Question

我有一个表Post和Post_Image

 @Entity
@Table(name = "post")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "Post.findAll", query = "SELECT p FROM Post p"),
    @NamedQuery(name = "Post.findByPostId", query = "SELECT p FROM Post p WHERE p.postId = :postId"),
    @NamedQuery(name = "Post.findByTitle", query = "SELECT p FROM Post p WHERE p.title = :title"),
    @NamedQuery(name = "Post.findByCreatedDatetime", query = "SELECT p FROM Post p WHERE p.createdDatetime = :createdDatetime")})
public class Post implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @NotNull
    @Column(name = "post_id")
    private Integer postId;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 500)
    @Column(name = "title")
    private String title;
    @Basic(optional = false)
    @NotNull
    @Lob
    @Size(min = 1, max = 65535)
    @Column(name = "content")
    private String content;
    @Column(name = "created_datetime")
    @Temporal(TemporalType.TIMESTAMP)
    private Date createdDatetime;
    @JoinColumn(name = "user_id", referencedColumnName = "user_id")
    @ManyToOne(optional = false)
    private User userId;
    @JoinColumn(name = "post_type_id", referencedColumnName = "post_type_id")
    @ManyToOne(optional = false)
    private PostType postTypeId;

    public Post() {
        Date date = new Date();
        this.createdDatetime =new Date(date.getTime());

    }

    public Post(Integer postId) {
        this.postId = postId;
    }

    public Post(Integer postId, String title, String content) {
        this.postId = postId;
        this.title = title;
        this.content = content;
    }

    public Integer getPostId() {
        return postId;
    }

    public void setPostId(Integer postId) {
        this.postId = postId;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public Date getCreatedDatetime() {
        return createdDatetime;
    }

    public void setCreatedDatetime(Date createdDatetime) {
        this.createdDatetime = createdDatetime;
    }

    public User getUserId() {
        return userId;
    }

    public void setUserId(User userId) {
        this.userId = userId;
    }

    public PostType getPostTypeId() {
        return postTypeId;
    }

    public void setPostTypeId(PostType postTypeId) {
        this.postTypeId = postTypeId;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (postId != null ? postId.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Post)) {
            return false;
        }
        Post other = (Post) object;
        if ((this.postId == null && other.postId != null) || (this.postId != null && !this.postId.equals(other.postId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "entity.Post[ postId=" + postId + " ]";
    }

}

和

@Entity
@Table(name = "post_image")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "PostImage.findAll", query = "SELECT p FROM PostImage p"),
    @NamedQuery(name = "PostImage.findByPostImageId", query = "SELECT p FROM PostImage p WHERE p.postImageId = :postImageId"),
    @NamedQuery(name = "PostImage.findByPath", query = "SELECT p FROM PostImage p WHERE p.path = :path"),
    @NamedQuery(name = "PostImage.findByTitle", query = "SELECT p FROM PostImage p WHERE p.title = :title")})
public class PostImage implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @NotNull
    @Column(name = "post_image_id")
    private Integer postImageId;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 500)
    @Column(name = "path")
    private String path;
    @Basic(optional = false)
    @NotNull
    @Size(min = 1, max = 500)
    @Column(name = "title")
    private String title;
    @JoinColumn(name = "post_id", referencedColumnName = "post_id")
    @ManyToOne(optional = false)
    private Post postId;

    public PostImage() {
    }

    public PostImage(Integer postImageId) {
        this.postImageId = postImageId;
    }

    public PostImage(Integer postImageId, String path, String title) {
        this.postImageId = postImageId;
        this.path = path;
        this.title = title;
    }

    public Integer getPostImageId() {
        return postImageId;
    }

    public void setPostImageId(Integer postImageId) {
        this.postImageId = postImageId;
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Post getPostId() {
        return postId;
    }

    public void setPostId(Post postId) {
        this.postId = postId;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (postImageId != null ? postImageId.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof PostImage)) {
            return false;
        }
        PostImage other = (PostImage) object;
        if ((this.postImageId == null && other.postImageId != null) || (this.postImageId != null && !this.postImageId.equals(other.postImageId))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "entity.PostImage[ postImageId=" + postImageId + " ]";
    }

}

我希望获得特定帖子的图像集合集合objPostImage = objPost.getPostImageCollection（）但很多人的关系不提供这个功能给我如何将它转换为一个或多个或如何获得一个帖子的图像集合。我是java新手，所以任何帮助和建议将不胜感激提前谢谢...

Answer 1

您可以在Post对象中添加PostImages的java.util.Set，并使用Hibernate映射来提供关系。 This site有一个很好的例子，可以建立一对多关系。

因此，例如，您可能希望在Post类中添加以下内容：

private Set<PostImage> postImages = new HashSet<PostImage>();

@OneToMany(fetch = FetchType.LAZY, mappedBy = "post")
public Set<PostImage> getPostImages() {
return this.postImages;
}

public void setPostImages(Set<PostImage> postImages) {
this.postImages= postImages;
}

然后，在PostImage类中，添加对Post对象的引用：

private Post post;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "POST_ID", nullable = false)
public Stock getPost() {
return this.post;
}

public void setPost(Post post) {
this.post= post;
}

添加之后，您将能够在Post对象上调用getPostImages（）方法。

Answer 2

试试这个：

@Entity
@Table(name = "post")
public class Post
{
    //....

    @OneToMany(mappedBy = "post")
    private Set<PostImage> images;

    //....
}

@Entity
@Table(name = "post_image")
public class PostImage
{
    //....

    @JoinColumn(name = "post_id", referencedColumnName = "id")
    @ManyToOne(optional = false)
    private Post post;

    //....
}

Seth的答案不起作用的原因是EclipseLink使用字段来访问持久性数据。（Hibernate使用属性IIRC。）您可以为每个类指定JPA提供程序应如何访问此数据。

使用字段：

@Entity
@Access(AccessType.FIELD)
public class SomeEntity
{
    @Id
    private Long id;

    //....
}

使用属性：

@Entity
@Access(AccessType.PROPERTY)
public class SomeEntity
{
    private Long id;

    //....

    @Id
    public Long getId()
    {
        return id;
    }
}

但是当使用@Access(AccessType.PROPERTY)字段时也会使用（至少在EclipseLink中），所以这样的事情是可能的：

@Entity
@Access(AccessType.PROPERTY)
public class SomeEntity
{
    private Long id;

    @Column(name = "text")
    private String someText;

    //....

    @Id
    public Long getId()
    {
        return id;
    }
}

JPA - 从ManyToOne关系中获取集合

2 个答案: