java - 在 Set 中获取多个连接数据

Question

我正在尝试获取专辑详细信息以及与该专辑关联的所有图像以设置 piSet 但它并未获取所有图像以设置 piSet

我喜欢

 albumname   in al object     
     ABC 
    images in piSet
               image1
               image2
               image3  
               ....

数据获取代码是

 con = ConnectionFactory.getConnection();
                    List<Album> aList = new ArrayList<Album>();
                    try {
                        ps = con.prepareStatement("select distinct album.*,pi.* from   "
                                + "atom as a  "
                                + "left join album as album "
                                + "on   "
                                + "a.id=album.aid "
                                + "left join post_images as pi  "
                                + "on   "
                                + "album.id=pi.album_id "
                                + "where  "
                                + "a.id=? "
                                + "and a.status=? ");
                        ps.setLong(1, aid);
                        ps.setString(2, "Active");
                        rs = ps.executeQuery();

                        while (rs.next()) {
                            Set<PostImages> piSet = new HashSet<PostImages>();
                            Album al = new Album();
                            al.setId(rs.getLong("album.id"));
                            al.setName(rs.getString("album.name"));
                            PostImages pi = new PostImages();
                            pi.setImageId(rs.getLong("pi.image_id"));
                                    pi.setLargePicPath(rs.getString("pi.large_pic_path"));

                            piSet.add(pi);
                            al.setPostImageses(piSet);
                            aList.add(al);
                        }
                    } catch (SQLException e) {}

如何修改上面的代码以获取所有图像到“PiSet”。

Answer 1

假设id在album表中是唯一的，上面的代码可以满足你的要求:

rs = ps.executeQuery();
HashMap<Long, Album> AlbumMap = new HashMap<Long, Album>();
while (rs.next()) {
    Long albumId = rs.getLong("album.id");//assume album.id is unique.
    Album al = AlbumMap.get(albumId);
    if (al == null) {
        al = new Album();
        al.setId(albumId);
        al.setName(rs.getString("album.name"));
        Set<PostImages> piSet = new HashSet<PostImages>();
        al.setPostImageses(piSet);
        aList.add(al);
        AlbumMap.put(albumId, al);
    }
    PostImages pi = new PostImages();
    pi.setImageId(rs.getLong("pi.image_id"));
            pi.setLargePicPath(rs.getString("pi.large_pic_path"));
    al.getPostImageses().add(pi);
}