Scaffold Rails Model

user-invocable: true allowed-tools: Read, Write, Edit, Bash, Glob, Grep argument-hint: <name> <field:type ...>

Description

Generates a Rails model with migration, fixtures, and tests. The first argument is the model name, followed by field definitions (e.g., widget name:string weight:integer).

Steps

1. •

   Generate the model by running:

   code

   bin/rails generate model <name> <fields...>
   

2. •

   Run the migration:

   code

   bin/rails db:migrate
   

3. •

   Add fixture entries in test/fixtures/<plural_name>.yml

4. •

   Update the model test at test/models/<name>_test.rb

Templates

Fixtures

Follow the existing pattern from test/fixtures/users.yml. Create 2-3 meaningful fixture entries:

# test/fixtures/<plural_name>.yml
one:
  <field>: <sensible default value>
  <field>: <sensible default value>

two:
  <field>: <sensible default value>
  <field>: <sensible default value>

• •Use descriptive fixture names when possible (not just one/two)
• •Use ERB for dynamic values: <%= Time.current %>, <%= BCrypt::Password.create("pass") %>
• •For references/belongs_to, use fixture names: user: admin
• •Ensure fixture values are valid and internally consistent

Model Test

Follow this exact pattern from test/models/user_test.rb:

# frozen_string_literal: true

require "test_helper"

class <ModelName>Test < ActiveSupport::TestCase
  test "fixture is valid" do
    <model> = <plural>(:one)
    assert <model>.valid?
  end

  # Add tests for:
  # - Validations (presence, uniqueness, format, etc.)
  # - Associations (has_many, belongs_to, etc.)
  # - Custom methods
  # - Scopes
end

Key Patterns

• •frozen_string_literal: true on all Ruby files
• •require "test_helper" at top of test files
• •Access fixtures by name: widgets(:one), users(:admin)
• •fixtures :all is loaded globally — no need to declare fixtures in tests
• •Test class inherits ActiveSupport::TestCase
• •Use assert, assert_equal, assert_not, assert_respond_to, assert_includes, assert_difference

Notes

• •The model name should be singular (e.g., widget, not widgets)
• •Field types: string, text, integer, float, decimal, boolean, date, datetime, references
• •For references fields, the generator creates belongs_to automatically
• •After generation, review the model file to add any additional validations or associations as appropriate
• •The generator creates the migration, model file, test file, and fixture file — update the latter two with proper content