ruby 22 lines · 7 steps

Enforcing order-item integrity in Rails

A migration and model that guard order-item data at both the database and application layers.

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Rails Intermediate migrations foreign-keys validations check-constraints data-integrity
1class CreateOrderItems < ActiveRecord::Migration[7.1]
2 def change
3 create_table :order_items do |t|
4 t.references :order, null: false, foreign_key: { on_delete: :cascade }
5 t.references :product, null: false, foreign_key: true
6 t.integer :quantity, null: false, default: 1
7 t.decimal :unit_price, precision: 10, scale: 2, null: false
8 
9 t.timestamps
10 end
11 
12 add_check_constraint :order_items, "quantity > 0", name: "quantity_positive"
13 end
14end
15 
16class OrderItem < ApplicationRecord
17 belongs_to :order
18 belongs_to :product
19 
20 validates :quantity, numericality: { greater_than: 0 }
21 validates :unit_price, numericality: { greater_than_or_equal_to: 0 }
22end
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Database constraints and model validations are complementary defenses, not redundant ones.
  2. 2Cascading foreign keys let the database clean up dependent rows automatically when a parent is deleted.
  3. 3Check constraints enforce business rules like positivity even against writes that bypass the model.

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