Getting SerializationException : '<>f__AnonymousType2` is not marked as serializable

Question

i'm getting exception when i call a webmethod in my asp.net application. And i'm sotring my session in Sql Server Db;

<sessionState mode="SQLServer" 
              allowCustomSqlDatabase="true" 
              sqlConnectionString="Password=Shiny365;Data Source=192.168.0.102;Integrated Security=false;Initial Catalog=test;User ID=sa" timeout="1440"/>

here is my code;

[WebMethod]
[ScriptMethod(UseHttpGet = true)]
public static object GetMenusByTabId(int tabId)
{
    var menuManager = new MenuManager();
    List<MenuManager> menus = null;
    AgencyManager user = (AgencyManager)HttpContext.Current.Session["UserCredential"];
    if (user == null)
        return new { status = false };
    menus = menuManager.GetAllMenusByTabId(tabId, user.RoleId);
    HttpContext.Current.Session["MenusWithActivities"] = menus;
    List<MenuManager> parentMenus = menus
                                    .Where(m => m.ParentId == 0)
                                    .ToList<MenuManager>();
    foreach (var parentMenu in parentMenus)
    {
        parentMenu.Children = menus
                                .Select(m => new
                                {
                                    ParentId = m.ParentId,
                                    MenuId = m.MenuId,
                                    Name = m.Name,
                                    Url = m.Url,
                                    Icon = m.Icon,
                                    ActivityView = m.ActivityView
                                })
                                .Where(m => m.ParentId == parentMenu.MenuId && m.ActivityView==true)
                                .ToList<object>();
    }
    return parentMenus.Select(m => new
    {
        MenuId = m.MenuId,
        Name = m.Name,
        Icon = m.Icon,
        Children = m.Children
    });
}

i have marked the MenuManager and AgencyManager as serializable.
When i call this WebMethod, i get the following error;

 Unable to serialize the session state. In 'StateServer' and 'SQLServer' mode, ASP.NET will serialize the session state objects, and as a result non-serializable objects or MarshalByRef objects are not permitted. The same restriction applies if similar serialization is done by the custom session state store in 'Custom' mode.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: Unable to serialize the session state. In 'StateServer' and 'SQLServer' mode, ASP.NET will serialize the session state objects, and as a result non-serializable objects or MarshalByRef objects are not permitted. The same restriction applies if similar serialization is done by the custom session state store in 'Custom' mode.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[SerializationException: Type '<>f__AnonymousType2`6[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Boolean, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' in Assembly 'App_Web_oi13h5hv, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' is not marked as serializable.]
   System.Runtime.Serialization.FormatterServices.InternalGetSerializableMembers(RuntimeType type) +10458455
   System.Runtime.Serialization.FormatterServices.GetSerializableMembers(Type type, StreamingContext context) +230
   System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitMemberInfo() +121
   System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitSerialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder) +178
   System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.Serialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder) +51
   System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Serialize(Object graph, Header[] inHeaders, __BinaryWriter serWriter, Boolean fCheck) +540
   System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph, Header[] headers, Boolean fCheck) +131
   System.Web.Util.AltSerialization.WriteValueToStream(Object value, BinaryWriter writer) +1666

[HttpException (0x80004005): Unable to serialize the session state. In 'StateServer' and 'SQLServer' mode, ASP.NET will serialize the session state objects, and as a result non-serializable objects or MarshalByRef objects are not permitted. The same restriction applies if similar serialization is done by the custom session state store in 'Custom' mode.]
   System.Web.Util.AltSerialization.WriteValueToStream(Object value, BinaryWriter writer) +1754
   System.Web.SessionState.SessionStateItemCollection.WriteValueToStreamWithAssert(Object value, BinaryWriter writer) +34
   System.Web.SessionState.SessionStateItemCollection.Serialize(BinaryWriter writer) +628
   System.Web.SessionState.SessionStateUtility.Serialize(SessionStateStoreData item, Stream stream) +240
   System.Web.SessionState.SessionStateUtility.SerializeStoreData(SessionStateStoreData item, Int32 initialStreamSize, Byte[]& buf, Int32& length, Boolean compressionEnabled) +62
   System.Web.SessionState.SqlSessionStateStore.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData item, Object lockId, Boolean newItem) +135
   System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs) +798
   System.Web.SessionState.SessionStateModule.OnEndRequest(Object source, EventArgs eventArgs) +139
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +136
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69

Answer 1

Anonymous types in C# are not flagged as being serializable. Also, if you send back an annoymous type how would anyone know how to deserialize it, as the type is unknown.

Answer 2

Indeed, anonymous types are not marked [Serializable]. So; if the framework you are using demands serializable objects, you will need to use your own types rather than anonymous ones.

In particular, the two new {...} there, i.e.

return parentMenus.Select(m => new SomeNewMenuTypeYouNeedToCreate
{
    MenuId = m.MenuId,
    Name = m.Name,
    Icon = m.Icon,
    Children = m.Children
});

and:

parentMenu.Children = menus
    .Select(m => new AnotherMenuTypeYouNeedToCreate
    {
        ParentId = m.ParentId,
        MenuId = m.MenuId,
        Name = m.Name,
        Url = m.Url,
        Icon = m.Icon,
        ActivityView = m.ActivityView
    })
    .Where(m => m.ParentId == parentMenu.MenuId && m.ActivityView==true)
    .ToList<object>();

Note: if you just add in the type names, you can get visual studio to create the types and to add all the properties, just by using ctrl+., ⏎. You would then need to add [Serializable] to the two new types.