问题
Firstly it is possible that I am asking something that has been asked and answered before but I could not get a search result back . Okay generally (or always so far:) ) We define transactional annotations on service layer typical spring hibernate crud is usually
Controller->Manager->Dao->Orm .
I now have a situation where I need to choose between the domain model based on client site . Say client A is using my domain model all is good but then an other client site would give me a web service and not be using our domain model .
Which layer should I be replacing . I believe it has to be DAO which will be getting me data from web service and sending it back.i.e two separately written DAO layers and plugged in based on scenario .
I have now realized that we have been doing tight coupling (if there is such a thing or say not having loose coupling) when we put @Transactional in Service layer . So many brains can not be wrong or are they (I doubt it).
So question is "Where should "@Transactional" be place Service Layer or DAO ?" and is it service layer downwards I should be replacing .
回答1:
Ideally, Service layer (Manager) represents your business logic and hence it should be annotated with @Transactional.
Service layer may call different DAOs to perform DB operations. Lets assume a situation where you have 3 DAO operations in a service method. If your 1st DAO operation failed, other two may be still passed and you will end up inconsistent DB state. Annotating Service layer can save you from such situations.
回答2:
You are going to want your services to be transactional. If your DAOs are transactional, and you call different DAOs in each service, then you would have multiple transactions, which is not what you want. Make the service calls transactional, and all DAO calls inside those methods will participate in the transactions for the method.
回答3:
i will suggest to put @Transactional in Service layer methods since we can have multiple DAO implementations. by using this we can made our services will be transactional. refer
best practice is to use A generic BasicService to offer common services.
The Service is the best place for putting @Transactional, service layer should hold the detail-level use case behavior for a user interaction that would logically go in a transaction. in this way we can have maintain separation between web application code and business logic.
There are a lot of CRUD applications that don't have any significant business logic, for them having a service layer that just passes stuff through between the controllers and data access objects is not useful. In these cases we can put transaction annotation on Dao.
So in practice you can put them in either place, it's up to you.
By having multiple calls in your service you need @Transactional in service. different calls to service will execute in different transactions if you put @Transactional in service.
回答4:
It's of a personal choice based on application types, if application is layerd across many modules and majority of operations are @CRUD based ,then having @transactional annotation at service level makes more sence.. engine type application like schedulers , job servers,@etl report apps, where sessions and user concept does not exists, then propagational transaction at context level is most suitable... we should not end up creating clusterd transactions by putting @transactional every where ending up transactional anti patters...anyways for pragmatic transaction control JTA2 is most suitable answer...again it depends on weather you can use it in a given situations...
回答5:
You should use @Transactional at service layer, if you want to change the domain model for client B where you have to provide the same data in a different model,you can change the domain model without impacting the DAO layer by providing a different service or by creating a interface and implementing the interface in different model and with the same service populate the model based on the client.This decision is based on the business requirement and the scope of the project.
来源：https://stackoverflow.com/questions/3886909/where-should-transactional-be-place-service-layer-or-dao