c# - System.OutOfMemoryException - 当 Entity Framework 正在查询 Varbinary 类型的过大数据时

Question

我正在尝试查询包含文件 (1,2 Gb) 的 varbinary 列。

我正在使用 Entity Framework 。见下文:

要测试的数据库

CREATE TABLE [dbo].[BIGDATA]
(
    [id] [bigint] IDENTITY(1,1) NOT NULL,
    [BIGDATA] [varbinary](max) NULL, 

    CONSTRAINT [PK_BIGDATA] PRIMARY KEY CLUSTERED ([id] ASC) 
) ON [PRIMARY]

要测试的数据(任何 1 Gb 的文件)

INSERT INTO [dbo].[BIGDATA]([BIGDATA])
VALUES
   ((SELECT BulkColumn FROM OPENROWSET(BULK N'C:\BigTest.txt', SINGLE_BLOB) AS Document))

Controller 下载文件

public FileResult Download()
{
        try
        {
            var context = new Models.ELOGTESTEEntities();

            var idArquivo = Convert.ToInt32(1);

            // The problem is here, when trying send command to SQL Server to read register
            var arquivo = (from item in context.BIGDATA
                           where item.id.Equals(idArquivo)
                           select item).Single();
            var mimeType = ".txt";              

            byte[] bytes = System.Text.Encoding.GetEncoding("iso-8859-8").GetBytes("BigTest.txt");
            return File(arquivo.BIGDATA1, mimeType, System.Text.Encoding.UTF8.GetString(bytes));
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

我可以使用 Select * From BigData 在 SQL Server 上正常查询。

但是，在 Entity Framework (或使用 ADO 的命令)中我得到了这个异常:

System.OutOfMemoryException

有人知道如何解决这个问题吗？

Answer 1

哇，好大的数据。我真的认为您不需要使用 EF 来获取这些数据，而是使用好的 'ol SqlDataReader。

考虑到您的 .net 4.0 限制，我发现了一个自定义实现，可以从大量 varbinary 列流式读取。除了检查代码并确保其中没有 .net 4.5 快捷方式外，我不能对此给予任何赞誉:

http://www.syntaxwarriors.com/2013/stream-varbinary-data-to-and-from-mssql-using-csharp/

Mods - 让我知道是否应该将类似的内容复制/粘贴到答案中，因为原始 URL 可能不会持久存在。

编辑:以下是链接中的代码，以防 URL 消失:

用法:

// reading and returning data to the client
VarbinaryStream filestream = new VarbinaryStream(
                                DbContext.Database.Connection.ConnectionString, 
                                "FileContents", 
                                "Content", 
                                "ID", 
                                (int)filepost.ID, 
                                true);

// Do what you want with the stream here.

代码:

public class VarbinaryStream : Stream
{
    private SqlConnection _Connection;

    private string  _TableName;
    private string  _BinaryColumn;
    private string  _KeyColumn;
    private int     _KeyValue;

    private long    _Offset;

    private SqlDataReader _SQLReader;
    private long _SQLReadPosition;

    private bool _AllowedToRead = false;

    public VarbinaryStream(
        string ConnectionString,
        string TableName,
        string BinaryColumn,
        string KeyColumn,
        int KeyValue,
        bool AllowRead = false)
    {
        // create own connection with the connection string.
        _Connection = new SqlConnection(ConnectionString);

        _TableName = TableName;
        _BinaryColumn = BinaryColumn;
        _KeyColumn = KeyColumn;
        _KeyValue = KeyValue;


        // only query the database for a result if we are going to be reading, otherwise skip.
        _AllowedToRead = AllowRead;
        if (_AllowedToRead == true)
        {
            try
            {
                if (_Connection.State != ConnectionState.Open)
                    _Connection.Open();

                SqlCommand cmd = new SqlCommand(
                                @"SELECT TOP 1 [" + _BinaryColumn + @"]
                                FROM [dbo].[" + _TableName + @"]
                                WHERE [" + _KeyColumn + "] = @id",
                            _Connection);

                cmd.Parameters.Add(new SqlParameter("@id", _KeyValue));

                _SQLReader = cmd.ExecuteReader(
                    CommandBehavior.SequentialAccess |
                    CommandBehavior.SingleResult |
                    CommandBehavior.SingleRow |
                    CommandBehavior.CloseConnection);

                _SQLReader.Read();
            }
            catch (Exception e)
            {
                // log errors here
            }
        }
    }

    // this method will be called as part of the Stream ímplementation when we try to write to our VarbinaryStream class.
    public override void Write(byte[] buffer, int index, int count)
    {
        try
        {
            if (_Connection.State != ConnectionState.Open)
                _Connection.Open();

            if (_Offset == 0)
            {
                // for the first write we just send the bytes to the Column
                SqlCommand cmd = new SqlCommand(
                                            @"UPDATE [dbo].[" + _TableName + @"]
                                                SET [" + _BinaryColumn + @"] = @firstchunk 
                                            WHERE [" + _KeyColumn + "] = @id",
                                        _Connection);

                cmd.Parameters.Add(new SqlParameter("@firstchunk", buffer));
                cmd.Parameters.Add(new SqlParameter("@id", _KeyValue));

                cmd.ExecuteNonQuery();

                _Offset = count;
            }
            else
            {
                // for all updates after the first one we use the TSQL command .WRITE() to append the data in the database
                SqlCommand cmd = new SqlCommand(
                                        @"UPDATE [dbo].[" + _TableName + @"]
                                            SET [" + _BinaryColumn + @"].WRITE(@chunk, NULL, @length)
                                        WHERE [" + _KeyColumn + "] = @id",
                                     _Connection);

                cmd.Parameters.Add(new SqlParameter("@chunk", buffer));
                cmd.Parameters.Add(new SqlParameter("@length", count));
                cmd.Parameters.Add(new SqlParameter("@id", _KeyValue));

                cmd.ExecuteNonQuery();

                _Offset += count;
            }
        }
        catch (Exception e)
        {
            // log errors here
        }
    }

    // this method will be called as part of the Stream ímplementation when we try to read from our VarbinaryStream class.
    public override int Read(byte[] buffer, int offset, int count)
    {
        try
        {
            long bytesRead = _SQLReader.GetBytes(0, _SQLReadPosition, buffer, offset, count);
            _SQLReadPosition += bytesRead;
            return (int)bytesRead;
        }
        catch (Exception e)
        {
            // log errors here
        }
        return -1;
    }
    public override bool CanRead
    {
        get { return _AllowedToRead; }
    }

    #region unimplemented methods
    public override bool CanSeek
    {
        get { return false; }
    }

    public override bool CanWrite
    {
        get { return true; }
    }

    public override void Flush()
    {
        throw new NotImplementedException();
    }

    public override long Length
    {
        get { throw new NotImplementedException(); }
    }

    public override long Position
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }
    public override long Seek(long offset, SeekOrigin origin)
    {
        throw new NotImplementedException();
    }

    public override void SetLength(long value)
    {
        throw new NotImplementedException();
    }
    #endregion unimplemented methods
}