fixed a mistake on adding the models

Neptune_Sy_music/about/models.py

 # about/models.py
 from django.db import models
 
-
 class Artist(models.Model):
+    artist_name = models.CharField(max_length=50, unique=True)
+    monthly_listeners = models.IntegerField()
     birth_name = models.CharField(max_length=50, unique=True)
-    bio = models.TextField()
+    bio = models.TextField(null=False)
     pass
 
 
 class Album(models.Model):
+    album_name = models.CharField(max_length=50, unique=True)
+    artist = models.ForeignKey(
+        Artist,
+        on_delete=models.CASCADE,
+    )
+    description = models.CharField(max_length=500, unique=True)
+    release_date = models.DateField()
     label = models.CharField(max_length=50, unique=True)
     song_count = models.IntegerField()
-    
+    pass
 
 
 class Song(models.Model):
+    song_title = models.CharField(max_length=50)
+    artist = models.ForeignKey(
+        Artist,
+        on_delete=models.CASCADE,
+        related_name='single'
+    )
+    album = models.ForeignKey(
+        Album,
+        on_delete=models.CASCADE,
+    )
+    song_length = models.TimeField()
     music_video = models.BooleanField()
     lyrics = models.TextField()
\ No newline at end of file