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如何编写多对多关联表的查询

jpa spring-boot hibernate sql java

Nemeth Attila · 技术社区 · 7 年前

我有两个实体,它们之间有多对多的关系。我想在关联表上写一个查询。

Here are the two entities. Craftsmen and Skill.
I want to write a query which selects all Craftsmen with a given skill. 

    @Entity
    @Table(name = "craftsman")
    public class Craftsman {

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        @ManyToMany
        @JoinTable(name = "craftman_skill", joinColumns = @JoinColumn(name = "craftman_id", referencedColumnName = "id"), 
            inverseJoinColumns = @JoinColumn(name = "skill_id", referencedColumnName = "id"))
        private List<Skill> skillList;
    }
        @Entity
        @Table(name = "skill")
        public class Skill {
            @ManyToMany(mappedBy = "skillList")
            @JsonBackReference
            private List<Craftsman> craftmanList;
        }

以下是我尝试过的:

@Query("SELECT c FROM Craftsman c JOIN c.skillList sl WHERE c.skillList.skill_id = :skillId")
    public List<Craftsman> getCraftsmanBySkill(@Param("skillId") Long skillId);

以下是MySql中的查询: 这将获得所有具有id 1技能的工匠:

select c.name from craftsman c, craftman_skill cs 
where cs.craftman_id = c.id 
and cs.skill_id = 1;

以下是我得到的错误:

Caused by: java.lang.IllegalArgumentException: org.hibernate.QueryException: could not resolve property: skill_id of: com.craftsmen.crafts.persistence.Skill [SELECT c FROM com.craftsmen.crafts.persistence.Craftsman c JOIN c.skillList sl WHERE c.skillList.skill_id = :skillId ]
Caused by: org.hibernate.QueryException: could not resolve property: skill_id of: com.craftsmen.crafts.persistence.Skill [SELECT c FROM com.craftsmen.crafts.persistence.Craftsman c JOIN c.skillList sl WHERE c.skillList.skill_id = :skillId ]

2 回复 | 直到 7 年前

Christian Riese 7 年前

我想问题是,你的 Skill 实体确实没有skill\u id或更好的 id 。

你有没有试过 技巧 实体an 身份证件

@Entity
@Table(name = "skill")
public class Skill {
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   private Long id;

   @ManyToMany(mappedBy = "skillList")
   @JsonBackReference
   private List<Craftsman> craftmanList;
}

在您的 Craftsman 实体

@Entity
@Table(name = "craftsman")
public class Craftsman {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToMany
    @JoinTable(name = "craftman_skill", joinColumns = @JoinColumn(name = "craftman_id", referencedColumnName = "id"), 
        inverseJoinColumns = @JoinColumn(name = "skill_id", referencedColumnName = "id"))
    private List<Skill> skillList;
}

然后更改 Query 到

SELECT c FROM Craftsman c JOIN c.skillList sl WHERE sl.id = :skillId

这应该可以奏效。

marc_s 7 年前

您还可以考虑在此处使用JpaRepository:

public interface CraftsmanRepository extends JpaRepository<Craftsman, String> {
    public List<Craftsman> getBySkillListIn(@NotEmpty List<Skill> skillList);

}

这意味着,Jpa通过写入方法名称已经将查询映射到您的SQL查询(如果没有映射,请尝试)

在方法的末尾,“In”表示它应该检查多个值,而不是一个值

在SQL中 In 还可以执行以下操作:

where <condition> And <>condition And <condition> And...