May 26, 2008

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I am preparing the next IT Boxing event: Platforms for Enterprise Development, Web Services and SOA. The event will be held on 25 June 2008 from 17:30 in Park Hotel Moscow in Sofia.

Platforms for Enterprise Development, Web Services and SOA

Enterprise applications are complex distributed software systems designed to meet the requirements and needs of large organizations. Typically enterprise systems are running inside enterprise platforms such as Java EE and Microsoft .NET and drive the entire business processes within the organizations.

Service-oriented architecture (SOA) provides a relatively new approach to building enterprise applications based on the concept of developing, publishing and consuming loosely coupled software components called “services”.

Web services and their complete protocol stack (HTTP / SOAP / WSDL) provide standards based infrastructure for building SOA solutions that is supported by virtually any enterprise platform.

Large industry vendors like IBM, Oracle, Microsoft and SAP provide platforms for enterprise applications supporting solid infrastructure for building, deploying, running and managing large multitier and SOA applications.

In this issue of the IT Boxing Championship the fans of the worlds leading Java EE and Microsoft .NET platforms will dispute which platform is better.

Venue

The event will be held on 25 June 2008, starting from 18:00 h in Park-hotel Moscow, Sofia, hall Moscow. The hall capacity is 350 people.

Agenda

Java Enterprise Edition (Java EE) and its Web Services and SOA Stack

Java Platform, Enterprise Edition (Java EE) is a widely used platform for server side development in the Java programming language. Java EE and is an industry standard for implementing enterprise-class distributed systems and service-oriented architecture (SOA) applications. It provides solid architecture and programming model for development and execution of Web applications, Web services, distributed applications, components, services and SOA solutions.

Java EE is designed for enterprise systems and natively supports the latest Web services standards (W3C and OASIS) and provides solid infrastructure for SOA applications.

Java EE applications run in an application server such as JBoss, IBM WebSphere, SAP Netweaver and Oracle Containers for Java EE, which implement the Java EE specification and provide many additional services.

Microsoft .NET Platform and its Web Services and SOA Stack

Microsoft .NET is a leading industry platform for developing enterprise Web applications, Web services and SOA solutions. Its heart, the .NET Framework provides a stable infrastructure, programming model and execution environment for developing and running applications on Windows servers, clients, and mobile or embedded devices.

.NET Framework with its Windows Communication Foundation (WCF) and Windows Workflow Foundation (WF) provides a built-in infrastructure of technologies for building connected systems and workflow enabled applications on Windows. It implements the most recent Web services standards and provides easy-to-use SOA environment.

Free Event

The event is free and the hall is large, so please come with your friends! Everyone will get small gifts from our sponsors.

Tags: enterprise, enterprise platforms, hotel moscow, Microsoft, NET, protocol stack, service oriented architecture, service oriented architecture soa, SOA, Technical

May 16, 2008

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In this article I will focus on buiding the data access layer in ASP.NET 3.5 Web applications with LINQ to SQL and SQL Server.

Lots of articles introduce the LINQ technology, the LINQ to SQL object-relational mapping technology and ASP.NET 3.5 so I will skips these introduction and will explain the main problem I found when I started using LINQ to SQL in ASP.NET web applications. The problem was standard: “How to manage the database session?”.

Managing LINQ to SQL Database Session (the DataContext) in ASP.NET Web Applications

As an experienced Java developer when I started using LINQ to SQL with ASP.NET I had rich experience with Hibernate, NHibernate and other object-relational mapping (ORM) engines like OpenJPA. I was familiar with the common patterns and approaches used to manage the database session and transaction in Web applications (mostly in Java) and I wanted to leverage my existing experience.

The “Session-per-Request” Pattern

The first idea I came upon was to implement the classical “session-per-request” pattern. This pattern opens the database sesion in the beginning of the HTTP request and closes it at the end of the HTTP request. Thus the dynamic Web pages that interract with the database assume the connection is already open. Usually I also start a transaction along with the session and commit it when closing the session. If I need multiple transactions, I start and end them manually. In the most common case the developer do not write any additional code to handle the database connection and session. This worksvery wells for lots of my projects.

