Recursively remove data from tables in PGSQL, considering foreign keys

recursive_delete.rb

#!/usr/bin/env ruby

@verbose = true

tables_to_clear = ARGV.dup.freeze

# Alternately, clear out everything but these tables
#UNCLEARED_TABLES=%w{ ar_internal_metadata schema_migrations }
#tables_to_clear = (ActiveRecord::Base.connection.tables.sort - UNCLEARED_TABLES).freeze

# reset a sequence to 0
def reset_sequence(table, id='id', sequence=false)
  sequence="#{table}_#{id}_seq" unless sequence
  ActiveRecord::Base.connection.execute %{select setval('#{sequence}', 1, false)}
end

@dependencies = tables_to_clear.each_with_object({}) do |table_name,o|
  ActiveRecord::Base.connection.foreign_keys(table_name).each do |fk|
    if !UNCLEARED_TABLES.include?(fk.to_table) && !UNCLEARED_TABLES.include?(fk.from_table) && fk.from_table != fk.to_table
      o[fk.to_table] ||= []
      o[fk.to_table].push fk.from_table
    end
  end
end

puts "Clearing old data" if @verbose

# Before I clear "table", I have to clear all tables in dependencies["table"].
# Pray there are no circular dependencies :)
@already_cleared = {}

def recursively_delete_all(table_name)
  if @dependencies[table_name] && @dependencies[table_name].any?
    @dependencies[table_name].each do |dependent_table_name|
      recursively_delete_all(dependent_table_name)
    end
  end
  unless @already_cleared[table_name]
    puts "  " + table_name if @verbose
    ActiveRecord::Base.connection.exec_delete("delete from #{table_name}")
    if ActiveRecord::Base.connection.columns(table_name).any? { |c| c.name == 'id' }
      reset_sequence table_name
    end
    @already_cleared[table_name] = true
  end
end

ActiveRecord::Base.connection.transaction do
  tables_to_clear.each do |table_name|
    recursively_delete_all(table_name)
  end
end