Hibernate HQL投影使用实体ManyToMany定义问题

Question

问题：当我将实体集合字段作为HQL语句的一部分引用时，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（它是定义为ManyToMany连接的集合，如下所示）。这工作正常，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)

一旦我这样做，我得到一个空集。这意味着hibernate生成的SQL查询不会返回任何内容。我已经通过在SQL管理器中执行该命令来验证这一点，该命令不返回任何结果。

这是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

也许我设置了错误的定义，或者我在这里错过了HQL的限制，我不确定。非常感谢我能得到的任何帮助。谢谢！

此致 本

Answer 1

您知道使用此查询生成笛卡尔积，对吗？

查询可以更好地显示为：

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

因为您尚未指定显式连接，所以假定INNER JOIN不是LEFT JOIN。

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，这也是您报告的内容：

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

但是当没有后果时，INNER JOIN将不会返回任何结果，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)