no_eager_load.rb

# Assuming User has the following association
class User
  has_many :posts
end

# Running this activerecord code
users = User.all

users.each do |user|
  user.posts
end

# Will generate n+1 queries, where n is the number of users, namely
# SELECT * FROM users;
# SELECT * FROM posts WHERE posts.user_id = 1;
# SELECT * FROM posts WHERE posts.user_id = 2;
# SELECT * FROM posts WHERE posts.user_id = 2;
#   .....
# SELECT * FROM posts WHERE posts.user_id = n;