Fields and relationships

Beyond strings and numbers, Django models express relationships—foreign keys, one-to-one, and many-to-many—keeping relational data normalized.

Common field types

• CharField, TextField, EmailField, URLField
• IntegerField, DecimalField, BooleanField
• DateField, DateTimeField, JSONField
• FileField, ImageField — uploads to MEDIA_ROOT

Relationships

class Author(models.Model):
    name = models.CharField(max_length=100)

class Article(models.Model):
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    tags = models.ManyToManyField("Tag")

on_delete defines behavior when the related row is deleted—CASCADE removes articles; PROTECT blocks deletion.

Important interview questions and answers

1. Q: ForeignKey vs ManyToMany?
   A: FK is many-to-one (many articles, one author); M2M is many-to-many (articles and tags).
2. Q: on_delete=CASCADE risk?
   A: Deleting an author deletes all their articles—sometimes PROTECT or SET_NULL is safer.
3. Q: Related name?
   A: author.articles_set or custom related_name="articles" for reverse queries.

Self-check

1. Which relationship links Article to Author?
2. What does on_delete control?