db_clean.rake

# lib/tasks/db_clean.rake
# Homemade rake task to clean DB for Rails 5

namespace :db do
  desc "Reset and seed DB"
  task :clean => :environment do
    # Empty tables and reset primary id autoincrement
    ApplicationRecord.connection.tables.each do |table|
      next if table.match(/\Aschema_migrations\Z/) || table.match(/\Aar_internal_metadata\Z/)
      ApplicationRecord.connection.execute("TRUNCATE TABLE #{table} RESTART IDENTITY CASCADE")
    end

    # Seed
    sh "rails db:seed"
  end
end

You can just do rails db:clean to run it.