Model Relationships

Overview

Django simplifies the establishment of relationships between models, enabling the creation of a well-connected and organized database. This documentation provides insights into defining and leveraging model relationships.


Type 1 : One-to-One Relationship

Every record in one model is linked to exactly one record in another model in a one-to-one relationship.

Example :

class Pet(models.Model) :
    name = models.CharField(max_length=50)
    species = models.CharField(max_length=50)


class PetMedicalRecord(models.Model) :
    pet = models.OneToOneField(Pet, on_delete=models.CASCADE)
    vaccination_status = models.BooleanField(default=False)
    last_checkup_date = models.DateField()

In this scenario, each pet has a unique medical record captured in the PetMedicalRecord model, forming a one-to-one relationship.

Type 2 : One-to-Many Relationship

Each record in one model can be related to several records in another, whereas each record in the second model is connected to a single record in the first, according to a one-to-many relationship.

Example :

class Manufacturer(models.Model):
    name = models.CharField(max_length=100)
    location = models.CharField(max_length=150)


class Product(models.Model):
    manufacturer = models.ForeignKey(Manufacturer, on_delete=models.CASCADE)
    product_name = models.CharField(max_length=200)
    price = models.DecimalField(max_digits=8, decimal_places=2)

In this example, a manufacturer can produce multiple products, but each product is associated with only one manufacturer.

Type 3 : Many-to-Many Relationship

A many-to-many relationship implies that each record in one model can be linked with multiple records in another model.

Example :

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


class Classroom(models.Model):
    teachers = models.ManyToManyField(Teacher)
    room_number = models.CharField(max_length=10)

In this scenario, a teacher can be assigned to multiple classrooms, and a classroom can have multiple teachers.

Navigating Relationships

Once relationships are established, you can traverse them using querysets. For instance, to retrieve all books by a specific author :

author = Author.objects.get(name='J.K. Rowling')
books_by_author = author.book_set.all()

Conclusion

Building a robust and networked database in Django requires an understanding of and efficient use of model relationships. Select a relationship type that improves the overall cohesiveness of your application and fits in with your data structure.