The “Session-per-Request” Pattern in Java (with Servlet Filter)

In Java the “session-per-request” pattern is best implemented with so called “servlet filter” which is just an HTTP request interceptior. Inside the intercepted HTTP request I open the Hibernate session, process the HTTP request and finally close the HTTP session. I can go further and catch the exceptions and rollback transaction as well. Typically after opening the session I put it in the current thread’s local context so all my database access objects (DAO classes) do not need to take it as a parameter. The DAO objects just get the session from the local context of the currently running thread. This works great in Java for many projects and many years.

Typical Java code for this can look like the following:

public class SessionPerRequestFilter implements Filter {
  public void doFilter(ServletRequest request, ServletResponse response,
  FilterChain chain) throws IOException, ServletException {
    try {
      HibernateSessionManager.openSession();
      chain.doFilter(request, response);
    } finally {
      HibernateSessionManager.closeSession();
    }
  }
  public void init(FilterConfig config) throws ServletException { }
  public void destroy() { }
}

In the above code the openSession() and closeSession() handle the transaction as well.

The “Session-per-Request” Pattern in ASP.NET

I wanted to implement the same pattern in ASP.NET with LINQ to SQL. In ASP.NET we don’t have servlet filters and HTTP request interception functionality. We have something similar, but with limited functionality and flexibility, the so called HTTP handlers. In ASP.NET the HTTP handlers can catch specific events that are produced during the execution lifecycle of the ASP.NET pages. We can catch events like BeginRequest and EndRequest but we can’t completely override the request processing logic (we don’t have chain.doFilter(request, response) which can be called or not).

In HTTP Module BeginRequest and EndRequest Execute in Different Threads

I don’t know if this is an optimization of architectural issue, but unlike in Java EE in ASP.NET the events BeginRequest and EndRequest for the same HTTP request can execute in different threads. ASP.NET actually uses the same thread for executing several concurrent requests. Really! Thus we cannot open the database connection in BeginRequest, put it in the thread’s local context, use it from the DAO classes when rendering the application’s dynamic web pages and finally in EndRequest remove it from the thread’s local context. No, this does not work with HttpHandler. I found this by debugging.

I tried to fix this by using the Application_BeginRequest and Application_EndRequest in Global.asax, but the result was the same: sometimes ASP.NET runs Application_BeginRequest and Application_EndRequest event handlers belonging to concurrent requests in the same thread.

After lost of experiments I fixed this.

In Global.asax Application_PreRequestHandlerExecute and Application_PostRequestHandlerExecutein Execute in the Same Thread

Following the documentation for the ASP.NET execution lifecycle I found that I can intercept the execution of the HTTP requests in many other ways, in the different stages of the request procesing. I found that the events Application_PreRequestHandlerExecute and Application_PostRequestHandlerExecute are called in the same thread for each request. If we have two concurrent HTTP requests, ASP.NET wil run two parallel threads and will execute each request in separate thread. The same applies for the Application_PreRequestHandlerExecute and Application_PostRequestHandlerExecute events.

Implementing Session-Per-Request Pattern in ASP.NET with LINQ to SQL

Finally I put the following code in Global.asax:

void Application_PreRequestHandlerExecute(object sender, EventArgs e)
{
  DataContextManager.CreateMMDataContext();
}

void Application_PostRequestHandlerExecute(object sender, EventArgs e)
{
  DataContextManager.DisposeMMDataContext();
}

This is what I have in the DataContextManager class which handles my DataContext (database session) by few static methods:

</pre>
public class DataContextManager
{
 private static LocalDataStoreSlot dataContextSlot = Thread.GetNamedDataSlot("DataContext");

/// <summary></summary>
 /// Creates new data context and stores it in the current thread's context.
 /// If data context already exists, do nothing.
 ///
 public static void CreateMMDataContext()
 {
 MMDataContext mmDataContext = (MMDataContext)Thread.GetData(dataContextSlot);
 if (mmDataContext == null)
 {
 mmDataContext = new MMDataContext();
 Thread.SetData(dataContextSlot, mmDataContext);
 }
 }

/// <summary></summary>
 /// Return the data context associated with the current thread.
 /// Throws and InvalidOperationException if no data context is associated with the current thread.
 ///
 public static MMDataContext MMDataContext
 {
 get
 {
 MMDataContext mmDataContext = (MMDataContext)Thread.GetData(dataContextSlot);
 if (mmDataContext != null)
 {
 return mmDataContext;
 }
 else
 {
 throw new InvalidOperationException(
 "The data context is not found in the current thread's context.");
 }
 }
 }

