我不是在问如何处理流，而是如何处理相关的连接对象。我的问题更多的是确保连接对象被处理的正确方法

下面的代码成功返回结果，但保留了一个非处理连接：

public async Task<IActionResult> DownloadFile(Guid FileId)
{
    var connection = new SqlConnection(DatabaseService.ConnectionString);

    await connection.OpenAsync();
    var command = connection.CreateCommand();

    command.CommandText = "select FileName, FileContent from Files where FileId=@FileId";
    command.CommandType = System.Data.CommandType.Text;
    command.Parameters.AddWithValue("@FileId", FileId);

    var reader = await command.ExecuteReaderAsync(System.Data.CommandBehavior.SequentialAccess | System.Data.CommandBehavior.SingleRow);

    if (!await reader.ReadAsync())
        return NotFound();
    var attachmentName = Convert.ToString(reader[0]);

    var stream = reader.GetStream(1);

    var response = File(stream, "application/octet-stream", attachmentName);
    return response;
}

下面的代码处理了该对象，但由于首先处理了该内容，因此无法对内容进行流式传输

public async Task<IActionResult> DownloadFile(Guid FileId)
{
    using (var connection = new SqlConnection(DatabaseService.ConnectionString))
    {

        await connection.OpenAsync();
        using (var command = connection.CreateCommand())
        {

            command.CommandText = "select FileName, FileContent from Files where FileId=@FileId";
            command.CommandType = System.Data.CommandType.Text;
            command.Parameters.AddWithValue("@FileId", FileId);

            using (var reader = await command.ExecuteReaderAsync(System.Data.CommandBehavior.SequentialAccess | System.Data.CommandBehavior.SingleRow))
            {

                if (!await reader.ReadAsync())
                    return NotFound();
                var attachmentName = Convert.ToString(reader[0]);

                using (var stream = reader.GetStream(1))
                {

                    var response = File(stream, "application/octet-stream", attachmentName);
                    return response;
                }
            }
        }
    }
}

Answer 1

大卫布朗的回答给了我相关信息。我需要使用HttpContext.Response.RegisterForDispose();注册一次性组件。这可确保在请求完成后处理它。

以下是更新后的代码

public async Task<IActionResult> DownloadFile(Guid FileId)
{
    var connection = new SqlConnection(DatabaseService.ConnectionString);
    HttpContext.Response.RegisterForDispose(connection);

    await connection.OpenAsync();
    var command = connection.CreateCommand();
    HttpContext.Response.RegisterForDispose(command);

    command.CommandText = "select FileName, FileContent from Files where FileId=@FileId";
    command.CommandType = System.Data.CommandType.Text;
    command.Parameters.AddWithValue("@FileId", FileId);

    var reader = await command.ExecuteReaderAsync(System.Data.CommandBehavior.SequentialAccess | System.Data.CommandBehavior.SingleRow);
    HttpContext.Response.RegisterForDispose(reader);

    if (!await reader.ReadAsync())
        return NotFound();
    var attachmentName = Convert.ToString(reader[0]);

    var stream = reader.GetStream(1);
    HttpContext.Response.RegisterForDispose(stream);

    var response = File(stream, "application/octet-stream", attachmentName);
    return response;
}

如果其他人有同样的问题我添加了这个答案

Answer 2

只需在客户端使用响应后处理SqlConnection。参见：

https://andrewlock.net/four-ways-to-dispose-idisposables-in-asp-net-core/

https://www.strathweb.com/2017/03/disposing-resources-at-the-end-of-asp-net-core-request/

ASP.NET MVC中的SQL Server流文件输出和处理连接

2 个答案: