ai_api/models.py [chapter] deterministic

from django.db import models class ChatSession(models.Model): id = models.UUIDField(primary_key=True, default=uuid.uuid4) created_at = models.DateTimeField(auto_now_add=True) updated_at = models.DateTimeField(auto_now=True) title = models.CharField(max_length=255) class ChatMessage(models.Model): session = models.ForeignKey(ChatSession, related_name='messages', on_delete=models.CASCADE) role = models.CharField(max_length=10, choices=[('', 'User'), ('', 'Assistant')]) content = models.TextField() created_at = models.DateTimeField(auto_now_add=True)

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Create serializers to validate input and serialize responses.

```python