What does the term ForeignKey mean in the context of databases and how is it used to link tables?

In databases, the term ForeignKey refers to a field or a set of fields in one table that references the primary key of another table. This mechanism establishes and enforces a relationship between tables, helping to maintain data integrity.

For example, if there is an Orders table with a CustomerID field that is a foreign key referencing the ID field in the Customers table, then each record in Orders is linked to a specific customer in Customers.

Using a ForeignKey allows:

• Ensuring referential integrity (you cannot add an order with a non-existent customer).
• Simplifying data joins from related tables.

In Python, for example with Django ORM, a foreign key is defined as follows:

from django.db import models

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

class Order(models.Model):
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
    order_date = models.DateField()

Here, customer is a foreign key linking the order to the customer.