Challenge 3: Fix an N+1 Query — Solution

Original (N+1 problem):
Author.all.each { |author| puts author.books.count }

Total queries for 20 authors: 21
(1 query for Author.all, plus 1 additional query per author inside the
loop for author.books.count — 1 + 20 = 21 queries total.)

Fixed:
Author.includes(:books).each { |author| puts author.books.count }

New total query count: 2
(1 query for the authors themselves, plus 1 additional query that
eager-loads every author's books all at once, run BEFORE the loop starts
— regardless of how many authors exist, the total stays at 2.)

=begin
Notes:
- The original version's cost scales directly with the number of authors
  -- 200 authors would mean 201 queries, not just 21. This is exactly why
  the N+1 problem gets worse (and more noticeable) as real data grows,
  even though it looks harmless with a small test dataset.
- .includes(:books) is the one-word fix: it tells Active Record to
  eager-load the association ahead of time in a single extra query,
  instead of lazily querying for each author's books individually the
  first time author.books is actually accessed inside the loop.
- The fixed version's query count stays flat at 2 no matter how many
  authors exist, which is the actual goal -- not just "fewer queries" but
  a query count that doesn't grow with the size of the dataset.
=end