Question

Say, we have a table with some large text field containg jpg-files’ binary data. The task is to get those files from a database on disk. So, at first I decided to do the following:

MyDataContext dc = new MyDataContext();
foreach(ImageTable t in dc.ImageTable.OrderBy(i=>i.Id))
{
    using (StreamWriter writer = new StreamWriter(new FileStream(string.Concat(t.Name,".jpg"), FileMode.CreateNew), Encoding.GetEncoding(1251)))
    {
          writer.Write(t.Data);
          writer.Close();
    }
}

But as soon as the table had about 20 thousand of rows, in a while I got an OutOfMemoryException.

In the end, to avoid loading of all the rows into one datacontext I did the following:

MyDataContext dc = new MyDataContext();
foreach(int id in dc.ImageTable.OrderBy(i=>i.Id).Select(i=>i.Id))
{
     using (MyDataContext _dc = new MyDataContext())
     {
           ImageTable t = _dc.ImageTable.FirstOrDefault(i => i.Id == id);
           using (StreamWriter writer = new StreamWriter(new FileStream(string.Concat(t.Name,".jpg"), FileMode.CreateNew), Encoding.GetEncoding(1251)))
           {
                writer.Write(t.Data);
                writer.Close();
           }
      }
}    

So each row is loaded by a separate datacontext…no memory problem left!
But surely it’s not the best approach to do the task.

Could anyone suggest something?

Answer 1

You could try switching off object tracking:

_dc.ObjectTrackingEnabled = false;