哇,那是很多数据。我真的认为你不应该使用 EF 来获取这些数据,而应该使用经典的 SqlDataReader。
考虑到你的 .net 4.0 限制,我找到了一个自定义实现,可以从大型 varbinary 列中流式读取。除了审查代码并确保其中没有 .net 4.5 快捷方式外,我无法为此贡献任何功劳:
http://www.syntaxwarriors.com/2013/stream-varbinary-data-to-and-from-mssql-using-csharp/
Mods - 让我知道这样的东西是否应该复制/粘贴到答案中,因为原始URL可能不会持久存在。
编辑:
如果URL消失了,这里是链接中的代码:
用法:
VarbinaryStream filestream = new VarbinaryStream(
DbContext.Database.Connection.ConnectionString,
"FileContents",
"Content",
"ID",
(int)filepost.ID,
true);
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)
{
_Connection = new SqlConnection(ConnectionString);
_TableName = TableName;
_BinaryColumn = BinaryColumn;
_KeyColumn = KeyColumn;
_KeyValue = KeyValue;
_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)
{
}
}
}
public override void Write(byte[] buffer, int index, int count)
{
try
{
if (_Connection.State != ConnectionState.Open)
_Connection.Open();
if (_Offset == 0)
{
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
{
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)
{
}
}
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)
{
}
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
}