---
title: Install Factory Bot with Ruby on Rails
slug: install-factory-bot-with-ruby-on-rails
published_at: 2021-07-09 15:00:24 +0000
updated_at: 2026-03-04 20:14:05 +0000
summary: 
description: In this episode, you&#39;ll learn how to setup the factory_bot_rails gem and some basics about using factories with RSpec tests in a Ruby on Rails application. #rails #rubyonrails
tags: [Install Factory Bot with Ruby on Rails, Add FactoryBot to Rails, Add Factory Bot to Rails, Install FactoryBot to Rails, factory_bot_rails, Configure factory bot with ruby on rails, ruby on rails tutorial, rspec factory bot, factory_bot_rails rspec, factorybot rspec, factorybot rails, ruby on rails rspec]
views: 12301
author: CJ Avilla
url: https://www.cjav.dev/videos/install-factory-bot-with-ruby-on-rails
youtube_url: https://www.youtube.com/watch?v=vQQKIyAHPI4
youtube_id: vQQKIyAHPI4
embed_url: https://www.youtube.com/embed/vQQKIyAHPI4
thumbnail_url: https://i.ytimg.com/vi/vQQKIyAHPI4/hqdefault.jpg
type: video
---

# Install Factory Bot with Ruby on Rails

*Published: July 09, 2021*
*Views: 12301*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=vQQKIyAHPI4)

[![Install Factory Bot with Ruby on Rails](https://i.ytimg.com/vi/vQQKIyAHPI4/hqdefault.jpg)](https://www.youtube.com/watch?v=vQQKIyAHPI4)

## Description

In this episode, you&#39;ll learn how to setup the factory_bot_rails gem and some basics about using factories with RSpec tests in a Ruby on Rails application.
#rails #rubyonrails

