JPA Select "Where IN"

[Barsum]

Q1:

I've made this JPA query that I find really satisfying:

Booking.find("SELECT DISTINCT b FROM Booking b JOIN b.participants AS
t WHERE t = ?", person).fetch();

This query is used for finding all bookings where a given person
participates - and it works just fine.

But now I would like to extend the query so that it will take a list
of employees:

I've tried:

List<Person> persons = Person.findAll();
Booking.find("SELECT DISTINCT b FROM Booking b JOIN b.participants AS
t WHERE t IN ?", persons).fetch();

Which gives me the error:
JPAQueryException occured : Error while executing query SELECT
DISTINCT b FROM Booking b JOIN b.participants AS t WHERE t IN ?:
org.hibernate.HibernateException: Unable to resolve entity name from
Class [java.util.ArrayList] expected instance/subclass of
[models.Person]

I've also tried:

List<Long> ids = new ArrayList<Long>();
ids.add(employee.id);
Booking.find("SELECT DISTINCT b FROM Booking b JOIN b.participants AS
t WHERE t.id IN ?", ids)

Which gives me the error:
JPAQueryException occured : Error while executing query SELECT
DISTINCT b FROM Booking b JOIN b.participants AS t WHERE t.id IN ?:
java.util.ArrayList cannot be cast to java.lang.Long

Heureka! While writing this post, I found a solution. Using the
EntityManager:

List<Person> persons = Person.findAll();
Query query = JPA.em().createQuery("SELECT DISTINCT b FROM Booking b
JOIN b.participants AS t WHERE t IN (?1)");
query.setParameter(1, persons);

So am I using Play JPA wrong? Or is it a missing feature to use WHERE
IN with ? parameteres.

Q2:
Do you have good references where to read about JPA? With lots of
examples :)

[Tex]

Try this 

IN (?1) 

seems that positional parameter worka well with "in clause"...

List<Long> ids = new ArrayList<Long>(); 

ids.add(employee.id); 

List<Booking> bookings = Booking.find("SELECT DISTINCT b FROM Booking b JOIN b.participants AS t WHERE t.id IN (?1)", ids).fetch();

[Barsum]

Thanks Tex - you're absolutely right.

While reading about JPA I came across NamedQueries, and they
supposedly perform better than dynamic queries, so now I'm considering
using EntityManager anyway. Is there any drawbacks to NamesQueries
other than the more cluttered syntax?

[Tex]

Sorry Barsum I cannot answer your question (I'm mainly a Ruby on Rails programmer and I'm not a JPA expert...)