Question

我有2个班级：

@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;
}

我试图按模型查询人物。运行以下代码失败，即使表之间的连接是明确的：

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

当已定义实体之间的关系时，您可以使用join fetch语法：

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

Answer 2

mo.cars是一个集合。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

与往常一样，the relevant documentation。

在使用JPA关系查询时非法尝试取消引用集合

2 个答案: