Hibernate HQL 投影使用实体多对多定义问题

Question

问题：当我引用实体集合字段作为 HQL 语句的一部分时，HQL 查询未返回任何结果。它适用于一个 HQL 投影，例如：

select inc.categoryTypes as categoryTypes from IncidentEntity inc where (inc.id = :id105019)

categoryTypes 是 IncidentEntity 类字段之一（它是一个定义为 ManyToMany 连接的集合，如下所示）。这很好用，但是当我尝试引用另一个映射为 ManyToMany 连接的投影集合时会出现问题。

select inc.categoryTypes as categoryTypes, inc.consequences as consequences from IncidentEntity inc where (inc.id = :id105019)

只要我这样做，我就会得到一个空集。这意味着休眠生成的 SQL 查询没有返回任何内容。我已通过在 SQL 管理器中执行不返回任何结果的命令来验证这一点。

这里是 IncidentEntity：

/**
 * Database entity for the 'incidents' table records.<br>
 * Entity domain object is {@link nz.co.doltech.ims.shared.domains.Incident}
 * @author Ben Dol
 * 
 */
@javax.persistence.Entity(name = "incidents")
@Cache(usage=CacheConcurrencyStrategy.TRANSACTIONAL)
public class IncidentEntity implements Entity {

    ...

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "incident_categorytype", joinColumns = { 
            @JoinColumn(name = "incident_id") }, 
        inverseJoinColumns = {
            @JoinColumn(name = "categorytype_id") 
    })
    private Set<CategoryTypeEntity> categoryTypes = new HashSet<CategoryTypeEntity>();

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "incident_consequence", joinColumns = { 
            @JoinColumn(name = "incident_id") }, 
        inverseJoinColumns = {
            @JoinColumn(name = "consequence_id") 
    })
    private Set<ConsequenceEntity> consequences = new HashSet<ConsequenceEntity>();

    ...

    public Set<CategoryTypeEntity> getCategoryTypes() {
        return categoryTypes;
    }
    public void setCategoryTypes(Set<CategoryTypeEntity> categoryTypes) {
        this.categoryTypes = categoryTypes;
    }

    public Set<ConsequenceEntity> getConsequences() {
        return consequences;
    }
    public void setConsequences(Set<ConsequenceEntity> consequences) {
        this.consequences = consequences;
    }

    ...
}

CategoryTypeEntity 关系定义：

@ManyToMany(fetch = FetchType.LAZY, mappedBy = "categoryTypes")
private Set<IncidentEntity> incidents = new HashSet<IncidentEntity>();

ConsequenceEntity 关系定义：

@ManyToMany(fetch = FetchType.LAZY, mappedBy = "consequences")
private Set<IncidentEntity> incidents = new HashSet<IncidentEntity>();

数据结构：

使用 Hibernate 3.6.10

也许我的定义设置错误，或者我在这里缺少 HQL 的限制，我不确定。将不胜感激我能在这里得到的任何帮助。谢谢！

问候， 本

Answer 1

您知道您正在使用此查询生成笛卡尔积，对吧？

查询可以更好地可视化为：

select categoryTypes, consequences 
from IncidentEntity inc 
inner join inc.categoryTypes as categoryTypes
inner join inc.consequences as consequences
where (inc.id = :id105019)

由于您没有指定显式联接，因此假定 INNER JOIN 不是 LEFT JOIN。

让我们假设指定事件有类别。因此，此查询将返回此事件的类别，这也是您报告的：

select categoryTypes
from IncidentEntity inc 
inner join inc.categoryTypes as categoryTypes
where (inc.id = :id105019)

但是当没有结果时，INNER JOIN 将不返回任何结果，所以：

select categoryTypes, consequences 
from IncidentEntity inc 
inner join inc.consequences as consequences
where (inc.id = :id105019)

不会返回任何内容，但您的查询也会发生这种情况：

select categoryTypes, consequences 
from IncidentEntity inc 
inner join inc.categoryTypes as categoryTypes
inner join inc.consequences as consequences
where (inc.id = :id105019)