In multi-layered architecture, can I skip the business layer for crud operations?

Question

We have 3 layered application where every call from the service layer goes to the business layer and is persisted by the data layer. Components of each layer can only call the layer below;

However because we have hundreds of entities and we have lots of services related to crud operations so many controversies raised on our team.

Some believe for the sake of maintenance and ease of development it's better to call data access from crud services which just doing crud operation and bypassing business layer.

On the contrary some saying we have to create wrapper for data access of each entity in business layer and call these wrapper from services and never allow services to call data access layer.

In your idea which way we should take? Is it ok for crud services to call data accesses and bypassing business layer?

Answer 1

If there is no business logic to perform, there is no reason to enforce a business layer. The 3-tier architecture is not an arcane protocol, just a best practice that was formed assuming business processing.

In a current application we are often accessing DAOs directly from JSF controllers when there is no business process involved. The idea was given by a java champion who stressed the idea that simplicity is paramount.

If you are worried about future modifications that may require adding business logic. I think of the issue this way: The additional business logic would be added to the business layer anyway, including data access, so there is no difference here.

CRUD code is mostly very simple. So the change in the service would amount to reroute a single call or a couple of calls fron the DAO to an EJB - a simple refactoring. The CRUD code itself would still remain, but will be pushed into the EJB - another simple refactoring.

This is not perfect, but IMO better then the alternative: having an empty indirection layer. This adds complexity that serves no purpose. The business object would do nothing but forward the calls to the DAO.

There are two code smells that I think apply in this case: contrived complexity and feature envy.

I am not saying that DA in the business layer is somehow a code smell. What I mean is that having a business object that does nothing else but proxy the DAO is a smell. It's the same with complexity - an added data structure / architectural layer that serves no own purpose - there seems to be a DAL in your application already.

Another aspect for your consideration would be - how surprising is it for a developer to see a service that uses a DAO directly? Having 5 services where 2 of them access DAO directly is different from having 100 services where only one service accesses the DAOs directly.

In the first case the code simplicity would outweigh the added conceptual complexity (2 concepts for a single thing), in the second case, I would rather stick with the business layer - the surprise (also called the WTF-effect ;) of doing it differently just once would be too big.

Answer 2

In my opinion, having call CRUD services bypassing the business layer will start converting the current service layer into a business layer as you increase the functionality. So your service layer will act as the business layer too, if you are fine with it.

In most cases, you deal with an entity and probably that could involve many data layer crud calls, on one update for example. A business layer is recommended for this purpose. And business layer is the place to execute any business rules, caching or call other business services if required. This will keep the upper layer simple and pass through.

Answer 3

I will not bypass the business layer. Even though it might look like you are only proxying the call for the DAL into the BL, and even though this may be a case of very simple CRUD operation, the BL can encapsulate the validation logic required for the operation. Validation logic can be performed on the BL and proxying to DAL will only be performed if the validation conditions are met.

Answer 4

If you only have CRUD operations, you can use Data Services to publish your data sets as web services. A good example to this is WSO2 Data Services http://wso2.com/products/data-services-server/