Associations for statistics - ruby-on-rails

Question

I'm new to RoR and I need some help with associations. I'm using rails 6.0.3.4 and ruby 2.7.0.
Users can create cases and cases belongs to a certain district. Districts belongs to a state. It has to be that way, because cases can't belongs to a state.
Now I want to show the number of cases for a certain diagnosis for each state. I have to use district, to get all the cases for a state. How should I build the where(...) condition?
<!-- State -->
<div class="card">
<div class="card-body">
<h5 class="card-title">State</h5>
<p><%= State.find(1).titel%> (<%= #diagnosis.cases.where(...).count %>)</p>
</div>
</div>
My Models
case.rb
class Case < ApplicationRecord
before_create :set_pseud
belongs_to :user
belongs_to :diagnosis
belongs_to :district
belongs_to :report, optional: true
end
district.rb
class District < ApplicationRecord
has_many :users
has_many :cases
has_many :reports
belongs_to :state
end
state.rb
class State < ApplicationRecord
has_many :districts
has_many :users
end
For better understanding my schema.rb:
ActiveRecord::Schema.define(version: 2021_02_11_140244) do
create_table "cases", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
t.string "first_name"
t.string "last_name"
t.string "gender"
t.date "birthdate"
t.string "place_of_residence"
t.string "diagnosis"
t.bigint "user_id"
t.datetime "confirmed_at"
t.datetime "created_at", precision: 6
t.datetime "updated_at", precision: 6, null: false
t.bigint "diagnosis_id"
t.bigint "district_id"
t.bigint "report_id"
t.string "pseud"
t.index ["diagnosis_id"], name: "index_cases_on_diagnosis_id"
t.index ["district_id"], name: "index_cases_on_district_id"
t.index ["pseud"], name: "index_cases_on_pseud"
t.index ["report_id"], name: "index_cases_on_report_id"
t.index ["user_id"], name: "index_cases_on_user_id"
end
create_table "diagnoses", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
t.string "illness"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
end
create_table "districts", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
t.string "name"
t.string "place"
t.integer "postal_code"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.bigint "state_id", null: false
t.index ["state_id"], name: "index_districts_on_state_id"
end
create_table "reports", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
t.bigint "district_id"
t.text "comment"
t.datetime "date"
t.bigint "user_id"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.index ["district_id"], name: "index_reports_on_district_id"
t.index ["user_id"], name: "index_reports_on_user_id"
end
create_table "states", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
t.string "titel"
t.string "abbr"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
end
create_table "users", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.datetime "created_at", precision: 6, null: false
t.datetime "updated_at", precision: 6, null: false
t.integer "role"
t.string "first_name"
t.string "last_name"
t.bigint "district_id"
t.bigint "state_id"
t.index ["district_id"], name: "index_users_on_district_id"
t.index ["email"], name: "index_users_on_email", unique: true
t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
t.index ["state_id"], name: "index_users_on_state_id"
end
end

Answer 1

You should add a further association into state:
has_many :cases, through: :districts
Rather than finding your state in the view, you should do that in the controller and pass it to the view in an instance variable:
#state = State.find(params[:id])
I've assumed you're using a show action here rather than manually coding the state ID for some reason.
You can then do something like this:
#state.cases.where(diagnoses: { id: #diagnosis.id }).count
Or if you prefer, you can skip the .id on #diagnosis:
#state.cases.where(diagnoses: { id: #diagnosis }).count