I am not dead. Not yet

Warning: Personal content ahead

I can hear someone screaming already: but it really looked like you have died! :)

Well, you know, I have been having to much work fun lately.

Also, more or less 7 months ago, I and my wife decided to start a new project, daughter 2.0, and since then we have been working hard to get the environment ready to the deployment (there are too many details in such projects deployment). 

At this stage we can say that the project is growing as expected and that we are looking forward to the deployment date.

As always we expect the maintenance phase to consume much more time/resources than the development phase, but we are more than willing to do the required investment so the project will be able to meet its goals; after all, this is our baby :).

Last but not least, as you can see, I am actually alive :). So, bear with me! As soon as I get some spare time I'll do some more posts!

Good to get back to posting!

See you all.

Did you know ? (Part I) - Executing sub-queries

With this post I want to start a series of "Did you know?" regarding programing related topics and db4o features / usage patterns that may not be well known.

As the first one, take a look in the following code:
 

class Address
{
  public Address(string streetName)
  {
     StreetName = streetName;
  }

  public string StreetName { get; set; }

  public override string ToString()
  {
     return "Address: " + StreetName;
  }
}

class Person
{
   public Person(string name, Address address)
   {
       Name = name;
      _address = address;
   }

   public Address Address
   {
      get { return _address; }
      set { _address = value; }
   }

   public string Name { get; set;}

   public override string ToString()
   {
      return "Person: " + Name;
   }
   private Address _address;
}

using (var db = Db4oEmbedded.OpenFile(databaseFileName))
{
   db.Store(new Person("Adriano", new Address("You know where I live")));
   db.Store(new Person("Sulivan", new Address("Monstropolis")));
   db.Store(new Person("Mike", new Address("Who cares?")));
   db.Store(new Address("Foo address"));

   IQuery q =  db.Query();
   q.Constrain(typeof(Person));
   IQuery descendantQuery = q.Descend("_address");
   
   foreach(var result in descendantQuery.Execute())
   {
      Console.WriteLine(result);
   }
}

What do you think will be the result?

Well, it will return all addresses objects that have a Person as a parent, i.e, "foo address" will not be retrieved/shown! 

You can even specify constrains in both queries (getting the addresses for persons with a specific name!).

Note that this does not work for fields with value type semantics (basically any primitive value, enums [in .Net], string, etc.).

Do you have any db4o topic that, in your opinion, is commonly misunderstood and you would like to discuss? Please, let us know :)



Have fun!

Adriano

What's wrong with this code(Part XI) - Answer

In this post I presented the following code.

using Db4objects.Db4o;
using Db4objects.Db4o.Linq;
using System.Linq;

class Item
{
public string Name { get; set; }
public Item Father { get; set ; }
}

public class Test
{
 private const string DatabaseFile = "wwwtc1.odb";
 private static void Main()
 {
     Item item1 = new Item { Name = "Adriano" };
     using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
     {
         db.Store(item1);
     }

     using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
     {
         Item item2 = new Item {Name = "Carol",  Father = item1 };
         db.Store(item2);
     }
 }
}

And asked what was wrong with it (and commenter "tehlike" got it :). 


In line 20 we close the database (technically, the using statement will call IDisposable.Dispose() method on the object container which in turn will close it), reopen it at line 22 and finally add a new object (item2) at line 25.  

Take a closer look in the program and you'll see that item2 references item1 which was stored in the database previously. As the documentation states (here and here), db4o uses a reference system to "memorize" which objects are known to be stored in the database (relying on object identity when checking if a given object is already present in this reference system). 

When a database is opened its reference system is empty, so when storing item2 db4o will store item1 again (after all we re-opened the database, so there are no objects in the reference system and both objects are considered as "new", i.e, need to be inserted into the database),  i.e, now we have 2 instances of class Item with the same contents in the database.

What can a developer do to avoid this behavior? Easy, just let the just opened object container know that item1 has already been persisted by retrieving it before referencing it from item2 :) 

using Db4objects.Db4o;
using Db4objects.Db4o.Linq;
using System.Linq;

class Item
{
  public string Name { get; set; }
  public Item Father { get; set ; }
}

public class Test
{
 private const string DatabaseFile = "wwwtc1.odb";
 private static void Main()
 {
     Item item1 = new Item { Name = "Adriano" };
     using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
     {
         db.Store(item1);
     }

     using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
     {
         item1 = (from Person p in db where p.Name == "Adriano").Single();
         Item item2 = new Item {Name = "Carol",  Father = item1 };
         db.Store(item2);
     }
 }
}

Another possible solution (with less performance impact) would be to not close/reopen the database so item1 would be kept in the reference system and db4o would understand that it does not need to store this object again.

using Db4objects.Db4o;
using Db4objects.Db4o.Linq;
using System.Linq;

class Item
{
  public string Name { get; set; }
  public Item Father { get; set ; }
}

public class Test
{
  private const string DatabaseFile = "wwwtc1.odb";
  private static void Main()
  {
     Item item1 = new Item { Name = "Adriano" };
     using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
     {
         db.Store(item1);
         Item item2 = new Item {Name = "Carol",  Father = item1 };
         db.Store(item2);
     }
  }
}

Have fun!

