Django Rest Framework writable nested field using create()

Question

I'm trying to write a create method that will write my nested fields but am finding that the nested object isn't written.

This is the sample I was using:

class UserSerializer(serializers.ModelSerializer):
 profile = ProfileSerializer()
 class Meta:
 model = User
 fields = ('username', 'email', 'profile')
 def create(self, validated_data):
 profile_data = validated_data.pop('profile')
 user = User.objects.create(**validated_data)
 Profile.objects.create(user=user, **profile_data)
 return user

But I'm failing to understand what the user=user refers to.

Here is my code:

class MessagesSerializer(serializers.HyperlinkedModelSerializer):
 id = serializers.IntegerField(source='pk', read_only=True)
 suggested_songs = SongSerializer()
 class Meta:
 model = Messages
 fields = ('id','owner','url','suggested_songs',)
 #fields = ('id','url','suggested_songs',)
 def create(self, validated_data):
 song_data = validated_data.pop('suggested_songs')
 message = Messages.objects.create(**validated_data)
 Song.objects.create(**song_data)
 return message
class SongSerializer(serializers.HyperlinkedModelSerializer):
 #id = serializers.IntegerField(source='pk', read_only=True)
 class Meta:
 model = Song
 fields = ('id','title','artist','album','albumId','num_votes','cleared')
 read_only_fields = ('song_id')
class Messages(models.Model):
 owner = models.OneToOneField(User, primary_key=True, related_name='user_messages', editable=False) #TODO, change owner to 'To'
 #suggested_songs = models.ManyToManyField(Song, related_name='suggested_songs')
 suggested_songs = models.ForeignKey(Song, null=True, blank=True)
 # If a user is added, this runs. 
 @receiver(post_save, sender=User)
 def create_friend_for_user(sender, instance=None, created=False, **kwargs):
 if created:
 Messages.objects.get_or_create(owner=instance)
 # Same as above, but for deletion 
 @receiver(pre_delete, sender=User)
 def delete_friend_for_user(sender, instance=None, **kwargs):
 if instance:
 Messages.objects.get(owner=instance).delete()
class Song(models.Model):
 """
 A model which holds information about the songs.
 """
 #song_id = models.IntegerField(primary_key=True)
 title = models.CharField(max_length=150, blank=True, default='')
 artist = models.CharField(max_length=150, blank=True, default='')
 album = models.CharField(max_length=150, blank=True, default='')
 albumId = models.CharField(max_length=150, blank=True, default='')
 num_votes = models.IntegerField(default=0, blank=True)
 cleared = models.BooleanField(default=False, blank=True)
 class Meta:
 ordering = ('title',)
 #managed=True

• qwattash: You mean that the Song and Messages objects are created but not linked together or the Song is not created at all?

Answer 1

I think that the issue might be in the MessageSerializer.create method:

def create(self, validated_data):
 # here you are popping the suggested songs
 song_data = validated_data.pop('suggested_songs')
 # so when you create the message here the foreign key is set to NULL
 message = Messages.objects.create(**validated_data)
 # and here you create the Song instance correctly but it is not
 # associated with the message
 Song.objects.create(**song_data)
 return message

You need to pass the foreign key to the Messages.create method like in the example you have.

def create(self, validated_data):
 song_data = validated_data.pop('suggested_songs')
 song = Song.objects.create(**song_data)
 # song need to be created first because the foreign key is in
 # the Messages model
 message = Messages.objects.create(suggested_songs=song, **validated_data)
 return message

I hope this helps!