Hibernate HQL投影使用实体很多定义问题

Question

问题：当我引用实体集合字段作为HQL语句的一部分时，HQL查询没有返回任何结果。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（它是定义为多个联接的集合，如下所示）。这很好，但当我尝试引用另一个映射为多个联接的投影集合时，问题就出现了。

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

一旦我这样做，我就得到一个空的集合。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管理器中执行命令验证了这一点，该命令不返回任何结果。

以下是附带事项：

/**
 * 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;
    }

    ...
}

类别类型实体关系定义：

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

结果实体关系定义：

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

数据结构：

使用Hibernate 3.6.10

也许我设置的定义是错误的，或者我缺少HQL的一个限制，我不确定。如果我能在这里得到任何帮助，我将不胜感激。谢谢

你好，本

Answer 1

您知道您正在使用此查询生成笛卡尔积，对吗？

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)

因为没有指定显式联接，所以假定内部联接不是左联接。

让我们假设指定的事件有类别。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)

但当没有结果时，内部联接将不返回结果，因此：

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

不会返回任何内容，但您的查询也可能会出现这种情况：

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