How do you add database indexes in Django models, and when should you use them? Django मॉडल्स में डेटाबेस इंडेक्स कैसे जोड़ें, और इनका उपयोग कब करना चाहिए?

A database index is a separate data structure that lets the database look up rows matching a condition without scanning the entire table, dramatically speeding up queries that filter, order, or join on that column — at the cost of extra storage and slightly slower writes, since indexes must be updated on every insert/update.

In Django, an index is added by setting db_index=True on a field or, preferably for multi-column and more control, adding entries to a model's Meta.indexes list using models.Index. Indexes are most valuable on columns frequently used in filter(), order_by(), or as foreign keys (which Django indexes automatically); indexing every column indiscriminately hurts write performance without meaningful read benefit.

class Order(models.Model):
    status = models.CharField(max_length=20, db_index=True)
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
    created_at = models.DateTimeField()

    class Meta:
        indexes = [
            models.Index(fields=['status', 'created_at']),
        ]