/// <summary></summary>
 /// Disposes the data context currently associated with the current thread
 /// and removes it from the thread context. If no data context is asssociated
 /// with the current thread, does nothing.
 ///
 public static void DisposeMMDataContext()
 {
 MMDataContext mmDataContext = (MMDataContext)Thread.GetData(dataContextSlot);
 if (mmDataContext != null)
{
 mmDataContext.Dispose();
 Thread.SetData(dataContextSlot, null);
 }
 }
}

In the examples my data context (.dbml mapping file) is called MMDataContext.

Implementing the Data Access Logic (DAO Classes)

Finally I implemented the data access logic as set of DAO classes and a generic basic DAO parent class:

</pre>
public class GenericDAO<tentity></tentity> where TEntity : class
{
protected static MMDataContext MMDataContext
{
get
{
return DataContextManager.MMDataContext;
}
}

public static List<tentity></tentity> FindAll()
{
List<tentity></tentity> enitities = MMDataContext.GetTable<tentity></tentity>().ToList<tentity></tentity>();
return enitities;
}

public static void SubmitChanges()
{
MMDataContext.SubmitChanges();
}
}

I wanted to implement the method:

public static T FindByPrimaryKey(int countryId)

… but I failed. I think there is no way to do this as generic. This is a weakness of the LINQ to SQL framework.

Once I have the generic baseic DAO class I can use it to define my DAP classes, e.g.

public class EventLogDAO : GenericDAO<eventlog></eventlog>
{
public static EventLog[] GetAllLogs(string userEmail)
{
var logs = from l in MMDataContext.EventLogs
where l.User.Email == userEmail
orderby l.EventDate descending
select l;
List<eventlog></eventlog> results = new List<eventlog></eventlog>();
if (logs.Count() != 0)
{
results = logs.ToList();
}
return results.ToArray();
}

public static EventLog FindById(int id)
{
EventLog log = (from l in MMDataContext.EventLogs
where l.EventLogId == id
select l).SingleOrDefault();
return log;
}

public static void MarkAsRead(int id)
{
EventLog log = FindById(id);
log.MessageRead = true;
MMDataContext.SubmitChanges();
}
...
}

Implementing the ASPX Pages that Use the DAO Classes

Once I have implemented the DAO classes I can use them directly in an .aspx page or ascx user control by ObjectDataSource or at event handler. All methods are static and developers do not need to care about thesession management. A sample ASPX page is given below:

< %@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true"
    CodeFile="BrowseCities.aspx.cs" Inherits="BrowseCities" Title="All Cities" %>
<asp :Content ID="ContentBrowseCities" ContentPlaceHolderID="ContentPlaceHolderBody"
    runat="Server">
    <div style="text-align: center">
        <asp :ListView ID="ListViewCities" runat="server" ItemPlaceholderID="PlaceHolderCity"
            DataSourceID="ObjectDataSourceCities">
            <layouttemplate>
                <asp  laceHolder ID="PlaceHolderCity" runat="server" />
            </layouttemplate>
            <itemtemplate>
                <asp :LinkButton ID="LinkButtonCity" runat="server" OnCommand="LinkButtonCity_Click"
                Text="<%# Container.DataItem.ToString() %>" CommandName="Click"/>
                <br />
                <br />
            </asp></itemtemplate>
        </asp>
        <asp  ataPager ID="DataPagerCities" runat="server" PagedControlID="ListViewCities">
                    <fields>
                        <asp :NumericPagerField NextPageText=">>" PreviousPageText="< <" />
                    </asp></fields>
                </asp>
        <asp :ObjectDataSource ID="ObjectDataSourceCities" runat="server" EnablePaging="true"
            SelectCountMethod="GetNumberOfCities" SelectMethod="GetCities" StartRowIndexParameterName="startIndex" TypeName="MM.Core.DAO.AddressDAO"></asp>
    </div>
</asp>

Tags: application, ASP, database session, dynamic web pages, EndRequest, HTTP, linq, mapping technology, NET, object relational mapping