Using named scopes in Ruby on Rails 4 on associated models

Question

My app consists of 3 models:

FashionModel
Measurement
ModelProfile

class FashionModel < ActiveRecord::Base
  has_secure_password
  has_one :model_profile
  has_one :measurement
  accepts_nested_attributes_for :model_profile
  accepts_nested_attributes_for :measurement
end


class ModelProfile < ActiveRecord::Base
  belongs_to :fashion_model
end


class Measurement < ActiveRecord::Base
  belongs_to :fashion_model
end

The schema is roughly as follows:

create_table "fashion_models", force: :cascade do |t|
    t.string   "first_name",             limit: 25
    t.string   "last_name",              limit: 25
    t.string   "email",                  limit: 255, null: false
    t.datetime "created_at",                         null: false
    t.datetime "updated_at",                         null: false
    t.string   "password_digest",        limit: 255
    t.string   "password_reset_token",   limit: 255
    t.datetime "password_reset_sent_at"
  end

  create_table "measurements", force: :cascade do |t|
    t.integer  "fashion_model_id", limit: 4
    t.decimal  "feet",                         precision: 10
    t.decimal  "inches",                       precision: 10
    t.decimal  "bust",                         precision: 10, default: 36
    t.decimal  "waist",                        precision: 10, default: 28
    t.decimal  "hips",                         precision: 10, default: 36
    t.decimal  "shoes",                        precision: 10
    t.integer  "dress",            limit: 4
    t.string   "eyes",             limit: 255
    t.string   "hair",             limit: 255
    t.datetime "created_at",                                               null: false
    t.datetime "updated_at",                                               null: false
  end

  create_table "model_profiles", force: :cascade do |t|
    t.integer  "fashion_model_id", limit: 4
    t.string   "phone_number",     limit: 255
    t.date     "birthdate"
    t.text     "bio",              limit: 65535
    t.string   "location",         limit: 255,                  default: "Venice"
    t.string   "gender",           limit: 255
    t.decimal  "rate",                           precision: 10, default: 100
    t.string   "profile_picture",  limit: 255
    t.datetime "created_at",                                                       null: false
    t.datetime "updated_at",                                                       null: false
  end

  add_index "model_profiles", ["fashion_model_id"], name: "index_model_profiles_on_fashion_model_id", using: :btree

  add_foreign_key "bookings", "fashion_models"
  add_foreign_key "fashion_model_photos", "fashion_models"
end

I am trying to filter out data based on the input. For example someone searches for a model with height 5'8", with black eyes, and brown hair, I should display only those models by querying the database.

Therefore, I am trying to use named scopes in the model. I am not sure how do I scope the attributes of the measurement table by writing a scope in the FashionModel model.

I read a few resources online and from what I understood, I wrote something like

scope :eye_color, includes(:measurement).where(measurement: { eyes: "Amber" })

Though I don't want to hardcode Amber into the eyes field, I get an error in my console when trying to access this scope. I do something like

a = FashionModel.all
a.eye_color

This gives me an and ArgumentError: wrong number of arguments (given 0, expected 1) .

I also tried doing this

scope :eye_color, -> (eye_color) { where eyes: eye_color }

and then calling it by a.eye_color("Amber") , which in turn gave me a NoMethodError: undefined method 'measurement' for Class .

So basically I want to scope into the child models from the parent model. Any help is much appreciated! Thanks

Answer 1

Define your scope as:

scope :eye_color, ->(eye_color) {
  includes(:measurements).where(measurements: {eyes: eye_color}) 
}

And then query with a param like:

FashionModel.eye_color("Amber")