export AR model to sql

sql_dump.rb

# export AR model to sql
# example:
#   SqlDump.new( KeyValue.where(..) ).export{ |sql| puts sql }
#   SqlDump.new( KeyValue.where(..) ).export(file: "key_values_dump.sql")
class SqlDump
  def initialize(scope)
    @scope = scope
    @count = 0
  end

  def export(file: nil) # &block
    if file
      open(file, 'wb') do |f|
        each_block {|sql| f.write(sql); f.write("\n")}
      end
    else
      each_block {|sql| yield sql}
    end
    @count
  end

  def each_block
    @count = 0
    insert_base = nil
    @scope.find_in_batches do |records|
      record = records.first
      insert_base ||= "INSERT INTO #{@scope.quoted_table_name} (#{ record.attributes.keys.map {|n| @scope.connection.quote_column_name(n)}.join(', ') }) VALUES"
      values_sql = records.map do |r|
        "(#{r.attributes.values.map {|v| @scope.connection.quote(v)}.join(',') })"
      end.join(', ')

      yield "#{insert_base} #{values_sql};"
      @count += records.size
      puts @count
    end
  end

end