How to simplify my Active Record code (I want to filter has_many using join table column)? - sql

Question

This is my schema
create_table "duties", force: :cascade do |t|
t.string "name"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.boolean "is_general", default: false
t.boolean "write_all", default: true
end
create_table "duties_users", force: :cascade do |t|
t.bigint "duty_id"
t.bigint "user_id"
t.boolean "has_write_access", default: true
t.index ["duty_id"], name: "index_duties_users_on_duty_id"
t.index ["user_id"], name: "index_duties_users_on_user_id"
end
create_table "users", force: :cascade do |t|
t.string "mail"
t.text "password_digest"
t.datetime "birth_date"
t.boolean "is_admin", default: false
t.integer "rating", default: 0
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.string "name", default: ""
t.string "surname", default: ""
t.string "patronymic", default: ""
t.datetime "restore_date", default: "2021-02-11 09:57:14"
t.boolean "is_boss", default: false
end
My join model
class DutyUser < ApplicationRecord
self.table_name = "duties_users"
belongs_to :user
belongs_to :duty
end
User model
class User < ApplicationRecord
has_secure_password
has_many :duties_users, class_name: "DutyUser"
has_many :duties, through: :duties_users, class_name: "Duty"
end
And duty model
class Duty < ApplicationRecord
has_many :duties_users, class_name: "DutyUser"
has_many :users, through: :duties_users, class_name: "User"
end
I want to find all users who have write acces to a specific duty. In order to achive it i need to use something like this:
Duty.first.duties_users.find_all{|m| m.has_write_access}.map{|m| m.user}
How can i simplify this line of code?

Answer 1

The key points here are:
Duty has_many users. So if you have a duty, you can always do duty.users and that will give you the users in what's known as an "ActiveRecord Relation"
ActiveRecord Relations act a lot like arrays, except that they only give you access to instances of one model (in this case, duty.users will return a relation full of User instances) which allow you to run further queries, as well as any class methods on User. Note that unlike an array, a Relation doesn't actually contain anything. It quietly builds some SQL, and only sends that SQL to the database when you force it to (e.g. by iterating over it with .each, or asking for a .count)
Queries can be done using the where method - e.g. .where(has_write_access: true) - this is done in the database, so it's super quick.