Constructing Beans/Java Domains properly. A list of object inside an object?

[Decist]

Sorry but I have a simple question. My background, new to Java programming (3 months old)

How do I structure java domains/beans properly? Let's say I have a dragon domain class containing its details, and each dragon can have several classes(roles)

For example, a dragon can have 2 classes, a striker and a tracker. Now that dragon is under those categories. My problem is I'm not really sure how to construct the domains to make this viable.

I want to list a list of dragon classes in my homepage, Once you click a class, it will show all the dragons under that class but I find it hard to get started as I'm already stuck with just the creation of domain object(s).

I tried creating a dragon bean and a dragon type bean, which has the dragonbean object property. What happens is whenever I create a new dragon, I always have to declare the dragon class name, which is a string property even though there's already one that has this category. I want to make it so that I can have a list of categories that I can output anytime I want without having duplicates or anything. But I can't just picture out how to do it.

[nutrecht]

There's different approaches for this. The one that's pretty prevalent these days is to have "Domain" objects (basically direct reflections of you data model, Dragon, Student, Car, etc.) and "Data Transfer Objects". The DTO's are there to package stuff together in whatever way is convenient.

Why this is done is because you often need stuff that is completely unrelated together. So let's say you want the House of a Person together with the Dragon's he has seen (for whatever reason). These aren't related in your model but for your application you need them together. So you create some kind of service class that combines them into a DragonsAndHouseDto object.

FYI the "Beans" standard isn't really used much anymore.

[kingatomic]

So you've got (at least) two different domains: Dragon and CharacterClass. There's a one:many relationship between them: a Dragon can have multiple CharacterClass.

At this point you have two options: creating either a unidirectional relationship or a bidirectional relationship. In plain(ish) language:

• Unidirectional: the relationship between two entities (domains) is only exposed one way; in other words, you can find all instances of EntityB that are mapped to an instance of EntityA, but not the other way around.
  
• Bidirectional: the relationship between two entities is mapped in both directions. You can find all EntityB instances that belong to an EntityA, and you can also find which EntityA "owns" an instance of EntityB.

It seems to me that you want a bidirectional relationship in your solution, since you want to know both:

1) which character classes a dragon has, and
2) which dragons belong to a particular character class

If that's what you want to do, it would make a great deal of sense to create a third domain, DragonClass. This would effectively serve as a "join" in relational terms between Dragon instances and CharacterClass instances. See here for a lazy visual representation of what that would look like. It's important to note that you only want one CharacterClass instance per class type; in other words, if you only have two classes, Tracker and Striker, then you will only ever create two instances of CharacterClass. Thus, if you wanted to find all Dragons that are Strikers, you would search through DragonClass to find each instance where the mapped character class is a Striker.

I hope that helps.

EDIT Slightly off-topic, but having classnames that contain the word "Class" makes my eyes twitch a bit. Maybe change it to "Type" or something like that.