java - Hibernate 加载一一不需要的标记为延迟获取类型的实体

Question

通过hibernate使用postgresql数据库。我有一个实体(表)TeamInfo(bb_team_info)并尝试执行以下代码:

strQuery.append("SELECT * from bb_team_info WHERE id in (SELECT bb_team_info_id FROM bb_team_league_info tl WHERE tl.bb_league_id = :leagueID)");
    Query query2 = em.createNativeQuery(strQuery.toString(), TeamInfo.class);
    query2.setParameter("leagueID", leagueID.getId());
    List<TeamInfo> myteaminfolist = query2.getResultList();

这是 TeamInfo 类:

@Entity
@Table(name="bb_team_info")
@BatchSize(size=50)
public class TeamInfo implements Serializable {
private Integer id;
... some fields here ...
private TeamFinance finance;
private Manager manager;

public TeamInfo() {
}

....

@OneToOne (mappedBy="teamInfo", fetch=FetchType.LAZY)
public Manager getManager() {
    return manager;
}
...


@OneToOne(targetEntity=TeamFinance.class, fetch=FetchType.LAZY, mappedBy="teamInfo", cascade=CascadeType.ALL)
public TeamFinance getFinance() {
    return finance;
}

}

发出的实际请求(从 postgresql 日志中看到):

SELECT * from bb_team_info WHERE id in (SELECT bb_team_info_id FROM bb_team_league_info tl WHERE tl.bb_league_id = $1)

这正是预期的结果，但后来我看到很多这样的查询:

select ... from bb_team_finances teamfinanc0_ where teamfinanc0_.bb_team_info_id=$1...
select ... from bb_manager where manager0_.bb_team_info_id=$1...
select ... from bb_team_finances teamfinanc0_ where teamfinanc0_.bb_team_info_id=$1...
select ... from bb_manager where manager0_.bb_team_info_id=$1...

如果获取类型设置为惰性，为什么 hibernate 会选择这些表？为什么它至少不会在两个查询中执行此操作(首先选择所有经理，然后选择财务)？

Answer 1

如果实体不“拥有”它们，Hibernate 必须急切地获取实体的 OneToOne 关系。这是因为它需要知道是否对关系或代理/实体使用 null。

要在两个查询中进行加载，您需要不同的获取策略。使用@Fetch(FetchMode.SUBSELECT)。以下是一些很好的示例:https://www.mkyong.com/hibernate/hibernate-fetching-strategies-examples/