Can you explain what the N+1 problem is in ORM and why it occurs?

The N+1 problem occurs when working with ORM, where one query is executed for the main entity and an additional N queries are executed — one for each related record.

For example, if you need to get a list of users and their addresses, ORM might first query all users (1 query), and then for each user, query the address separately (N queries). This leads to a large number of queries and reduces performance.

To avoid the N+1 problem, techniques like eager loading are used, for example, with select_related or prefetch_related in Django ORM, which allow fetching all necessary data with a minimal number of queries.