0

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 + " ]";
    }

}

我想获取特定帖子的图像集合，例如 Collection objPostImage = objPost.getPostImageCollection() 但多对一关系不向我提供此功能如何将其转换为一对多或如何获取帖子的图像集合。？我是java新手，所以任何帮助和建议都将提前感谢thanx ...

4

2 回答 2

0

您可以在 Post 对象中添加一个 java.util.Set 的 PostImages，并使用 Hibernate 映射来提供关系。 这个网站有一个很好的例子来建立一对多的关系。

因此，例如，您可能希望在 Post 类中添加如下内容：

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;
}

添加后，您将能够在 Post 对象上调用 getPostImages() 方法。

于 2012-06-05T17:19:24.187 回答
0

尝试这个：

@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 的回答不起作用的原因是因为 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 提供者应如何访问此数据。

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;
    }
}

然而，当使用@Access(AccessType.PROPERTY)字段时（至少在 EclipseLink 中），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;
    }
}
于 2012-06-07T06:42:03.483 回答