What's wrong with this code (Part XII)

In the last post in this series ("what's wrong with this code") we discussed how db4o's reference system remembers which objects have been stored / retrieved.

In this post I'll show you another piece of code that doesn't always work as the developer expects:

class User
{
   public string Name;
   public User Manager;
   public IList Addresses;

   public User(string name, User manager)
   {
      Name = name;
      Manager = manager;
   }
}

class Address
{
   public string Street;

   public Address(string street)
   {
      Street = street;
   }
}  


using (var db = Db4oEmbedded.OpenFile(databaseFileName))
{
   List<Address> addrs = new List();
   addrs.Add(new Address("Street1"));
   addrs.Add(new Address("Street2"));
   User fooManager = new User("Foo") { Addresses = addrs };

   User fooBarManager = new User("FooBar", fooManager);
   User barManager = new User("John Doe",  fooBarManager);
   User user = new User("Adriano",  barManager);
    
   db.Store(user);
}

using (var db = Db4oEmbedded.OpenFile(databaseFileName))
{
   var query = db.Query();
   query.Constrain(typeof (User));
   query.Descend("Name").Constrain("Adriano");
   
   User user = (User) query.Execute()[0];
   Console.WriteLine(user.Manager.Manager.Manager.Addresses[0].Street);
}

Can you see the problem? No, I am not talking about Law of Demeter "violation" :) (By the way, if you are interested in this subject you can find a nice discussion here).

Again, if you have been working with db4o for some time I am sure you already spent some time debugging this kind of issue.

As always, the answer comes in a future post.

Have fun!

Adriano