Question

我是hibernate的新手，我遇到了有关映射类的问题。我有两个类Song和User

public class Song implements Serializable {
private Album album;
private String title;
private int rating;
private String artist;
private String composer;
private Genre genre;
private int songId;
//getters and setters
} 

public class user{
 private String userName;
 private String password;
 private int user_id;

//getters and setters
}

我必须使用他帐户中的歌曲映射每个用户。要做到这一点，我有一个表user_songs_mapping表，其中有song_id和user_id作为列...我没有得到如何映射这种关系我休眠

Answer 1

您应该使用多对多设置，例如注释你是＆lt; d：

class Song {
  @ManyToMany
  @JoinTable( name = "user_songs_mapping",
    joinColumns = @JoinColumn ( name = "song_id", referencedColumnName = "songid" ), //assuming the id column in the song table is named songid
    inverseJoinColumns = @JoinColumn ( name = " user_id", referencedColumnName = "userid" ) ) //assuming the id column in the user table is named userid
  Set<Users> users;
}

class User {
  @ManyToMany( mappedBy = "users" )
  Set<Song> songs;
}

请注意，一方定义表，另一方只声明在哪里找到映射。在我的示例中，Song将是拥有方，即您需要更新Song中设置的用户以保持更改。如果您希望User成为拥有者，只需切换注释并加入列。

更新：重读您的问题我假设您想要一个单向关联用户 - >歌曲。因此，只需将关系添加到User：

class User{
  @ManyToMany
  @JoinTable( name = "user_songs_mapping",
    joinColumns = @JoinColumn ( name = " user_id", referencedColumnName = "userid" ),
    inverseJoinColumns = @JoinColumn ( name = "song_id", referencedColumnName = "songid" ) )
  Set<Song> songs;
}

Answer 2

如果您使用xml将表映射到类，那么它将是这样的：

＆＃13;

<hibernate-mapping>
   <class name="User" table="user">      
	  <!-- column attribute contains the name using in data base and name attribute contains the name using in calss -->
      <id name="id" type="int" column="user_id">
         <generator class="native"/>
      </id>
      <set name="songs" cascade="save-update" table="user_songs_mapping">
         <key column="user_id"/>
         <many-to-many column="song_id" class="Song"/>
      </set>
      <property name="userName" column="user_name" type="string"/>      
      <!-- other properties-->
   </class>

   <class name="Song" table="song">	
      <id name="songId" type="int" column="song_id">	  
         <generator class="native"/>
      </id>
      <property name="title" column="title" type="string"/>
	  <!-- other properties-->		
   </class>

</hibernate-mapping>

＆＃13;

Answer 3

它是一个与连接表有多对多关系的经典案例。

两个类声明都应该在具有其他类对象的集合上具有@manyToMany注释。通过使用连接注释“here User”使一个类成为连接所有者，并将layoutby属性放在其他类“here Song”中。示例如下。

public class User{

 @Id
 @Column(name="USER_ID") 
 private int user_id;

 @Column(name="USER_NAME")
 private String userName;

 @ManyToMany(cascade = {Google this and use what you want as per your requarement})
 @JoinTable(name="USER_SONGS_MAPPING", 
                joinColumns={@JoinColumn(name="USER_ID")}, 
                inverseJoinColumns={@JoinColumn(name="SONG_ID")})
  private Set<Song> songs= new HashSet<Song>();

//getters and setters
}

public class Song {

// Other fileds

    @ManyToMany(mappedBy="songs")
    private Set<User> users = new HashSet<User>();

//getters and setters
}

有关更多信息，请使用hibernate docs http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html/ch07.html

如何在hibernate中映射两个不相关的类

3 个答案: