Tell us about your experience designing and using abstract models, as well as working with polymorphism and instances in Django.

In Django, abstract models are used to create base model classes that do not create a separate table in the database but allow inheriting common fields and methods. This is convenient for code reuse.

Example of an abstract model:

from django.db import models

class TimestampedModel(models.Model):
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True

class Article(TimestampedModel):
    title = models.CharField(max_length=200)
    content = models.TextField()

Here, TimestampedModel is an abstract model, and its fields are inherited in Article.

Polymorphism in Django is achieved through model inheritance and method overriding. You can also use third-party libraries to support polymorphic queries.

Working with model instances involves creating, modifying, and saving objects in the database:

article = Article(title='Example', content='Article text')
article.save()

Thus, experience includes designing base abstract models for reuse, using inheritance for polymorphism, and working with model instances for CRUD operations.