Rich vs Anemic Domain Model
I am deciding if I should use a Rich Domain Model over an Anemic Domain Model, and looking for good examples of the two.
I have been building web applications using an Anemic Domain Model, backed by a Service --> Repository --> Storage layer system, using FluentValidation for BL validation, and putting all of my BL in the Service layer.
I have read Eric Evan's DDD book, and he (along with Fowler and others) seems to think Anemic Domain Models are an anti-pattern.
So I was just really wanting to get some insight into this problem.
Also, I am really looking for some good (basic) examples of a Rich Domain Model, and the benefits over the Anemic Domain Model it provides.
Answer
The difference is that an anemic model separates logic from data. The logic is often placed in classes named **Service, **Util, **Manager, **Helper and so on. These classes implement the data interpretation logic and therefore take the data model as an argument. E.g.
public BigDecimal calculateTotal(Order order){
...
}
while the rich domain approach inverses this by placing the data interpretation logic into the rich domain model. Thus it puts logic and data together and a rich domain model would look like this:
order.getTotal();
This has a big impact on object consistency. Since the data interpretation logic wraps the data (data can only be accessed through object methods) the methods can react to state changes of other data -> This is what we call behavior.
In an anemic model the data models can not guarantee that they are in a legal state while in a rich domain model they can. A rich domain model applies OO principles like encapsulation, information hiding and bringing data and logic together and therefore a anemic model is an anti pattern from an OO perspective.
For a deeper insight take a look at my blog https://www.link-intersystems.com/blog/2011/10/01/anemic-vs-rich-domain-models/