Add the `:environment` task as dependency for Rake task to access models.

desc "count number of users"
task :count_users do
  puts User. count # NameError: uninitialized constant User (NameError)
end

To make the models available, tell Rails to load the environment before running the task.
desc "count number of users"
task count_users: [:environment] do
  puts User. count
end