has_many/belongs_to relationships & query questions - ruby-on-rails

Question

I am building an attendance tracker right now. I have three models currently. I am using devise for my User model
class User < ActiveRecord::Base
has_many :clients
has_many :attendances
class Client < ActiveRecord::Base
belongs_to :user
has_many :attendances
class Attendance < ActiveRecord::Base
belongs_to :user
belongs_to :client
The columns on the attendance table are user_id client_id created_at and updated_at
Here's my thought process:
I can get all of the attendances for each User
I can also get all of the attendances for a specific Client
I can get all of the attendance records for a specific User and Client by way of: Attendance.joins(:user, :client).where(:user_id => current_user) which returns an
<ActiveRecord::Relation [#<Attendance id: 18, client_id: 151, created_at: "2015-07-24 21:36:16", updated_at: "2015-07-24 21:36:16", user_id: 4>, #<Attendance id: 19, client_id: 101, created_at: "2015-07-24 21:37:10", updated_at: "2015-07-24 21:37:10", user_id: 4>, #<Attendance id: 20, client_id: 114, created_at: "2015-07-24 21:37:39", updated_at: "2015-07-24 21:37:39", user_id: 4>, #<Attendance id: 21, client_id: 123, created_at: "2015-07-24 21:38:26", updated_at: "2015-07-24 21:38:26", user_id: 4>]>
Can I somehow refer back to Client table to get information like first_name or email with another where, include, or joins statement?
Or am I missing something altogether and maybe need a join table and do a has_many, through: relationship?

Answer 1

Brad's comment above is technically correct, but since the .joins clause on your query only includes those tables for the execution of the actual query, the data from the Users and Clients tables isn't actually going to get loaded in by Rails, so in order to fetch all their data you'll end up executing N+1 queries (a common cause of slow Rails apps!). That is:
irb> User.joins(:groups).each { |u| u.groups.map(&:name) }
User Load (8.6ms) SELECT "users".* FROM "users" INNER JOIN "groups" ON "groups"."user_id" = "users"."id"
Group Load (1.2ms) SELECT "groups".* FROM "groups" WHERE "groups"."user_id" = $1 [["user_id", 1]]
Group Load (0.6ms) SELECT "groups".* FROM "groups" WHERE "groups"."user_id" = $1 [["user_id", 1]]
Group Load (0.7ms) SELECT "groups".* FROM "groups" WHERE "groups"."user_id" = $1 [["user_id", 1]]
Group Load (0.7ms) SELECT "groups".* FROM "groups" WHERE "groups"."user_id" = $1 [["user_id", 2]]
Group Load (0.6ms) SELECT "groups".* FROM "groups" WHERE "groups"."user_id" = $1 [["user_id", 3]]
Not so bad now, but imagine if you had a thousand users! We can fix this, though. If you use the .includes method, you'll both join onto the other table(s) and load their data into memory. It still runs 2 queries, but that's an improvement:
irb(main):016:0> User.includes(:groups).each { |u| u.groups.map(&:name) }
User Load (0.6ms) SELECT "users".* FROM "users"
Group Load (1.2ms) SELECT "groups".* FROM "groups" WHERE "groups"."user_id" IN (1, 2, 3, 4)
So, for your case, try this instead:
Attendance.includes(:user, :client).where(user_id: current_user)
For more info on the difference between includes and joins, see this blog post, or Google "rails joins vs includes".