## Transcript

what&#39;s up in the last episode you learned about setting up r-spec rails the test framework for running r-spec tests in a rails application this is the the main and primary fundamental tool that i use for running r-spec tests for production applications the other main tool that i use is factory bots we&#39;re going to set that up today so i&#39;m going to jump into the gem file and in the last episode we added the r-spec rails gem directly to a test group now i&#39;m going to use factory bot rails as part of both development and test because it can be kind of handy when you&#39;re in irb or in rails console or pry rails or whatever to just rely on factories that you&#39;ve already created for test mode to sort of configure a user or configure sort of pieces of data with with predefined things that you might want already so if we say gem factory bot rails and then bundle install this will add the factory bot gem to our rails application similar to our spec rails factory bot rails comes with some generators so if we again run rails g model dummy and just see what generators are going to be run we&#39;ll be able to take a look and you&#39;ll notice that as part of the r-spec generators that are executing we also see a factory bot execute a generator execute and it&#39;s creating this new dummies file dummies.rb factory inside of spec factory so let&#39;s go take a look at that and so when you first create a model by default if there&#39;s no fields on the model then the factory is going to be empty like this let&#39;s actually go and rails d model dummy we&#39;ll remove this and then regenerate one with a couple fields just to see the the difference there so we&#39;ll say rails g model dummy and we&#39;ll give it like a name and maybe an age that is an integer and perhaps like a birth born at which is a date time and this should give us a little bit more interesting output okay and then if we open up this factory now you&#39;ll see that there&#39;s a couple things that were filled in for us so this is the factory bot syntax for defining a factory so we&#39;re creating a new factory called dummy and inside of that factory it has three properties uh or three fields three columns in the database three whatever and one of them is going to return a string and so that this name property here when we create a new dummy this will execute the block that we&#39;re passing as an argument to the name method and whatever the return value is from the block that&#39;s what it&#39;s going to use as the value on the new dummy object so if we were to say something like dummy is equal to factory bot dot create and pass in dummy then dummy dot name would equal my string something like this okay similarly you can see it happening for the uh the date time for born at and also the ages returning an integer so that&#39;s kind of that stuff is all sort of interesting okay but before we can write any tests or do anything we first need to run our migration so i&#39;m going to say rails g or rails db colon migrate now when you run migrations it&#39;s going to run them in potentially several environments so it&#39;s going to migrate a locally when you run the migrations it&#39;s going to make the database changes to your development database but it will also make those changes to a test database so there&#39;s actually two different databases here so if we actually jump into like database dot yaml you&#39;ll see that we have our default sort of adapter with our setup we have a development database and this is the name of it form for tracker underscore development and then we separately have a test database form for tracker underscore test so they&#39;re two separate databases and then furthermore there&#39;s going to be a production database that&#39;s a third database that&#39;s the one that lives on heroku when we deploy or wherever you are in production and so that is those are like the three different databases when you run the migrations locally it&#39;s running development and test the migrations for those so that when you are interacting with models in test mode they&#39;re not messing with your development data or your production data so there&#39;s a couple of of like uh foot guns or things to watch out for when you&#39;re working with uh testing and test data but in particular and that is to never ever point your test suite at a production or even at a development database always make sure that your test suite is pointing at its own specific database this is a really common um mistake that uh or this is this is a yeah this is not necessarily a super common mistake but this is a mistake that has happened at major companies where databases were deleted or dropped production databases and they had to be restored because a test suite was pointed at a production database so that&#39;s something to keep in mind is like always be really careful about updating those settings so that you don&#39;t actually run test mode data against your production database because one of the tools too that&#39;s common within rails is called database cleaner and this goes through and deletes like all of the data in the database after your whole test suite runs it makes your tests run faster locally but it&#39;s super dangerous to accidentally point that at a production and then just delete all of your data in production so um yeah that was just sort of an aside about don&#39;t accidentally delete your production database all right so now we&#39;ve got our database models uh migrated let&#39;s open up this dummy spec model and just talk about how we might use this factory so we&#39;ll say like it maybe it like must have an age greater than 21 or something and now we can say dummy is equal to factory bot.create dummy we pass in the symbol which is the name of the thing that we want to create and we get back in this case we&#39;re going to get back an actual instance of a dummy object so we&#39;re going to get back a a dummy model instance and because we&#39;re using create that model will be persisted to the database so now we can say something like expect dummy.age.2 i think it&#39;s b and then you put greater than 21 or something like this or maybe greater equal than 21 let&#39;s see if this runs i can&#39;t actually remember the syntax all right so in this case we said we expected it to be greater than or equal to 21 and we got back one and that&#39;s because in our dum or in our factory um so if we go to our factories here into the dummies factory when our dummy is created its age is being returned as one here so what we could do is we could change this to 21 and now our test will pass but that doesn&#39;t actually like we&#39;re not so to be clear too we&#39;re not actually testing anything at this point right so let&#39;s change this to actually just be some random number so if we said like ran from 1 to 100 right and then we ran the tests now our tests are going to be a flaky test where it&#39;s randomly going to be generating data about this user but it&#39;s going to be different every single time so potentially what we what we might want to do is when we&#39;re writing our test that must have an age greater than 21 or something like we would we could potentially pass in that age so we could say age is equal to whatever 21 and now that will pass and it will be specifically 21. so you can have a factory that&#39;s going to create instances and then let&#39;s say like 4y and then we can come down here and then we could also change it so that actually yeah we could also just change this so that it it fails um and we can see the failing test so that we know that like what we&#39;re passing in is what it actually is so it says expected the dummy age to be greater than or equal to 21 we got 11 because that&#39;s what we explicitly passed in so here you can have like a bunch of defaults right that might be set and then you could also pass in specific values here so that can be handy another thing that you might want to do is that if you have some uniqueness constraints so let&#39;s say rails g migration add email to dummy and we&#39;re gonna say email is a string now if we open the migration add email to dummy and we might say something like null false and then we want to add in index to dummies for email unique true rake db migrate so now we&#39;re going to add a uniqueness constraint to our dummy model now we can go back into our um our dummies generator here and now we need to have an email field so if we say email is equal to like i don&#39;t know uh let&#39;s set it to hello at cjav.dev and that&#39;s