Developing with POJOs: faster and easier - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 17

or join tables. JDO and Hibernate can also run outside of the application server,
which means that you can test your persistent business logic without deploying it
in a server. You can, for example, simply run tests from within your integrated
development environment ( IDE ).

Encapsulating the calls to the persistence framework
Even though Hibernate and JDO provide transparent persistence, some parts of
an application must call the JDO and Hibernate API s to save, query, and delete
persistent objects. For example, TransferService must call the persistence frame-
work to retrieve the accounts and create a BankingTransaction . One approach is
for TransferService to call the persistence framework API s directly. Unfortu-
nately, this would couple TransferService directly to the persistence framework
and the database, which makes development and testing more difficult.
A better approach is to encapsulate the Hibernate or JDO code behind an inter-
face, as shown in figure 1.3. The persistence framework, which in this example is

TransferService

BankingTransaction transfer(fromId, toId, amount)

Account

<<interface>>
Account
Repository

<<interface>>
BankingTransaction
Repository

debit(amount)
credit(amount)

Banking
Transaction

findAccount(id) createTransaction(…)

HibernateBanking
Transaction
Repository

Hibernate
Account
Repository

findAccount(id) createTransaction(…)

Hibernate

Figure 1.3 Using repositories to encapsulate the persistence framework
hides the persistence details from the rest of the application.