[#]: collector: (lujun9972) [#]: translator: ( ) [#]: reviewer: ( ) [#]: publisher: ( ) [#]: url: ( ) [#]: subject: (Day 1: a confusing Rails error message) [#]: via: (https://jvns.ca/blog/2020/11/09/day-1--a-little-rails-/) [#]: author: (Julia Evans https://jvns.ca/) 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: * DHH’s original Rails talk from 2005 (which I didn’t watch this time, but I watched the last time I spent a day with Rails, and I found it pretty inspiring and helpful) * The official Rails “getting started” guide, which seems pretty short and clear ### 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) @user.save ``` Pretty simple, right? But when that code ran, I got this baffling error message: ``` undefined method `user' for # 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 has_secure_password validates :user, presence: true, uniqueness: true end ``` `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][1] 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][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][3]. 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! -------------------------------------------------------------------------------- via: https://jvns.ca/blog/2020/11/09/day-1--a-little-rails-/ 作者：[Julia Evans][a] 选题：[lujun9972][b] 译者：[译者ID](https://github.com/译者ID) 校对：[校对者ID](https://github.com/校对者ID) 本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 [a]: https://jvns.ca/ [b]: https://github.com/lujun9972 [1]: https://github.com/heartcombo/devise [2]: https://medium.com/@wintermeyer/authentication-from-scratch-with-rails-5-2-92d8676f6836 [3]: https://www.justinweiss.com/articles/how-rails-sessions-work/