mysql - JPA/Hibernate 中查询返回 null，但 mysql 中不返回 null

Question

我正在执行一个查询，但它返回null，但是当我在 sql 行 cmd 中尝试时，它返回结果。

这是我的实体:

@Entity
@Table(name = "appel_offre", catalog = "ao")
public class AppelOffre implements java.io.Serializable {

    private Integer idAppelOffre;
    ...
    private Admin userValidation;
    private Admin userSaisie;
    private Admin userControle;

    ....

    public AppelOffre(Integer idAppelOffre,Admin userSaisie,Admin userControle,Admin userValidation) {
        System.out.println("users"); // <-- code not executed
        this.idAppelOffre = idAppelOffre;
        this.userSaisie = userSaisie;
        this.userControle = userControle;
        this.userValidation = userValidation;

    }

我的查询是:

@Query(" select new AppelOffre( ao.idAppelOffre , ao.userSaisie , ao.userControle , ao.userValidation )  from AppelOffre  ao "
 AppelOffre  FindAOwithUsers(@Param("idao") Integer idao);

生成的查询是:

select appeloffre0_.ID_APPEL_OFFRE as col_0_0_, appeloffre0_.USER_SAISIE as col_1_0_, appeloffre0_.USER_CONTROLE as col_2_0_, appeloffre0_.USER_VALIDATION as col_3_0_ 
from ao.appel_offre appeloffre0_ 
inner join ao.admin admin1_ on appeloffre0_.USER_SAISIE=admin1_.ID 
inner join ao.admin admin2_ on appeloffre0_.USER_CONTROLE=admin2_.ID 
inner join ao.admin admin3_ on appeloffre0_.USER_VALIDATION=admin3_.ID 
where appeloffre0_.ID_APPEL_OFFRE=?

我知道问题出在内部联接上，它们必须是左联接，因为在我的数据库中只有USER_SAISIE，它不是null。

我尝试用左连接这样:

@Query(" select new AppelOffre( ao.idAppelOffre , ao.userSaisie , ao.userControle , ao.userValidation )  from AppelOffre  ao "
        + " left join ao.userSaisie  "
        + " left join ao.userControle  "
        + " left join ao.userValidation  "
         + " where ao.idAppelOffre = :idao ")
 AppelOffre  FindAOwithUsers(@Param("idao") Integer idao);

但它在查询中生成了双倍:

Hibernate: select appeloffre0_.ID_APPEL_OFFRE as col_0_0_, appeloffre0_.USER_SAISIE as col_1_0_, appeloffre0_.USER_CONTROLE as col_2_0_, appeloffre0_.USER_VALIDATION as col_3_0_ 
from ao.appel_offre appeloffre0_ 
left outer join ao.admin admin1_ on appeloffre0_.USER_SAISIE=admin1_.ID 
left outer join ao.admin admin2_ on appeloffre0_.USER_CONTROLE=admin2_.ID 
left outer join ao.admin admin3_ on appeloffre0_.USER_VALIDATION=admin3_.ID 
inner join ao.admin admin4_ on appeloffre0_.USER_SAISIE=admin4_.ID 
inner join ao.admin admin5_ on appeloffre0_.USER_CONTROLE=admin5_.ID 
inner join ao.admin admin6_ on appeloffre0_.USER_VALIDATION=admin6_.ID 
where appeloffre0_.ID_APPEL_OFFRE=?

而且我的构造函数中的 System.out.println("users"); 也没有显示。

为什么这不起作用以及如何解决这个问题

Answer 1

由于查询未返回任何结果，因此未调用构造函数。由于使用了内部联接，它没有返回任何结果，你是对的。要使其工作，请使用左连接，如下所示

@Query(" select new AppelOffre(ao.idAppelOffre, us, uc, uv)  from AppelOffre  ao left join ao.userSaisie us left join ao.userControle uc left join ao.userValidation uv "