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How to: Sample Session-State Store Provider 

Demonstrates a session-state store provider implementation.

The following code example program shows how to implement a session-state store provider. For details about how to build this provider and use it in an ASP.NET application, see Sample Session-State Store Provider.

Example

using System;
using System.Web;
using System.Web.Configuration;
using System.Configuration;
using System.Configuration.Provider;
using System.Collections.Specialized;
using System.Web.SessionState;
using System.Data;
using System.Data.Odbc;
using System.Diagnostics;
using System.IO;


/*
This session state store provider supports the following schema:

  CREATE TABLE Sessions
  (
    SessionId       Text(80)  NOT NULL,
    ApplicationName Text(255) NOT NULL,
    Created         DateTime  NOT NULL,
    Expires         DateTime  NOT NULL,
    LockDate        DateTime  NOT NULL,
    LockId          Integer   NOT NULL,
    Timeout         Integer   NOT NULL,
    Locked          YesNo     NOT NULL,
    SessionItems    Memo,
    Flags           Integer   NOT NULL,
      CONSTRAINT PKSessions PRIMARY KEY (SessionId, ApplicationName)
  )

This session state store provider does not automatically clean up 
expired session item data. It is recommended
that you periodically delete expired session information from the
data store with the following code (where 'conn' is the OdbcConnection
for the session state store provider):

  string commandString = "DELETE FROM Sessions WHERE Expires < ?";
  OdbcConnection conn = new OdbcConnection(connectionString);
  OdbcCommand cmd = new OdbcCommand(commandString, conn);
  cmd.Parameters.Add("@Expires", OdbcType.DateTime).Value = DateTime.Now;
  conn.Open();
  cmd.ExecuteNonQuery();
  conn.Close();
  
*/

namespace Samples.AspNet.Session
{

  public sealed class OdbcSessionStateStore : SessionStateStoreProviderBase
  {
    private SessionStateSection pConfig = null;
    private string connectionString;
    private ConnectionStringSettings pConnectionStringSettings;
    private string eventSource = "OdbcSessionStateStore";
    private string eventLog = "Application";
    private string exceptionMessage = 
      "An exception occurred. Please contact your administrator.";
    private string pApplicationName;


    //
    // If false, exceptions are thrown to the caller. If true,
    // exceptions are written to the event log.
    //

    private bool pWriteExceptionsToEventLog = false;

    public bool WriteExceptionsToEventLog
    {
      get { return pWriteExceptionsToEventLog; }
      set { pWriteExceptionsToEventLog = value; }
    }


    //
    // The ApplicationName property is used to differentiate sessions
    // in the data source by application.
    //

    public string ApplicationName
    {
      get { return pApplicationName; }
    }


    public override void Initialize(string name, NameValueCollection config)
    {
      //
      // Initialize values from web.config.
      //

      if (config == null)
        throw new ArgumentNullException("config");

      if (name == null || name.Length == 0)
        name = "OdbcSessionStateStore";

      if (String.IsNullOrEmpty(config["description"]))
      {
        config.Remove("description");
        config.Add("description", "Sample ODBC Session State Store provider");
      }

      // Initialize the abstract base class.
      base.Initialize(name, config);


      //
      // Initialize the ApplicationName property.
      //

      pApplicationName = 
        System.Web.Hosting.HostingEnvironment.ApplicationVirtualPath;


      //
      // Get <sessionState> configuration element.
      //

      Configuration cfg =
        WebConfigurationManager.OpenWebConfiguration(ApplicationName);
      pConfig = 
        (SessionStateSection)cfg.GetSection("system.web/sessionState");

      
      //
      // Initialize connection string.
      //

      pConnectionStringSettings = 
        ConfigurationManager.ConnectionStrings[config["connectionStringName"]];

      if (pConnectionStringSettings == null || 
        pConnectionStringSettings.ConnectionString.Trim() == "")
      {
        throw new ProviderException("Connection string cannot be blank.");
      }

      connectionString = pConnectionStringSettings.ConnectionString;


      //
      // Initialize WriteExceptionsToEventLog
      //

      pWriteExceptionsToEventLog = false;

      if (config["writeExceptionsToEventLog"] != null)
      {
        if (config["writeExceptionsToEventLog"].ToUpper() == "TRUE") 
          pWriteExceptionsToEventLog = true;
      }
    }


