Overview of persisting a domain model - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 119

Table 4.2 shows the key methods defined by the Session and PersistenceMan-
ager interfaces.

Table 4.2 Examples of JDO PersistenceManager and Hibernate Session methods

Hibernate Session JDO PersistenceManager

Making an object persistent save() makePersistent()

Loading an object load() getObjectById()

Deleting an object delete() deletePersistent()

Creating a query createQuery()

createNamedQuery()

newQuery()
newNamedQuery()

Accessing the transaction
object

beginTransaction() currentTransaction()

Closing the connection close() close()

As you can see, Session and PersistenceManager define methods with very similar
purposes. For example, the save() and makePersistent() methods persist an
object, and the load() and getObjectById() methods load the specified instance.
There are also methods for creating queries, accessing the transaction object, and
closing the connection.

4.3.3 Query language

Hibernate and JDO provide several options for executing queries. An application
can use either object queries , which are queries expressed in terms of objects, or
SQL native queries , which are written in SQL . JDO and Hibernate provide a textual
query language for writing object queries. In addition, Hibernate has what are
called criteria queries , which are nontextual queries.

Object queries
Object queries are the easiest to use because they take full advantage of the ORM
framework. JDO and Hibernate each have a textual query language for object que-
ries. JDO object queries are written in JDO Query Language ( JDOQL ), whose syn-
tax is based on Java expressions; Hibernate provides Hibernate Query Language
( HQL ), whose syntax is similar to SQL . JDOQL and HQL queries usually return per-
sistent objects, but you can also write projection queries , which return DTO s and
other values.