Adriano

What's wrong with this code(Part XI) ?

Since I joined db4o I'm actively following our forums and trying to help developers to get their questions / issues answered.

Starting with this post I want to present the most recurring topics (don't know exactly how many) in the format of "What's wrong with this code".

But before we start you may be wondering where are the other parts (since this is titled as Part XI, where are parts from I to X). Well, they do exists in the portuguese posts (titled as "O que esta errado com este código (Parte ?)") so I decided to continue with the numbering schema ;)

Ok, for this first one, take a look in the following code:

using Db4objects.Db4o;
using Db4objects.Db4o.Linq;
using System.Linq;

class Item 
{
 public string Name { get; set; }
 public Item Father { get; set ; }
}

public class Test
{
    private const string DatabaseFile = "wwwtc1.odb";
    private static void Main()
    {
        Item item1 = new Item { Name = "Adriano" };
        using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
        {
           db.Store(item1);
        }
  
        using (var db = Db4oEmbedded.OpenFile(DatabaseFile))
        {
          Item item2 = new Item {Name = "Carol",  Father = item1 };
          db.Store(item2);
        }  
    }
}

If you have done some work with db4o you probably will easily spot the problem.

I'll provide the answer in a future post.

Have fun!

Going to ICOODB

Hi.

Next week I'll attend the second international conference on object databases in Zürich. Woow!

I am sure it will be really amazing moments; I'll have the chance to meet db4o fellows face to face again, to attend to interesting talks, to talk to db4o community members and db4o enthusiasts! Since most db4o team members will meet at Zurich we're taking the chance to discuss db4o directions also. 

Of course, visiting another country (even though being a work trip) and getting in touch with a different culture will be really a great experience. 

My friends knows how much I like chocolates, so I am sure I am going to get some extra weight :)


The not so nice part is that I'll have a 14 hours flight from Brazil to Switzerland and I must admit that I am a bit anxious with the latest flight news (the interesting thing is that I am almost sure I'll have some nice live pair programing session with my good friend Rodrigo while we wait for our flight).


The worst part is to be far from my wife / daughter (I'll miss my daughter's school presentation).


For those that I'll meet at Zurich, see you soon. For everyone else, see you in this blog :)


Best

Adriano

Hexadecimal Control Viewer DotNet

Hi!

Some time ago I started developing a .Net application that requires a control to display hexadecimal values; considering that I could not find a suitable one (and also, that I do suffer for the NIH syndrome) I decided to write one myself.

After some time developing the application I lost interest (since I moved jobs and the main goal of the application was to make my previous job easier) and now it is kind of abandoned but I think that the hexadecimal control may be handy for some developers.

Here is a list of this control's main features:

• Find
  
• Print / Print Preview
  
• Ranges: It's possible to specify that some byte ranges should be displayed with a specific color for instance
• Selection
  
• Cut/Past

Since the application is released under an open source license anyone can grab the sources, or, if you are interested I can add you as a developer on source forge!

Best

Adriano

Elementary my dear Watson

In my last post I was talking about some issues I found while trying to automate the process of launching  a web browser, navigating to a specific page and grabbing some results.

I do have a bunch of stickers with sayings: "Works on My Machine (tm)" but this time I could not even use one of them since even in my machine it refused to work :(. So, the goal of this post is to explain the reasons I got so much pain...

Since an image speak for 1000 words, here it is:

I am sure you already got it. As you can see I am running Vista x64 on my machine and, as explained here and here, when launching IE through Quick Launcher, the 32 bits version is the one that gets launched; by the other hand, when started through COM the bitness of the launcher defines which IE version gets started (32 or 64 bits).
 
In my case (remember, my first approach was to use a JScript script to automate IE) I was trying to start it from Windows console application (cmd.exe) that happens to be a 64 bit application. That's explain why IE insisted to offer me to install Silverlight; on IE 64 bit version I had not installed it (actually, unfortunately, as of today, Silverlight has support for this platform).

The next step was to figure out why my C# application (the one that hosts the WebBrowser control) was failing with the same symptoms. To be sincere, since I had already faced similar issues when using COM components on .Net applications in x64 machines, this one was a lot easier: Again, as explained here, by default VS sets your application to run on whichever processor architecture (regarding to bitness) you throw at it, i.e, it sets the "target platform" to "Any CPU":

That's mean that in a 64 bit machine (like mine) this application will run in 64 bit CLR, hence IE x64 being launched! Peace of cake :). All I had to do was to set this configuration to "x86". Finally my day would be a little less frustrating than I anticipated it to be.

Really fun, don't you agree?

For the next post I am planing to continue on this subject: 32 x 64 bits developer's pitfalls.

Have fun!

Adriano