休眠@OneToMany 关系

Question

@OneToMany 关系有些问题。 第一个实体代表某种商品。

@Entity(name = "ARTIQULE")
public final class ArtiquleEntity extends CustomEntity{

@Id
@Column(name = "ID")
public Long id;

@NotNull
@Column(name = "METRIC_ID")
public Long metricId;

@NotNull
@Column(name = "STATUS_ID")
public Long statusId;

@NotNull
@Column(name = "NAME")
public String name;

@NotNull
@Column(name = "SHORT_NAME")
public String shortName;

@NotNull
@ManyToOne
@JoinColumn(name = "GROUP_ID")
public ArtGroupEntity artGroup;
}

二是商品分组

@Entity(name = "AR_GROUP")
public final class ArtGroupEntity extends CustomEntity {

@Id
@Column(name = "ID")
public Long id;

@NotNull
@Column(name = "GROUP_ID")
public Long groupId;

@NotNull
@Column(name = "STATUS_ID")
public Long statusId;

@NotNull
@Column(name = "NAME")
public String name;

@NotNull
@Column(name = "L")
public Integer left;

@NotNull
@Column(name = "R")
public Integer right;

@NotNull
@OneToMany(mappedBy = "artGroup", fetch = FetchType.EAGER)
public List<ArtiquleEntity> artiquleEntities;
}

当我进行“从 AR_GROUP 列表中选择列表”之类的选择时。 Hibernate为每个组创建一个选择，为什么不使用外连接？ 或者是不可能的。

Hibernate: select artgroupen0_.ID as ID1_0_, artgroupen0_.GROUP_ID as GROUP_ID2_0_, artgroupen0_.L as L3_0_, artgroupen0_.NAME as NAME4_0_, artgroupen0_.R as R5_0_, artgroupen0_.STATUS_ID as STATUS_I6_0_ from AR_GROUP artgroupen0_
Hibernate: select artiquleen0_.GROUP_ID as GROUP_ID2_1_0_, artiquleen0_.ID as ID1_1_0_, artiquleen0_.ID as ID1_1_1_, artiquleen0_.GROUP_ID as GROUP_ID2_1_1_, artiquleen0_.METRIC_ID as METRIC_I3_1_1_, artiquleen0_.NAME as NAME4_1_1_, artiquleen0_.SHORT_NAME as SHORT_NA5_1_1_, artiquleen0_.STATUS_ID as STATUS_I6_1_1_ from ARTIQULE artiquleen0_ where artiquleen0_.GROUP_ID=?
Hibernate: select artiquleen0_.GROUP_ID as GROUP_ID2_1_0_, artiquleen0_.ID as ID1_1_0_, artiquleen0_.ID as ID1_1_1_, artiquleen0_.GROUP_ID as GROUP_ID2_1_1_, artiquleen0_.METRIC_ID as METRIC_I3_1_1_, artiquleen0_.NAME as NAME4_1_1_, artiquleen0_.SHORT_NAME as SHORT_NA5_1_1_, artiquleen0_.STATUS_ID as STATUS_I6_1_1_ from ARTIQULE artiquleen0_ where artiquleen0_.GROUP_ID=?
Hibernate: select artiquleen0_.GROUP_ID as GROUP_ID2_1_0_, artiquleen0_.ID as ID1_1_0_, artiquleen0_.ID as ID1_1_1_, artiquleen0_.GROUP_ID as GROUP_ID2_1_1_, artiquleen0_.METRIC_ID as METRIC_I3_1_1_, artiquleen0_.NAME as NAME4_1_1_, artiquleen0_.SHORT_NAME as SHORT_NA5_1_1_, artiquleen0_.STATUS_ID as STATUS_I6_1_1_ from ARTIQULE artiquleen0_ where artiquleen0_.GROUP_ID=?

感谢回复。

Answer 1

多个正在运行的查询可能是因为 n + 1 问题。

使用JOIN FETCH 在一个查询中获取父实体和所有映射的子实体。

查看this 类似的答案。

Answer 2

使用 hql join fetch 解决的问题， 在我的选项中选择看起来像这样

from AR_GROUP list left outer join fetch list.artiqules