---
title: Factory Bot 2.4 Goes Meta
teaser:
tags: news,web,rails,performance,open source,factory_girl,factory_bot
author: Josh Clayton
published_on: 2012-01-13
---

[Factory Bot](https://github.com/thoughtbot/factory_bot)[^1] has been getting some
hardcore internal refactorings over the past few months.
[Traits](https://thoughtbot.com/blog/post/8835133151/never-fear-traits-are-here)
are a great example of something that's started very bare-bones with a few
caveats and been transformed to one of my favorite features of the Factory Bot
syntax. It required a pretty decent chunk of refactoring and there were bugs for
quite a while due to the way attributes in general were handled.

## The Old Way

Internally, Factory Bot has four different types of attributes (Dynamic,
Static, Association, and Sequence); when compiling attributes, we were sorting
attributes by the order attributes were added, moving all static attributes to
the beginning of the list (with a `priority` attribute). This worked for 99% of
all cases but did have bugs ([the most recent involved traits and dynamic
attributes](https://github.com/thoughtbot/factory_bot/issues/247)). I wanted to
resolve this once and for all.

## The New Way

Factory Bot now creates a new class per factory ([with some awesome usage of
`Class.new`](https://github.com/thoughtbot/factory_bot/commit/f2e41389)) and
defines methods on that class for each attribute declared in the factory files.
This means Factory Bot doesn't have to worry about sorting attributes anymore;
every attribute is effectively lazily-evaluated so it'll return the correct
value every time. Factory Bot also uses inheritance for these anonymous
classes, resulting in a pretty significant speedup of factory interaction
(namely because we were copying all parent attributes and callbacks to each
child to mimic inheritance before).

## What Does It Mean

Factory Bot is now faster!

Here's some benchmarks from Factory Bot 2.3.0:

                                    user     system      total        real
    build x10000                4.920000   0.010000   4.930000 (  5.028088)
    trait build x10000          6.180000   0.010000   6.190000 (  6.296030)
    inline trait build x10000   5.870000   0.010000   5.880000 (  5.989512)
    deep build x10000           8.100000   0.020000   8.120000 (  8.285039)
    attributes_for x10000       3.200000   0.010000   3.210000 (  3.289043)
    create x500                 1.010000   0.320000   1.330000 (  4.186271)

And from Factory Bot 2.4.0:

                                    user     system      total        real
    build x10000                3.050000   0.000000   3.050000 (  3.121359)
    trait build x10000          3.260000   0.010000   3.270000 (  3.353590)
    inline trait build x10000   6.700000   0.040000   6.740000 (  7.037460)
    deep build x10000           3.400000   0.010000   3.410000 (  3.503984)
    attributes_for x10000       0.820000   0.010000   0.830000 (  0.886641)
    create x500                 0.710000   0.310000   1.020000 (  3.980102)

Grab a copy of [Factory Bot
2.4.0](http://rubygems.org/gems/factory_girl/versions/2.4.0) and speed up your
suite!

[^1]: Looking for FactoryGirl? The library was renamed in 2017.
[Project name history can be found here.](https://github.com/thoughtbot/factory_bot/blob/master/NAME.md)