无法从类型 [java.lang.Object[]] 转换为类型 [@org.springframework.data.jpa.repository.Query答案

【问题标题】：Failed to convert from type [java.lang.Object[]] to type [@org.springframework.data.jpa.repository.Query无法从类型 [java.lang.Object[]] 转换为类型 [@org.springframework.data.jpa.repository.Query
【发布时间】：2020-03-29 17:08:11
【问题描述】：

我有使用 JPA/Hibernate、MySQL 的 spring boot 项目。我有三个具有多对多关系的道类。

Poko 类看起来像这样

产品

@Entity
@Table(name = "product")
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false, columnDefinition = "integer")
    private Integer id;
    @Column(name = "name")
    private String name;
    @Column(name = "price")
    private Double price;

    @ManyToMany(cascade = {
            CascadeType.PERSIST,
            CascadeType.MERGE
    })
    @JoinTable(
            name = "product_extra",
            joinColumns = @JoinColumn(name="product_id"),
            inverseJoinColumns = @JoinColumn(name="extra_id")
    )
    private List<Extra> extras = new ArrayList<>();

  //constructor getters and setters
}

产品附加

@Entity
@Table(name = "product_extra")
public class ProductExtra {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false, columnDefinition = "integer")
    private Integer id;
    @Column(name = "product_id")
    private Integer productId;
    @Column(name = "extra_id")
    private Integer extraId;

   //constructor getters and setter
}

额外

@Entity
@Table(name = "extra")
public class Extra {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", unique = true, nullable = false, columnDefinition = "integer")
    private Integer id;
    @Column(name = "name")
    private String name;
    @Column(name = "price")
    private Double price;

    @ManyToMany(mappedBy = "extras")
    private List<Product> products = new ArrayList<>();

    //constructor getters and setters
}

带有查询的额外存储库

public interface ExtraRepository extends JpaRepository<Extra, Integer> {
    @Query("SELECT e.id, e.name, e.price FROM Extra e INNER JOIN ProductExtra pe ON e.id = pe.extraId WHERE pe.productId = ?1")
    List<Extra> findExtraById(Integer productId);
}

我的控制器中的映射

@GetMapping("/product/{productId}")
    public List<Extra>getExtraById(@PathVariable("productId") final Integer productId){
        return extraRepository.findExtraById(productId);
    }

我正在尝试进行多对多查询以选择每个产品中的附加功能，但是我收到此错误Failed to convert from type [java.lang.Object[]] to type [@org.springframework.data.jpa.repository.Query 错误消息令人惊讶地还包含我想要的结果。不知道哪里做错了

【问题讨论】：

标签： mysql hibernate spring-boot jpa

【解决方案1】：

删除SELECT 子句：

@Query("FROM Extra join e.productExtra WHERE pe.productId = ?1")

另外请记住，您不是编写 SQL 查询，而是在对象上工作，因此对于连接，您使用映射的属性

【讨论】：