Q:

JPQL query with WHERE on nested fields

I have a java entity class UserBean with a list of events:
@OneToMany
private List<EventBean> events;

EventBean has Date variable:
@Temporal(javax.persistence.TemporalType.TIMESTAMP)
private Date eventDate;

Now in UserBean I want to create a NamedQuery that returns all dates that fall within a specific range:
@NamedQuery(name="User.findEventsWithinDates",
            query="SELECT u.events FROM UserBean u WHERE u.name = :name AND u.events.eventDate > :startDate AND u.events.eventDate < :endDate")

The above query does not compile though. I get this error:
The state field path 'u.events.eventDate' cannot be resolved to a valid type.

By the way, I use EclipseLink version 2.5.0.v20130507-3faac2b.
What can I do to make this query work? Thanks.

A:

Path u.events.eventDate is an illegal construct in JPQL, because it is not allowed to navigate via a collection valued path expression. In this case u.events is a collection valued path expression. In JPA 2.0 specification this is told with following words:

It is syntactically illegal to compose a path expression from a path
  expression that evaluates to a collection. For example, if o
  designates Order, the path expression o.lineItems.product is illegal
  since navigation to lineItems results in a collection. This case
  should produce an error when the query string is verified. To handle
  such a navigation, an identification variable must be declared in the
  FROM clause to range over the elements of the lineItems collection.

This problem can be solved by using JOIN:
SELECT distinct(u) 
FROM UserBean u JOIN u.events e 
WHERE u.name = :someName
      AND e.eventDate > :startDate 
      AND e.eventDate < :endDate

