Nested serializer does not inherit overridden to_representation - django-rest-framework

Question

I want to customise the output of serializer to group some fields of the models into a nested dictionary, so I override to_representation:
My models.py
class Snippet(models.Model):
created = models.DateTimeField(auto_now_add=True)
title = models.CharField(max_length=100, blank=True, default='')
code = models.TextField()
linenos = models.BooleanField(default=False)
language = models.CharField(choices=LANGUAGE_CHOICES, default='python', max_length=100)
style = models.CharField(choices=STYLE_CHOICES, default='friendly', max_length=100)
owner = models.ForeignKey('auth.User', related_name='snippets', on_delete=models.CASCADE)
class Meta:
ordering = ['created']
My serializers.py
class SnippetSerializer(serializers.ModelSerializer):
owner = serializers.ReadOnlyField(source='owner.username')
class Meta:
model = Snippet
fields = ['id', 'title', 'code', 'linenos', 'language', 'style', 'owner']
def to_representation(self, instance):
return {
'id': instance.id,
'owner': instance.owner.username,
'therest': {
'title': instance.title,
'code': instance.code,
'linenos': instance.linenos,
'language': instance.language,
'style': instance.style
}
}
class UserSerializer(serializers.ModelSerializer):
snippets = SnippetSerializer
class Meta:
model = User
fields = ['id', 'username', 'snippets']
depth = 1
My expected outcome of users serializer is:
[
{
"id": 1,
"username": "admin",
"snippets": [
{
"id": 1,
"owner": "admin",
"therest": {
"title": "",
"code": "foo=\"bar\"\\n",
"linenos": false,
"language": "python",
"style": "abap"
}
}
]
}
]
but I got this instead:
[
{
"id": 1,
"username": "admin",
"snippets": [
{
"id": 1,
"created": "2022-09-01T17:11:59.743112Z",
"title": "",
"code": "foo=\"bar\"\\n",
"linenos": false,
"language": "python",
"style": "abap",
"owner": 1
},
]
}
]
Nested snippets in UserSerializer does not inherit to_representation from SnippetSerializer. Did I miss something?