diff --git a/src/main/java/com/vibevault/model/Song.java b/src/main/java/com/vibevault/model/Song.java
index 953c654..ec3f168 100644
--- a/src/main/java/com/vibevault/model/Song.java
+++ b/src/main/java/com/vibevault/model/Song.java
@@ -4,14 +4,18 @@ import jakarta.persistence.*;
 
 /**
  * 歌曲实体类
- * 
- * 需要实现：
+ *
+ * 需要实现:
  * - 将此类映射为数据库表 "songs"
  * - id 作为自增主键
  * - 每首歌曲属于一个歌单（多对一关系）
  */
+@Entity // 实现：将此类映射为数据库表
+@Table(name = "songs") // 实现：指定表名为"songs"
 public class Song {
 
+    @Id // 实现：标记id为主键
+    @GeneratedValue(strategy = GenerationType.IDENTITY) // 实现：id作为自增主键
     private Long id;
 
     private String title;
@@ -20,33 +24,63 @@ public class Song {
 
     private int durationInSeconds;
 
+    // 实现：每首歌曲属于一个歌单（多对一关系）
+    @ManyToOne(fetch = FetchType.LAZY, optional = false) // 多对一，歌单不能为空
+    @JoinColumn(name = "playlist_id") // 数据库中关联歌单的字段名
     private Playlist playlist;
 
+    // JPA必须的无参构造（protected改为public，方便测试）
     public Song() {
     }
 
+    // 适配测试代码的构造方法（不带Playlist参数）
     public Song(String title, String artist, int durationInSeconds) {
         this.title = title;
         this.artist = artist;
         this.durationInSeconds = durationInSeconds;
     }
 
+    // 业务用的构造方法（带Playlist参数）
+    public Song(String title, String artist, int durationInSeconds, Playlist playlist) {
+        this.title = title;
+        this.artist = artist;
+        this.durationInSeconds = durationInSeconds;
+        this.playlist = playlist;
+    }
+
+    // 必要的getter/setter方法
     public Long getId() {
         return id;
     }
 
+    public void setId(Long id) {
+        this.id = id;
+    }
+
     public String getTitle() {
         return title;
     }
 
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
     public String getArtist() {
         return artist;
     }
 
+    public void setArtist(String artist) {
+        this.artist = artist;
+    }
+
     public int getDurationInSeconds() {
         return durationInSeconds;
     }
 
+    public void setDurationInSeconds(int durationInSeconds) {
+        this.durationInSeconds = durationInSeconds;
+    }
+
     public Playlist getPlaylist() {
         return playlist;
     }
@@ -54,4 +88,4 @@ public class Song {
     public void setPlaylist(Playlist playlist) {
         this.playlist = playlist;
     }
-}
+}
\ No newline at end of file