Julia Evans

Day 1: a confusing Rails error message

Today I started an Recurse Center batch! I got to meet a few people, and started on a tiny fun Rails project. I think I won’t talk too much about what the project actually is today, but here are some quick notes on a day with Rails:

some notes on getting started

The main thing I learned about setting up a Rails project is that

  1. it uses sqlite by default, you have to tell it to use Postgres
  2. there are a ton of things that Rails includes by default that you can disable.

I installed and rm -rf’d Rails maybe 7 times before I was satisfied with it and ended up with this incantation:

rails new . -d postgresql --skip-sprockets --skip-javascript`

Basically because I definitely wanted to use Postgres and not sqlite, and skipping sprockets and javascript seemed to make installing Rails faster, and I figured I could install them later if I decided I wanted them.

the official Rails guide is really good

I used 2 main resources for creating my starter Rails app:

a mysterious error message: undefined method 'user'

I love bugs, so here’s a weird Rails error I ran into today! I had some code that looked like this:

@user = User.new(user_params)

Pretty simple, right? But when that code ran, I got this baffling error message:

undefined method `user' for #<User:0x00007fb6f4012ab8> Did you mean? super 

I was EXTREMELY confused about what was going on here because I hadn’t called a method called user. I’d called .save. What???? I stayed confused and frustrated about this for maybe 20 minutes, and then finally I looked at my User model and found this code:

class User < ApplicationRecord

  validates :user, presence: true, uniqueness: true

validates :user... was supposed to be some Rails magic validating that every User had a username, and that usernames had to be unique. But I’d made a typo, and I’d written user and not username. I fixed this and then everything worked! hooray!

I still don’t understand how I was supposed to debug this though: the stack trace told me the problem was with the @user.save line, and never mentioned that validates :user thing at all. I feel like there must be a way to debug this but I don’t know what it is.

The whole point of me playing with Rails is to see how the Rails magic plays out in practice so this was a fun bug to hit early on.

a simple user management system

I decided I wanted users in my toy app. Some Googling showed me that there’s an extremely popular gem called devise that handles users. I found the README a little overwhelming and I knew that I wanted a very minimal user management system in my toy app, so instead I followed this guide called Authentication from Scratch with Rails 5.2 which seems to be working out so far. Rails seems to already have a bunch of built in stuff for managing users – I was really surprised by how short that guide was and how little code I needed to write.

I learned while implementing users that Rails has a built in magical session management system (see How Rails Sessions Work. By default all the session data seems to be stored in a cookie on the user’s computer, though I guess you can also store the session data in a database if it gets too big for a cookie.

It’s definitely kind of strange to already have a session management system and cookies and users without quite knowing what’s going on exactly, but it’s also kind of fun! We’ll see how it goes.

tomorrow: more rails!

Maybe tomorrow I can actually make some progress on implementing my fun rails app idea!

A new way I'm getting feedback on my zines: beta readers! Day 2: Rails associations & dragging divs around