java - JPA Criteria API加入

请帮我一下。我已经读了大约10篇文章，但不了解加入的时刻。我有2张桌子：

public class News implements Serializable {
@Id
@GeneratedValue (generator = "increment")
@GenericGenerator (name = "increment", strategy = "increment")
private int id;
@Column
private String name;
@Column
private Date created;
@Column
private String data;
@ManyToOne (cascade = CascadeType.ALL, fetch = FetchType.LAZY)
@JoinColumn (name = "category_id")
private NewsCategoryDict category;
// getters, setters
}

和

public class NewsCategoryDict implements Serializable {
@Id
@GeneratedValue (generator = "increment")
@GenericGenerator (name = "increment", strategy = "increment")
private int id;
@Column
private String name;
@OneToMany (mappedBy = "category", cascade = CascadeType.ALL)
private List<News> news = new ArrayList<>();
}

我希望查询像

SELECT * FROM news, categorynews WHERE news.category_id = categorynews.id;

然后用

    <div id="list_news">
        <c:forEach items="${news}" var="news">
            <h5>${news.id} : ${news.name} - ${news.created} ; ${news.data} (${news.category.name})</h5>
        </c:forEach>
    </div>

而且我只是无法理解使用Criteria API进行的这种联接。你能帮助我吗 ？
尝试使用此代码段，但出现错误

public List<News> getAll() {
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<News> cq = cb.createQuery(News.class);
    Root<News> rootFromNews = cq.from(News.class);
    Join<NewsCategoryDict, News> join = rootFromNews.join("category");
    cq.select(join);

    return em.createQuery(cq).getResultList();
}

  PropertyNotFoundException：在类型ru.r1k0.spring.model.NewsCategoryDict上找不到“已创建”属性

最佳答案

假设您要返回与News实例相关联的NewsCategoryDict实例，您的条件查询应如下所示：

public List<News> getAll() {
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<News> cq = cb.createQuery(News.class);
    Root<News> rootFromNews = cq.from(News.class);
    Join<News, NewsCategoryDict> join = rootFromNews.join("category"); // #1
    cq.select(rootFromNews);  // #2

    return em.createQuery(cq).getResultList();
}

修改后的行标记有#1和#2注释。

查询应返回所有具有匹配的News的NewsCategoryDict；但是不返回与News记录无关的NewsCategoryDict记录。