    //
    // SessionStateStoreProviderBase members
    //

    public override void Dispose()
    {
    }


    //
    // SessionStateProviderBase.SetItemExpireCallback
    //

    public override bool SetItemExpireCallback(SessionStateItemExpireCallback expireCallback)
    {
      return false;
    }


    //
    // SessionStateProviderBase.SetAndReleaseItemExclusive
    //

    public override void SetAndReleaseItemExclusive(HttpContext context,
      string id,
      SessionStateStoreData item,
      object lockId,
      bool newItem)                                           
    {
      // Serialize the SessionStateItemCollection as a string.
      string sessItems = Serialize((SessionStateItemCollection)item.Items);

      OdbcConnection conn = new OdbcConnection(connectionString);
      OdbcCommand cmd;
      OdbcCommand deleteCmd = null;

      if (newItem)
      {
        // OdbcCommand to clear an existing expired session if it exists.
        deleteCmd = new OdbcCommand("DELETE FROM Sessions " +
            "WHERE SessionId = ? AND ApplicationName = ? AND Expires < ?", conn);
        deleteCmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
        deleteCmd.Parameters.Add
          ("@ApplicationName", OdbcType.VarChar, 255).Value = ApplicationName;
        deleteCmd.Parameters.Add
          ("@Expires", OdbcType.DateTime).Value = DateTime.Now;

        // OdbcCommand to insert the new session item.
        cmd = new OdbcCommand("INSERT INTO Sessions " +
          " (SessionId, ApplicationName, Created, Expires, " +
          "  LockDate, LockId, Timeout, Locked, SessionItems, Flags) " +
          " Values(?, ?, ?, ?, ?, ? , ?, ?, ?, ?)", conn);
        cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
        cmd.Parameters.Add
          ("@ApplicationName", OdbcType.VarChar, 255).Value = ApplicationName;
        cmd.Parameters.Add
          ("@Created", OdbcType.DateTime).Value = DateTime.Now;
        cmd.Parameters.Add
          ("@Expires", OdbcType.DateTime).Value = DateTime.Now.AddMinutes((Double)item.Timeout);
        cmd.Parameters.Add
          ("@LockDate", OdbcType.DateTime).Value = DateTime.Now;
        cmd.Parameters.Add("@LockId", OdbcType.Int).Value = 0;
        cmd.Parameters.Add
          ("@Timeout", OdbcType.Int).Value = item.Timeout;
        cmd.Parameters.Add("@Locked", OdbcType.Bit).Value = false;
        cmd.Parameters.Add
          ("@SessionItems", OdbcType.VarChar, sessItems.Length).Value = sessItems;
        cmd.Parameters.Add("@Flags", OdbcType.Int).Value = 0;
      }
      else
      {
        // OdbcCommand to update the existing session item.
        cmd = new OdbcCommand(
          "UPDATE Sessions SET Expires = ?, SessionItems = ?, Locked = ? " +
          " WHERE SessionId = ? AND ApplicationName = ? AND LockId = ?", conn);
        cmd.Parameters.Add("@Expires", OdbcType.DateTime).Value = 
          DateTime.Now.AddMinutes((Double)item.Timeout);
        cmd.Parameters.Add("@SessionItems", 
          OdbcType.VarChar, sessItems.Length).Value = sessItems;
        cmd.Parameters.Add("@Locked", OdbcType.Bit).Value = false;
        cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
        cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
          255).Value = ApplicationName;
        cmd.Parameters.Add("@LockId", OdbcType.Int).Value = lockId;
      }

      try
      {
        conn.Open();

        if (deleteCmd != null)
          deleteCmd.ExecuteNonQuery();

        cmd.ExecuteNonQuery();
      }
      catch (OdbcException e)
      {
        if (WriteExceptionsToEventLog)
        {
          WriteToEventLog(e, "SetAndReleaseItemExclusive");
          throw new ProviderException(exceptionMessage);
        }
        else
          throw e;
      }
      finally
      {
        conn.Close();
      }
    }


    //
    // SessionStateProviderBase.GetItem
    //

    public override SessionStateStoreData GetItem(HttpContext context,
      string id,
      out bool locked,
      out TimeSpan lockAge,
      out object lockId,
      out SessionStateActions actionFlags)
    {
      return GetSessionStoreItem(false, context, id, out locked,
        out lockAge, out lockId, out actionFlags);
    }


