Storing LINQ Objects in SQL-Based Session State

// January 30th, 2008 // LINQ

Scott Hanselman recently posted about various options you have for session storage while using ASP.Net. In the comments of his post I brough up an issue I recently encountered at work (where we use SQL Server session state):

LINQ-To-Sql generated objects are not marked [Serializable] and cannot be stored in out-of-process session storage.

To get around this I have whipped up the following helper class which will serialize LINQ-To-Sql objects if you set the DataContext's Serializable property to "Unidirectional".

Note: The following class does not current work for storing List<X> where X is a LINQ-To-Sql object. I'll be working to resolve that sometime later this week. 

   1: using System;

   2: using System.IO;

   3: using System.Runtime.Serialization;

   4: using System.Text;

   5: using System.Xml;

   6: using System.Web;

   7: 

   8: namespace SquaredRoot.Helper

   9: {

  10:   public class SessionHelper

  11:   {

  12: 

  13:     private SessionHelper(){}

  14: 

  15:         public static T Get<T>( string key ) where T : class

  16:         {

  17: 

  18:             object o = HttpContext.Current.Session[key];

  19:             if( o == null )

  20:                 return default( T );

  21: 

  22:             if( o.GetType() == typeof( string ) && typeof( T ) != typeof( string ) )

  23:             {

  24:                 string s = o as string;

  25:                 Stream stream = new MemoryStream( Encoding.Unicode.GetBytes(s) );

  26:                 XmlDictionaryReader xml = XmlDictionaryReader.CreateTextReader( stream, new XmlDictionaryReaderQuotas() );

  27:                 DataContractSerializer dcs = new DataContractSerializer( typeof( T ) );

  28:                 T t = (T)dcs.ReadObject( xml, true );

  29:                 xml.Close();

  30:                 return t;

  31:             }

  32:             else

  33:                 return o as T;

  34: 

  35:         }

  36: 

  37:         private static bool HasClassAttribute( object o, Type attribute, bool inherit )

  38:         {

  39:             return ( o.GetType().GetCustomAttributes( attribute, inherit ).Length > 0 );

  40:         }

  41: 

  42:         public static void Set( string key, object item )

  43:         {

  44: 

  45:             object value = item;

  46:             if( HasClassAttribute( item, typeof(DataContractAttribute), false )

  47:         && !HasClassAttribute( item, typeof(SerializableAttribute), false ) )

  48:             {

  49:                 DataContractSerializer dcs = new DataContractSerializer(item.GetType());

  50:                 StringBuilder sb = new StringBuilder();

  51:                 XmlWriter writer = XmlWriter.Create(sb);

  52:                 dcs.WriteObject( writer, item );

  53:                 writer.Close();

  54:                 value = sb.ToString();

  55:             }

  56: 

  57:             if( HttpContext.Current.Session[key] == null )

  58:         HttpContext.Current.Session.Add( key, value );

  59:             else

  60:         HttpContext.Current.Session[key] = value;

  61: 

  62:         }

  63: 

  64:     }

  65: }
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3 Responses to “Storing LINQ Objects in SQL-Based Session State”

  1. Nicholas says:
    April 23, 2008 at 3:49 pm

    Did you ever get the .ToList() version working?

    This issue is so frustrating..

  2. Kevin Read says:
    July 31, 2008 at 5:56 pm

    To get the .ToList() version working, all I did was to remove the check for the DataContractAttribute on the item. (Line 46 on the code example above.)

  3. Patrick says:
    February 26, 2009 at 3:59 pm

    Hi you mean for List() version, I just change line 46 to

    if(!HasClassAttribute( item, typeof(SerializableAttribute), false ) )