Domain Layer

A better design option is to put the rules where they belong, inside the domain objects. If a business rule logic spans two or more Entity objects, then it should become part of a Service class.

Business Rules

Business rules are an important part of the business domain.Business rules typically fall into the following categories:

• Data Validation
• Data Transformation
• Business Decision-Making
• Process Routing (Work-Flow Logic)

A better design option is to put the rules where they belong, inside the domain objects. If a business rule logic spans two or more Entity objects, then it should become part of a Service class.

Repositories

DAO methods are fine-grained and closer to the database while the Repository methods are more coarse-grained and closer to the domain. Also one Repository class may have multiple DAO's injected. Repositories and DAO's keep the domain model decoupled from dealing with the data access and persistence details.

The domain objects should depend only on Repository interfaces. This is the reason why injecting the Repository instead of a DAO results in a much cleaner domain model.