    //
    // SessionStateProviderBase.GetItemExclusive
    //

    public override SessionStateStoreData GetItemExclusive(HttpContext context, 
      string id,
      out bool locked,
      out TimeSpan lockAge,
      out object lockId,
      out SessionStateActions actionFlags)
    {
      return GetSessionStoreItem(true, context, id, out locked, 
        out lockAge, out lockId, out actionFlags);
    }


    //
    // GetSessionStoreItem is called by both the GetItem and 
    // GetItemExclusive methods. GetSessionStoreItem retrieves the 
    // session data from the data source. If the lockRecord parameter
    // is true (in the case of GetItemExclusive), then GetSessionStoreItem
    // locks the record and sets a new LockId and LockDate.
    //

    private SessionStateStoreData GetSessionStoreItem(bool lockRecord,
      HttpContext context, 
      string id,
      out bool locked,
      out TimeSpan lockAge,
      out object lockId,
      out SessionStateActions actionFlags)
    {
      // Initial values for return value and out parameters.
      SessionStateStoreData item = null;
      lockAge = TimeSpan.Zero;
      lockId = null;
      locked = false;
      actionFlags = 0;

      // ODBC database connection.
      OdbcConnection conn = new OdbcConnection(connectionString);
      // OdbcCommand for database commands.
      OdbcCommand cmd = null;              
      // DataReader to read database record.
      OdbcDataReader reader = null;  
      // DateTime to check if current session item is expired.
      DateTime expires;              
      // String to hold serialized SessionStateItemCollection.
      string serializedItems = "";
      // True if a record is found in the database.
       bool foundRecord = false;    
      // True if the returned session item is expired and needs to be deleted.
       bool deleteData = false;             
      // Timeout value from the data store.
      int timeout = 0;               

      try
      {
        conn.Open();

        // lockRecord is true when called from GetItemExclusive and
        // false when called from GetItem.
        // Obtain a lock if possible. Ignore the record if it is expired.
        if (lockRecord)
        {
          cmd = new OdbcCommand(
            "UPDATE Sessions SET" +
            " Locked = ?, LockDate = ? " +
            " WHERE SessionId = ? AND ApplicationName = ? AND Locked = ? AND Expires > ?", conn);
          cmd.Parameters.Add("@Locked", OdbcType.Bit).Value = true;
          cmd.Parameters.Add("@LockDate", OdbcType.DateTime).Value 
            = DateTime.Now;
          cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
          cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
            255).Value = ApplicationName;
          cmd.Parameters.Add("@Locked", OdbcType.Int).Value = false;
          cmd.Parameters.Add
            ("@Expires", OdbcType.DateTime).Value = DateTime.Now;

          if (cmd.ExecuteNonQuery() == 0)
            // No record was updated because the record was locked or not found.
            locked = true;             
          else
            // The record was updated.

            locked = false;
          }

        // Retrieve the current session item information.
        cmd = new OdbcCommand(
          "SELECT Expires, SessionItems, LockId, LockDate, Flags, Timeout " +
          "  FROM Sessions " +
          "  WHERE SessionId = ? AND ApplicationName = ?", conn);
        cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
        cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
          255).Value = ApplicationName;

        // Retrieve session item data from the data source.
        reader = cmd.ExecuteReader(CommandBehavior.SingleRow);
        while (reader.Read())
        {
          expires = reader.GetDateTime(0);

          if (expires < DateTime.Now)
          {
            // The record was expired. Mark it as not locked.
            locked = false;     
            // The session was expired. Mark the data for deletion.
            deleteData = true;
            }
          else
            foundRecord = true;

          serializedItems = reader.GetString(1);
          lockId = reader.GetInt32(2);
          lockAge = DateTime.Now.Subtract(reader.GetDateTime(3));
          actionFlags = (SessionStateActions)reader.GetInt32(4);
          timeout = reader.GetInt32(5);
        }
        reader.Close();


        // If the returned session item is expired, 
        // delete the record from the data source.
        if (deleteData)   
        {
          cmd = new OdbcCommand("DELETE FROM Sessions " +
            "WHERE SessionId = ? AND ApplicationName = ?", conn);
          cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
          cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
            255).Value = ApplicationName;

          cmd.ExecuteNonQuery();
        }

        // The record was not found. Ensure that locked is false.
        if (!foundRecord)
          locked = false;
        
