当实体框架查询Varbinary类型的太大数据时
我试图查询包含文件（1,2 Gb）的varbinary列。
我正在使用实体框架。 见下文：
数据库进行测试
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（任何带有1 Gb的文件）
INSERT INTO [dbo].[BIGDATA]([BIGDATA])
VALUES
((SELECT BulkColumn FROM OPENROWSET(BULK N'C:BigTest.txt', SINGLE_BLOB) AS Document))
控制器下载文件
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;
}
}
我可以通过Select * From BigData在SQL Server上正常查询。
但是，在实体框架（或与ADO命令）我得到这个异常：
为System.OutOfMemoryException
有人知道如何解决这个问题吗？
哇，这是很多数据。 我真的认为你不需要使用EF来获取这些数据，而是使用良好的'ol SqlDataReader。
考虑到.net 4.0的限制，我发现了一个自定义的实现，可以从大量的varbinary列中读取数据。 除了审查代码并确保其中没有.net 4.5快捷方式之外，我无法承认这一点。
http://www.syntaxwarriors.com/2013/stream-varbinary-data-to-and-from-mssql-using-csharp/
Mods - 让我知道是否应该复制/粘贴到答案中，因为原始URL可能不会持久。
编辑：这是来自链接的代码，以防网址消失：
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
}
尝试使用EF“AsNoTracking（）”选项加载数据！
示例：MyContext.MyTable.AsNoTracking（）。其中（x => x .....）
它看起来实体框架不支持将数据流式传输到varbinary字段。
你有几个选择。
编辑：假设你使用.NET 4.5，你应该使用SqlDataReader.GetStream 。 这将允许流式传输文件，而无需将整个内容加载到内存中。
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