This example uses Hibernate with Groovy using Groovy Grapes.

package demo

import javax.persistence.*
import org.hibernate.cfg.*

// javax.transaction jta.jar added manually to ivy repo
@Grapes([
    @Grab(group='org.hibernate', module='hibernate-annotations', version='3.4.0.GA'),
    @Grab(group='org.slf4j', module='slf4j-simple', version='1.4.2'),
    @Grab(group='hsqldb', module='hsqldb', version='1.8.0.7'),
    @Grab(group='javassist', module='javassist', version='3.4.GA'),
])
@Entity class Book {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    public Long id
    public String author
    public String title
    String toString() { "$title by $author" }
}

def hibProps = [
    "hibernate.dialect": "org.hibernate.dialect.HSQLDialect",
    "hibernate.connection.driver_class": "org.hsqldb.jdbcDriver",
    "hibernate.connection.url": "jdbc:hsqldb:mem:demodb",
    "hibernate.connection.username": "sa",
    "hibernate.connection.password": "",
    "hibernate.connection.pool_size": "1",
    "hibernate.connection.autocommit": "true",
    "hibernate.cache.provider_class": "org.hibernate.cache.NoCacheProvider",
    "hibernate.hbm2ddl.auto": "create-drop",
    "hibernate.show_sql": "true",
    "hibernate.transaction.factory_class": "org.hibernate.transaction.JDBCTransactionFactory",
    "hibernate.current_session_context_class": "thread"
]

def configureHibernate(props) {
    def config = new AnnotationConfiguration()
    props.each { k, v -> config.setProperty(k, v) }
    config.addAnnotatedClass(Book)
    return config
}

def factory = configureHibernate(hibProps).buildSessionFactory()

// store some books
def session = factory.currentSession
def tx = session.beginTransaction()
session.save(new Book(author:'Dierk et al', title:'Groovy in Action'))
session.save(new Book(author:'Craig', title:'Spring in Action'))
tx.commit()

// find some books
session = factory.currentSession
tx = session.beginTransaction()
def books = session.createQuery("from Book").list()
println 'Found ' + books.size() + ' books:'
books.each { println it }
tx.commit()

Which produces this output (logging not shown):

Found 2 books:
Groovy in Action by Dierk et al
Spring in Action by Craig

We can get a little more sophisticated and show a One-to-One relationship as follows:

@Entity class Book {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    public Long id
    @OneToOne
    public Author author
    public String title
    String toString() { "$title by $author.name" }
}

@Entity class Author {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    public Long id
    public String name
}

Where the configureHibernate method needs an additional line:

...
config.addAnnotatedClass(Book)     // existing
config.addAnnotatedClass(Author)   // new
...

And creation would become:

// store some books
def session = factory.currentSession
def tx = session.beginTransaction()
def a1 = new Author(name:'Dierk et al')
session.save(a1)
session.save(new Book(author:a1, title:'Groovy in Action'))
def a2 = new Author(name:'Craig')
session.save(a2)
session.save(new Book(author:a2, title:'Spring in Action'))
tx.commit()

We can get even fancier with a one-to-many association (one way to do it):

@Entity class Book {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    public Long id
    @OneToMany(cascade=CascadeType.ALL)
    public Set<Author> authors
    public String title
    String toString() { "$title by ${authors.name.join(', ')}" }
}

@Entity class Author {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    public Long id
    public String name
}

With creation code like this:

// store some books
def session = factory.currentSession
def tx = session.beginTransaction()
def names1 = ['Dierk', 'Guillaume', 'Jon', 'Andy', 'Paul']
def names2 = ['Craig']
def storeAuthors = { names, hib ->
    Set result = []
    names.each{ def a = new Author(name:it); hib.save(a); result << a }
    result
}
def authors1 = storeAuthors(names1, session)
def authors2 = storeAuthors(names2, session)
session.save(new Book(authors:authors1, title:'Groovy in Action'))
session.save(new Book(authors:authors2, title:'Spring in Action'))
tx.commit()

Which has output like this (logging not shown):

Found 2 books:
Groovy in Action by Paul, Jon, Guillaume, Dierk, Andy
Spring in Action by Craig