在使用JPA关系查询时非法尝试取消引用集合

Question

我有2个班:

@Table(name = "PEOPLE")
@Entity
class Person {
  @OneToMany(mappedBy = "owner")
  Set<Car> cars;
}
@Table(name = "CARS")
@Entity
class Car {
  @ManyToOne
  @JoinColumn(name = "OWNER_ID", referencedColumnName = "ID")
  Person owner;
  @Column(name = "MODEL")
  String model;
}

我正在尝试按模型查询人物.即使表之间的连接是明确的,运行以下代码也会失败:

select mo from Person mo where mo.cars.model = ?

错误是:

org.hibernate.QueryException: illegal attempt to dereference collection [...] with element property reference [model] [select mo from Person mo where mo.cars.model = ?]

知道如何解决这个问题吗？

Answer 1

当已经定义了实体之间的关系时,您可以使用以下join fetch语法:

select mo from Person mo join fetch mo.cars c where c.model = ?

Answer 2

mo.cars是一套.您无法访问Set的model属性,因为它没有.您需要加入:

 select p from Person p 
 inner join p.cars car
 where car.model = :model

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