JPA:如何过滤关联? [英] JPA: How to filter an association?
问题描述
我的模特:
@Entity
class Person {
@Id
long id;
@OneToMany
Set<Employment> employments = new HashSet<Employment>();
}
@Entity
class Employment {
@Id
long id;
@ManyToOne
Company company;
Date from;
Date until;
}
这是Person
和Company
之间的关联,受时间间隔的限制.
It's an association between a Person
and a Company
that's restricted by a time interval.
我正在寻找一个JPA标准查询,以选择给定时间的所有Person
及其工作.
I'm looking for a JPA criteria query to select all Person
s and their employments at a given time.
预期结果是包含 all 人的List<Person>
,其中每个Person
的集合employments
仅包含符合特定条件的工作(或根本没有工作).
The expected result is a List<Person>
containing all people, where the collection employments
of each Person
contains only employments that match certain criteria (or no emplyments at all).
@Where
不是明智的方法,因为雇用的筛选条件是可变的,例如我想在任何给定时间选择一个人的所有工作.
@Where
is not a sensible approach because the filter criteria for employments is variable, e.g. I would want to select all employments of a person at any given time.
这甚至是合理的事情吗?有什么建议可以采取不同的做法吗?
Is this even a reasonable thing to do? Any suggestions how to do this differently?
推荐答案
不,这不是合理的事情.实体应该表示数据库中的数据,而不是特定查询返回的日期.
No, it's not a reasonable thing to do. An entity is supposed to represent the data that is in the database, and not the date returned by a particular query.
我只需要从Employment
到Person
添加一个ManyToOne关联,然后寻找工作.如果您需要一组人员,则只需遍历各个职业并将每个职业的人员添加到一组中即可.如果您希望在此日期与其工作相关联的人员,则可以使用自定义类或MultiMap<Person, Employment>
.
I would simply add a ManyToOne association from Employment
to Person
, and search for employments. If you need the set of persons, just iterate through the employments and add each employment's person to a Set. If you want the persons associated with their employments at this date, you could use a custom class, or a MultiMap<Person, Employment>
.
String hql = "select employment from Employment employment"
+ " left join fetch employment.person"
+ " where :date between employment.startDate and employment.endDate";
List<Employment> employments = session.createQuery(hql)
.setDate("date", date)
.list();
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