        // If the record was found and you obtained a lock, then set 
        // the lockId, clear the actionFlags,
        // and create the SessionStateStoreItem to return.
        if (foundRecord && !locked)
        {
          lockId = (int)lockId + 1;

          cmd = new OdbcCommand("UPDATE Sessions SET" +
            " LockId = ?, Flags = 0 " +
            " WHERE SessionId = ? AND ApplicationName = ?", conn);
          cmd.Parameters.Add("@LockId", OdbcType.Int).Value = lockId;
          cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
          cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 255).Value = ApplicationName;

          cmd.ExecuteNonQuery();

          // If the actionFlags parameter is not InitializeItem, 
          // deserialize the stored SessionStateItemCollection.
          if (actionFlags == SessionStateActions.InitializeItem)
            item = CreateNewStoreData(context, pConfig.Timeout.Minutes);
          else
            item = Deserialize(context, serializedItems, timeout);
        }
      }
      catch (OdbcException e)
      {
        if (WriteExceptionsToEventLog)
        {
          WriteToEventLog(e, "GetSessionStoreItem");
          throw new ProviderException(exceptionMessage);
        }
        else
          throw e;
      }
      finally
      {
        if (reader != null) { reader.Close(); }
        conn.Close();
      } 

      return item;
    }




    //
    // Serialize is called by the SetAndReleaseItemExclusive method to 
    // convert the SessionStateItemCollection into a Base64 string to    
    // be stored in an Access Memo field.
    //

    private string Serialize(SessionStateItemCollection items)
    {
      MemoryStream ms = new MemoryStream();
      BinaryWriter writer = new BinaryWriter(ms);

      if (items != null)
        items.Serialize(writer);

      writer.Close();

      return Convert.ToBase64String(ms.ToArray());
    }

    //
    // DeSerialize is called by the GetSessionStoreItem method to 
    // convert the Base64 string stored in the Access Memo field to a 
    // SessionStateItemCollection.
    //

    private SessionStateStoreData Deserialize(HttpContext context, 
      string serializedItems, int timeout)
    {
      MemoryStream ms = 
        new MemoryStream(Convert.FromBase64String(serializedItems));

      SessionStateItemCollection sessionItems =
        new SessionStateItemCollection();

      if (ms.Length > 0)
      {
          BinaryReader reader = new BinaryReader(ms);
          sessionItems = SessionStateItemCollection.Deserialize(reader);
      }

      return new SessionStateStoreData(sessionItems,
        SessionStateUtility.GetSessionStaticObjects(context),
        timeout);
    }

    //
    // SessionStateProviderBase.ReleaseItemExclusive
    //

    public override void ReleaseItemExclusive(HttpContext context,
      string id,
      object lockId)
    {
      OdbcConnection conn = new OdbcConnection(connectionString);
      OdbcCommand cmd = 
        new OdbcCommand("UPDATE Sessions SET Locked = 0, Expires = ? " +
        "WHERE SessionId = ? AND ApplicationName = ? AND LockId = ?", conn);
      cmd.Parameters.Add("@Expires", OdbcType.DateTime).Value = 
        DateTime.Now.AddMinutes(pConfig.Timeout.Minutes);
      cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
      cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
        255).Value = ApplicationName;
      cmd.Parameters.Add("@LockId", OdbcType.Int).Value = lockId;

      try
      {
        conn.Open();

        cmd.ExecuteNonQuery();
      }
      catch (OdbcException e)
      {
        if (WriteExceptionsToEventLog)
        {
          WriteToEventLog(e, "ReleaseItemExclusive");
          throw new ProviderException(exceptionMessage);
        }
        else
          throw e;
      }
      finally
      {
        conn.Close();
      }      
    }


    //
    // SessionStateProviderBase.RemoveItem
    //

    public override void RemoveItem(HttpContext context,
      string id,
      object lockId,
      SessionStateStoreData item)
    {
      OdbcConnection conn = new OdbcConnection(connectionString);
      OdbcCommand cmd = new OdbcCommand("DELETE * FROM Sessions " +
        "WHERE SessionId = ? AND ApplicationName = ? AND LockId = ?", conn);
      cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
      cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
        255).Value = ApplicationName;
      cmd.Parameters.Add("@LockId", OdbcType.Int).Value = lockId;

      try
      {
        conn.Open();

        cmd.ExecuteNonQuery();
      }
      catch (OdbcException e)
      {
        if (WriteExceptionsToEventLog)
        {
          WriteToEventLog(e, "RemoveItem");
          throw new ProviderException(exceptionMessage);
        }
        else
          throw e;
      }
      finally
      {
        conn.Close();
      } 
    }