what will be returned when we create a new instance of a dummy so if we execute this function or execute this test which again is a dummy test we&#39;re not actually testing any of the model&#39;s functionality we&#39;re just kind of exploring what this factory factory box can do for us and let&#39;s say that we&#39;re going to just remove this age situation and we&#39;re going to expect the dummy dot email dot to equal hello at cjav.dev okay so we&#39;re going to run our test everything is fine we get back hello at cjab.dev great now let&#39;s say that we wanted to update our test so that we maybe we needed to create two dummies and they were going to interact with each other so maybe we have dummy one and we have dummy two right and now if we try to run our test you might have some case where like a user is a friend of another user or a user um can like a post of another user and so you need to create two users well in our case the uh the email address field has a uniqueness constraint and so right now when we call when we try to run the migration or when we try to run the test it&#39;s saying this is failing because when it&#39;s creating dummies it both dummies are returning the same email address and so it can&#39;t insert those into the database because they because of this uniqueness constraint and so in this case there&#39;s a couple different options one is that we can use sequence here and this is a common this is a common practice where you pass it a block so sequence is another helper method that comes from factory bot you can pass in the field that you want to sequence that takes a block where there&#39;s a block argument n and we can use that block argument to create like an alias here so then we can we can add in n as an alias as part of our email address and now if we run this test every single time this is executed we&#39;re going to get a new email that has a number in the email address so now we see hello plus one that has like the alias now we get rid of our uniqueness constraint but now our test is failing because we&#39;re no longer matching what this says so if we were to say like okay we want dummy email one to be hello plus one hello plus two whatever this should pass and have two different email addresses okay so now our database constraint is um is met and we&#39;ve kind of got like a factory where we have a unique field and we&#39;re able to just generate new email addresses as we go so that can be handy um and yeah so this is this is how you set up factory bot there&#39;s one other thing i want to show and that is that like inside of your tests for dummy spec here right so everywhere that we&#39;re seeing factory bot dot create this this uh this class name here is only required um or there&#39;s like a shortcut to to calling create and we can actually just remove the entire class factory bot now in order to get access to that create method we need to include um some of the methods that come from factory bot so what we need to do is go tell our spec about how this works and so we can go into i believe we can go into our rails helper here yeah so our spec.configure and we want to tell it about all the methods from factory bots so we need to go into factory bot and in the in the readme for factory bot here there is a guide to configure factory bots you may want to it says you may want to configure your test suite to include factory bot method so we can go to configuration and for rails i yeah so our spec configure factory bot syntax method so i&#39;m going to copy that and then just drop it down here config.include factory bot syntax methods and then we should now be able to just write create instead of writing build um okay and then our test is back to uh back to executing successfully the other thing i wanted to do was run i think yeah okay so we&#39;ve got pry rails so let&#39;s run rails console and open up the rails console and again i want to just show how it&#39;s convenient to operate with these methods directly from um outside of a test it might be handy to say like oh i need a dummy object instead of saying like dummy dot new and passing in like name and age and all the things that you need to pass in instead now we can just say factorybot.com dummy and now we get an actual instance of a dummy back so dummy is a real object and you can tell that we&#39;ve executed this once and so that&#39;s like what&#39;s stored in the database and oops here one thing that you can see is that we&#39;ve actually saved this dummy to the database right so it has an id that id property tells us that it&#39;s in the database so if we say like dummy.all we should get back that one instance of the dummy that we created we could again we could create another dummy here and this is going to now say like dummy dot count now we have two dummies in the database two dummy objects in the database um and so the thing that&#39;s interesting is that we can also say like dummy or like yeah dummy 3 is equal to factory bot dot build dummy and you&#39;ll see now that the id field is nil okay the id field is nil and this is not actually persisted when we say build it&#39;s not going to actually stick this into the database so now if we were to say dummy.count we should still get back too and we do the nice thing about build is that it executes really it makes your tests execute really fast so if you don&#39;t actually need the objects to be persisted into the database you can use dot build and that will speed up your test suite a little bit because you don&#39;t actually have to like write to the database so that&#39;s especially handy if you&#39;re uh writing a humongous test suite that might take hours you might be able to refactor several of the tests to use build instead of create to not actually persist to the database but instead just use the objects in memory um okay so we could even do like dummy three dot age right so if you have simple methods that are on the models that you need to write tests about but you don&#39;t actually need the model to be saved in the database this is a really good handy tool especially i i have found especially in like model specs where you&#39;re just doing kind of unit tests uh you can use build a little bit more frequently then if you&#39;re in like a bigger end to end or system test you will typically want to use create so that when you&#39;re actually going through the entire process of clicking on different elements on your page those are those are really in the database all right so that is how you set up factory bot um it&#39;s worth mentioning that almost every time that i use factory bot i need to go and look up the syntaxes for a lot of these things so i will head in here there&#39;s a lot of ways you can make like nested factories and factories with associations and other things like that so i always head over to the documentation for factory bot and yeah read through this so this is an example where you have a factory that has the name post and then you can just drop in um the the name for another association so like if this post had an associated author you could say just author and that would create the other model using its factory so like this yeah a user this will like create a user object because it knows that an author is an alias for the user class whatever you can this is one of the ways you can create associations you can also anyway like long story short head over to the docs for factory bot to get all the details but in this episode hopefully you were able to take away how to just set up factory bot and get running the final thing i wanted to leave you with was that in application dot rb down here when we set up um when we set up our spec we uh configured some of the generators i believe you can say g dot factory bot um factory bot uh is equal to false or maybe just false and that will disable the the generators for factory bot g dot let&#39;s see go back to the main readme g dot um okay yeah so we can just say g dot factory bought false and that will disable the generators for factory bot but i like to keep them in there so i want to keep those around and yeah i think that&#39;s pretty handy all right so in the next episode we will talk about writing some actual tests for this application we&#39;ll go through the process of um yeah putting a little bit of testing around some of the the methods that we have built into our models and we&#39;ll start with model testing and sort of unit testing first all right thanks so much for watching we&#39;ll see in the next one

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