jpa - 在嵌套字段上使用WHERE进行JPQL查询

Question

我有一个带有事件列表的Java实体类UserBean:

@OneToMany
private List<EventBean> events;

EventBean具有Date变量:

@Temporal(javax.persistence.TemporalType.TIMESTAMP)
private Date eventDate;

现在在UserBean中，我想创建一个NamedQuery，它返回特定范围内的所有日期:

@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")

上面的查询虽然没有编译。我收到此错误:

The state field path 'u.events.eventDate' cannot be resolved to a valid type.

顺便说一下，我使用的是EclipseLink版本2.5.0.v20130507-3faac2b。

我该怎么做才能使此查询正常工作？谢谢。

Answer 1

路径u.events.eventDate是JPQL中的非法构造，因为不允许它通过集合值的路径表达式进行导航。在这种情况下，u.events是一个集合值的路径表达式。在JPA 2.0规范中，这是用以下单词来告知的:

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.

通过使用JOIN可以解决此问题:

SELECT distinct(u) 
FROM UserBean u JOIN u.events e 
WHERE u.name = :someName
      AND e.eventDate > :startDate 
      AND e.eventDate < :endDate