Rails task printing tables sorted by foreign key dependencies

db.rake

namespace :db do
  desc "Prints tables sorted by foreign key dependencies"
  task fk: :environment do
    connection = ActiveRecord::Base.connection
    ignored_tables = [ActiveRecord::Base.schema_migrations_table_name, ActiveRecord::Base.internal_metadata_table_name]
    fs_names = connection.tables.sort - ignored_tables
    foreign_keys = fs_names
      .map { |table_name| connection.foreign_keys(table_name) }.flatten
      .map { |foreign_key| { 'from': foreign_key.from_table, 'to': foreign_key.to_table } }.uniq

    print "       tables: "; p fs_names
    print " foreign keys: "; p foreign_keys

    def sort_by_dependencies(unsorted, dependencies)
      left = unsorted
      sorted = []
      dependencies = dependencies.select{ |d| left.include?(d[:from]) && left.include?(d[:to]) }
      while !left.empty?
        exclude = dependencies.map{ |d| d[:from] }.uniq
        add = left - exclude
        sorted = sorted + add
        if add.empty?
          warn "Circular dependencies"
          return unsorted
        end
        left = left - add
        dependencies = dependencies.select{ |d| !add.include?(d[:to]) }
      end
      sorted
    end

    print "sorted tables: "; p sort_by_dependencies(fs_names, foreign_keys)
  end
end