mysql - Fetch 仅返回集合中的一项

Question

表格信息:

Image 表包含其父表 Media 的外键 mediaid

----------
id  | mediaid | url
========================
104 | 103     | IMG_PATH
383 | 103     | IMG_PATH
384 | 103     | IMG_PATH
395 | 103     | img_path

Media 实体拥有图像集合:

private Set<Image> images  = new HashSet<Image>(0)`;

@OneToMany(mappedBy = "media", targetEntity = Image.class ,cascade = CascadeType.ALL)
public Set<Image> getImages() {
   return images;
}

---

图片实体片段:

private Media media;
@ManyToOne
@JoinColumn(name = "mediaId")
public Media getMedia() {
    return media;
}

---

我实现了以下查询，它应该返回一个 Media 对象，其中包含所有图像的集合，其 fk 与其提供的 id 匹配。

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Media> cqObject = cb.createQuery(Media.class);
Root<Media> rootEntry = cqObject.from(Media.class);

rootEntry.fetch(Media_.images, JoinType.LEFT);              
Predicate predicate = cb.equal(rootEntry.get(Media_.id), id);           
cqObject.select(rootEntry).where(predicate);        
Media _fetcheMedia = em.createQuery(cqObject).getSingleResult();

返回的媒体对象集合只包含一个图像项。我确定数据库包含指定媒体的多个图像项。

*注意Media_只是一个表示媒体实体的元模型类

hibernate id=103 的媒体对象

select media0_.mediaId as mediaId1_8_0_, 
    images1_.imageId as imageId1_6_1_, 
    media0_.active as active2_8_0_, 
    media0_.created as created3_8_0_, 
    media0_.description as descript4_8_0_,
    media0_.listType as listType5_8_0_, 
    media0_.parentId as parentId6_8_0_, 
    media0_.propertyTypeId as property7_8_0_, 
    media0_.seasonId as seasonId8_8_0_, 
    media0_.status as status9_8_0_, 
    media0_.userId as userId10_8_0_, 
    images1_.active as active2_6_1_, 
    images1_.created as created3_6_1_, 
    images1_.imageTypeId as imageTyp5_6_1_, 
    images1_.imageUrl as imageUrl4_6_1_, 
    images1_.mediaId as mediaId6_6_1_, 
    images1_.mediaId as mediaId6_6_0__, 
    images1_.imageId as imageId1_6_0__ from media media0_ 
    left outer join image images1_ on media0_.mediaId=images1_.mediaId where media0_.mediaId=103

Answer 1

这对我来说是一个愚蠢的错误，我忘记覆盖 Image 实体的 hashcode 和 equals 方法。添加了它们，它知道它应该正常工作。

@Override
    public int hashCode() {
        final int prime = 31;
        int result = super.hashCode();
        result = prime * result + (int) (id ^ (id >>> 32));
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (!super.equals(obj))
            return false;
        if (getClass() != obj.getClass())
            return false;
        Image other = (Image) obj;
        if (id != other.id)
            return false;
        return true;
    }