在 Spring Data JPA 中连接两个表实体 [英] Joining two table entities in Spring Data JPA

问题描述

我想写一个类似 SELECT * FROM Release_date_type a LEFT JOIN cache_media b on a.id=b.id 的查询.我是 Spring Data JPA 的新手.我不知道如何为 Join 查询编写实体.这是一个尝试:

I want to write a query like SELECT * FROM Release_date_type a LEFT JOIN cache_media b on a.id=b.id. I am new to Spring Data JPA. I don't know how to write entities for Join query. Here is an attempt:

@Entity
@Table(name = "Release_date_type")
public class ReleaseDateType {

    @Id
    @GeneratedValue(strategy=GenerationType.TABLE)
    private Integer release_date_type_id;
    // ...
    @Column(nullable = true) 
    private Integer media_Id;
    // with getters and setters...
}

另一个实体是:

@Entity
@Table(name = "Cache_Media")
public class CacheMedia {

    @Id
    @GeneratedValue(strategy=GenerationType.TABLE)
    private Integer id;
    // ...
    private Date loadDate; //with the getter and setter ..
}

我想写一个crudRepository接口比如

public interface ReleaseDateTypeRepository extends CrudRepository<ReleaseDateType, Long>{
    @Query("SELECT * FROM Release_date_type a LEFT JOIN cache_media b on a.id=b.id")
    public List<ReleaseDateType> FindAllWithDescriptionQuery();
}

推荐答案

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对于您的具体示例，如果您想建立一对一关系，您应该更改 ReleaseDateType 模型中的下一个代码:

For your specific example, if you want to do a one-to-one relationship, you should change the next code in ReleaseDateType model:

@Column(nullable = true) 
private Integer media_Id;

用于:

@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name="CACHE_MEDIA_ID", nullable=true)
private CacheMedia cacheMedia ;

在 CacheMedia 模型中你需要添加:

and in CacheMedia model you need to add:

@OneToOne(cascade=ALL, mappedBy="ReleaseDateType")
private ReleaseDateType releaseDateType;

然后在您的存储库中，您应该替换:

then in your repository you should replace:

@Query("Select * from A a  left join B b on a.id=b.id")
public List<ReleaseDateType> FindAllWithDescriptionQuery();

作者:

//In this case a query annotation is not need since spring constructs the query from the method name
public List<ReleaseDateType> findByCacheMedia_Id(Integer id); 

或通过:

@Query("FROM ReleaseDateType AS rdt WHERE cm.rdt.cacheMedia.id = ?1")    //This is using a named query method
public List<ReleaseDateType> FindAllWithDescriptionQuery(Integer id);

或者，如果您更喜欢使用 @OneToMany 和 @ManyToOne 关系，您应该更改 ReleaseDateType 模型中的下一个代码:

Or if you prefer to do a @OneToMany and @ManyToOne relation, you should change the next code in ReleaseDateType model:

@Column(nullable = true) 
private Integer media_Id;

用于:

@OneToMany(cascade=ALL, mappedBy="ReleaseDateType")
private List<CacheMedia> cacheMedias ;

在 CacheMedia 模型中你需要添加:

and in CacheMedia model you need to add:

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="RELEASE_DATE_TYPE_ID", nullable=true)
private ReleaseDateType releaseDateType;

然后在您的存储库中，您应该替换:

then in your repository you should replace:

@Query("Select * from A a  left join B b on a.id=b.id")
public List<ReleaseDateType> FindAllWithDescriptionQuery();

作者:

//In this case a query annotation is not need since spring constructs the query from the method name
public List<ReleaseDateType> findByCacheMedias_Id(Integer id); 

或通过:

@Query("FROM ReleaseDateType AS rdt LEFT JOIN rdt.cacheMedias AS cm WHERE cm.id = ?1")    //This is using a named query method
public List<ReleaseDateType> FindAllWithDescriptionQuery(Integer id);

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