    //
    // SessionStateProviderBase.CreateUninitializedItem
    //

    public override void CreateUninitializedItem(HttpContext context,
      string id,
      int timeout)
    {
       OdbcConnection conn = new OdbcConnection(connectionString);
       OdbcCommand cmd = new OdbcCommand("INSERT INTO Sessions " +
         " (SessionId, ApplicationName, Created, Expires, " +
         "  LockDate, LockId, Timeout, Locked, SessionItems, Flags) " +
         " Values(?, ?, ?, ?, ?, ? , ?, ?, ?, ?)", conn);
      cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
      cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
        255).Value = ApplicationName;
      cmd.Parameters.Add("@Created", OdbcType.DateTime).Value 
        = DateTime.Now;
      cmd.Parameters.Add("@Expires", OdbcType.DateTime).Value 
        = DateTime.Now.AddMinutes((Double)timeout);
      cmd.Parameters.Add("@LockDate", OdbcType.DateTime).Value 
        = DateTime.Now;
      cmd.Parameters.Add("@LockId", OdbcType.Int).Value = 0;
      cmd.Parameters.Add("@Timeout", OdbcType.Int).Value = timeout;
      cmd.Parameters.Add("@Locked", OdbcType.Bit).Value = false;
      cmd.Parameters.Add("@SessionItems", OdbcType.VarChar, 0).Value = "";
      cmd.Parameters.Add("@Flags", OdbcType.Int).Value = 1;

      try
      {
        conn.Open();

        cmd.ExecuteNonQuery();
      }
      catch (OdbcException e)
      {
        if (WriteExceptionsToEventLog)
        {
          WriteToEventLog(e, "CreateUninitializedItem");
          throw new ProviderException(exceptionMessage);
        }
        else
          throw e;
      }
      finally
      {
        conn.Close();
      }
    }


    //
    // SessionStateProviderBase.CreateNewStoreData
    //

    public override SessionStateStoreData CreateNewStoreData(
      HttpContext context,
      int timeout)
    {
      return new SessionStateStoreData(new SessionStateItemCollection(),
        SessionStateUtility.GetSessionStaticObjects(context),
        timeout);
    }



    //
    // SessionStateProviderBase.ResetItemTimeout
    //

    public override void ResetItemTimeout(HttpContext context,
                                          string id)
    {
      OdbcConnection conn = new OdbcConnection(connectionString);
      OdbcCommand cmd = 
        new OdbcCommand("UPDATE Sessions SET Expires = ? " +
        "WHERE SessionId = ? AND ApplicationName = ?", conn);
      cmd.Parameters.Add("@Expires", OdbcType.DateTime).Value 
        = DateTime.Now.AddMinutes(pConfig.Timeout.Minutes);
      cmd.Parameters.Add("@SessionId", OdbcType.VarChar, 80).Value = id;
      cmd.Parameters.Add("@ApplicationName", OdbcType.VarChar, 
        255).Value = ApplicationName;

      try
      {
        conn.Open();

        cmd.ExecuteNonQuery();
      }
      catch (OdbcException e)
      {
        if (WriteExceptionsToEventLog)
        {
          WriteToEventLog(e, "ResetItemTimeout");
          throw new ProviderException(exceptionMessage);
        }
        else
          throw e;
      }
      finally
      {
        conn.Close();
      }
    }


    //
    // SessionStateProviderBase.InitializeRequest
    //

    public override void InitializeRequest(HttpContext context)
    {
    }


    //
    // SessionStateProviderBase.EndRequest
    //

    public override void EndRequest(HttpContext context)
    {
    }


    //
    // WriteToEventLog
    // This is a helper function that writes exception detail to the 
    // event log. Exceptions are written to the event log as a security
    // measure to ensure private database details are not returned to 
    // browser. If a method does not return a status or Boolean
    // indicating the action succeeded or failed, the caller also 
    // throws a generic exception.
    //

    private void WriteToEventLog(Exception e, string action)
    {
      EventLog log = new EventLog();
      log.Source = eventSource;
      log.Log = eventLog;

      string message = 
        "An exception occurred communicating with the data source.\n\n";
      message += "Action: " + action + "\n\n";
      message += "Exception: " + e.ToString();

      log.WriteEntry(message);
    }
  }
}

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