Rakefile for rails-like functionality with ActiveRecord 6

database.yml

# config/database.yml
host: 'localhost'
adapter: 'postgresql'
encoding: utf-8
database: 'test'

Rakefile

require "active_record"

namespace :db do

  db_config       = YAML::load(File.open('config/database.yml'))
  db_config_admin = db_config.merge({'database' => 'postgres', 'schema_search_path' => 'public'})

  desc "Create the database"
  task :create do
    ActiveRecord::Base.establish_connection(db_config_admin)
    ActiveRecord::Base.connection.create_database(db_config["database"])
    puts "Database created."
  end

  desc "Migrate the database"
  task :migrate do
    ActiveRecord::Base.establish_connection(db_config)
    ActiveRecord::Tasks::DatabaseTasks.migrate
    Rake::Task["db:schema"].invoke
    puts "Database migrated."
  end

  desc "Drop the database"
  task :drop do
    ActiveRecord::Base.establish_connection(db_config_admin)
    ActiveRecord::Base.connection.drop_database(db_config["database"])
    puts "Database deleted."
  end

  desc "Reset the database"
  task :reset => [:drop, :create, :migrate]

  desc 'Create a db/schema.rb file that is portable against any DB supported by AR'
  task :schema do
    ActiveRecord::Base.establish_connection(db_config)
    require 'active_record/schema_dumper'
    filename = "db/schema.rb"
    File.open(filename, "w:utf-8") do |file|
      ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
    end
  end

end

namespace :g do
  desc "Generate migration"
  task :migration do
    name = ARGV[1] || raise("Specify name: rake g:migration your_migration")
    timestamp = Time.now.strftime("%Y%m%d%H%M%S")
    path = File.expand_path("../db/migrate/#{timestamp}_#{name}.rb", __FILE__)
    migration_class = name.split("_").map(&:capitalize).join

    File.open(path, 'w') do |file|
      file.write <<-EOF
class #{migration_class} < ActiveRecord::Migration[6.0]
  def self.up
  end
  def self.down
  end
end
      EOF
    end

    puts "Migration #{path} created"
    abort # needed stop other tasks
  end
end

Note that you can use <<~ in your heredoc to avoid needing to make your indentation harder to read.

i.e.

namespace :g do
  desc "Generate migration"
  task :migration do

    ....

    File.open(path, 'w') do |file|
      file.write <<~EOF
        class #{migration_class} < ActiveRecord::Migration[6.0]
          def self.up
          end
          def self.down
          end
        end
      EOF
    end