ruby 32 lines · 7 steps

How scopes compose in a Rails model

An Order model layers associations, enums, and reusable scopes that build on each other with subqueries.

Explained by highlit

Rails Intermediate scopes activerecord subqueries query-composition enums

1class Order < ApplicationRecord
belongs_to :customer
has_many :line_items
has_many :products, through: :line_items
5 
enum status: { pending: 0, paid: 1, shipped: 2, cancelled: 3 }
7 
scope :recently_paid, -> {
  where(status: :paid).where(paid_at: 30.days.ago..)
}
11 
scope :for_active_customers, -> {
  where(customer_id: Customer.active.select(:id))
}
15 
scope :containing_discounted_products, -> {
  discounted = Product.where("discount_percentage > 0").select(:id)
  where(id: LineItem.where(product_id: discounted).select(:order_id))
}
20 
scope :high_value_repeat_business, -> {
  repeat_buyers = Order.paid
    .group(:customer_id)
    .having("COUNT(*) >= ?", 3)
    .select(:customer_id)
26 
  for_active_customers
    .where(customer_id: repeat_buyers)
    .where("total_cents >= ?", 25_000)
    .order(total_cents: :desc)
}
32end

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Named scopes return relations, so they chain and nest inside other scopes without triggering queries early.
2Passing a relation to where builds a SQL subquery, keeping filtering in the database instead of loading records into Ruby.
3Small, single-purpose scopes compose into complex business queries that stay readable and reusable.

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