Ruby on Rails - Database Seeding

Introduction

Database seeding in Rails is the process of populating your database with initial data. This is useful for setting up a development environment with sample data or populating a production database with essential records. This guide will cover how to seed your database in Rails.

Creating Seed Data

Seed data is defined in the db/seeds.rb file. Here is an example of how to create seed data for an Article model:

# db/seeds.rb
Article.create([
  { title: 'First Article', body: 'This is the body of the first article.' },
  { title: 'Second Article', body: 'This is the body of the second article.' },
  { title: 'Third Article', body: 'This is the body of the third article.' }
])
                

Running Seed Files

To run the seed file and populate your database with the seed data, use the following command:

# Run the seed file
rails db:seed
                

This command will execute the code in the db/seeds.rb file and insert the specified records into the database.

Using External Seed Files

You can also organize your seed data into multiple files for better maintainability. Here is an example of how to use external seed files:

# db/seeds/articles.rb
Article.create([
  { title: 'First Article', body: 'This is the body of the first article.' },
  { title: 'Second Article', body: 'This is the body of the second article.' },
  { title: 'Third Article', body: 'This is the body of the third article.' }
])

# db/seeds.rb
load Rails.root.join('db/seeds/articles.rb')
                

In this example, the seed data for articles is placed in a separate file and then loaded from the main seeds.rb file.

Seeding with Environment-Specific Data

You may want to seed your database with different data depending on the environment (development, test, production). Here is an example of how to do this:

# db/seeds.rb
if Rails.env.development?
  Article.create([
    { title: 'Development Article 1', body: 'This is a development article.' },
    { title: 'Development Article 2', body: 'This is another development article.' }
  ])
elsif Rails.env.production?
  Article.create([
    { title: 'Production Article 1', body: 'This is a production article.' },
    { title: 'Production Article 2', body: 'This is another production article.' }
  ])
end
                

Using Factories for Seeding

Factories can be used to generate seed data. This is especially useful for generating large amounts of sample data. Here is an example using the FactoryBot gem:

# db/seeds.rb
10.times do
  FactoryBot.create(:article)
end
                

Rake Tasks for Seeding

Rake tasks can be created for seeding the database with specific data. Here is an example:

# lib/tasks/seed.rake
namespace :db do
  desc "Seed the database with articles"
  task seed_articles: :environment do
    load Rails.root.join('db/seeds/articles.rb')
  end
end

# Run the rake task
rake db:seed_articles
                

Conclusion

Database seeding in Rails is a powerful way to populate your database with initial data. By using the techniques covered in this guide, you can efficiently manage seed data for your development and production environments, ensuring your application starts with the data it needs.