背景：

之前做课设的时候用 ROR Tutorial 学了一段时间的 Rails。现在想自己深入学一下 Rails 这块，就重新捡起来。而且也想试试 Rails 7 与教程中不兼容的地方，并且解决这些问题来提升自己。 （不过这次我自己搞不定了）

环境：

wsl 1

Gemfile:

# source "https://rubygems.org"
source "https://gems.ruby-china.com"
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby "3.0.2"

# Bundle edge Rails instead: gem "rails", github: "rails/rails", branch: "main"
gem "rails", "~> 7.0.2", ">= 7.0.2.2"

# The original asset pipeline for Rails [https://github.com/rails/sprockets-rails]
gem "sprockets-rails"

# Use sqlite3 as the database for Active Record
gem "sqlite3", "~> 1.4"

# Use the Puma web server [https://github.com/puma/puma]
gem "puma", "~> 5.0"

# Use JavaScript with ESM import maps [https://github.com/rails/importmap-rails]
gem "importmap-rails"

# Hotwire's SPA-like page accelerator [https://turbo.hotwired.dev]
gem "turbo-rails"

# Hotwire's modest JavaScript framework [https://stimulus.hotwired.dev]
gem "stimulus-rails"

# Build JSON APIs with ease [https://github.com/rails/jbuilder]
gem "jbuilder"

# Use Redis adapter to run Action Cable in production
gem "redis", "~> 4.0"

# Use Kredis to get higher-level data types in Redis [https://github.com/rails/kredis]
# gem "kredis"

# Use Active Model has_secure_password [https://guides.rubyonrails.org/active_model_basics.html#securepassword]
gem "bcrypt", "~> 3.1.7"

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem "tzinfo-data", platforms: %i[ mingw mswin x64_mingw jruby ]

# Reduces boot times through caching; required in config/boot.rb
gem "bootsnap", require: false

# Use Sass to process CSS
# gem "sassc-rails"

# Use Active Storage variants [https://guides.rubyonrails.org/active_storage_overview.html#transforming-images]
# gem "image_processing", "~> 1.2"

gem "bootstrap-sass"

group :development, :test do
  # See https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debug-gem
  gem "debug", platforms: %i[ mri mingw x64_mingw ]
  gem "byebug"
end

group :development do
  # Use console on exceptions pages [https://github.com/rails/web-console]
  gem "web-console"

  # Add speed badges [https://github.com/MiniProfiler/rack-mini-profiler]
  # gem "rack-mini-profiler"

  # Speed up commands on slow machines / big apps [https://github.com/rails/spring]
  # gem "spring"

  gem "guard"
  gem "guard-minitest"
end

group :test do
  # Use system testing [https://guides.rubyonrails.org/testing.html#system-testing]
  gem "capybara"
  gem "selenium-webdriver"
  gem "webdrivers"
  gem "minitest-reporters"
  gem "rails-controller-testing"
end

gem "erb-formatter", "~> 0.3.0"

问题：

在ROR Tutorial 7.3 注册失败 - (需要科学上网)，中的 7.3.3 错误消息提示小节。

遇到的困难

错误消息未提示。

尝试解决

经查找，发现是 render 之后的@user为 nil 导致。但是依照代码来说，@user应该留存的是 controller 的值。难道说现在的 Rails 在 render 之后会刷新 erb 中引用 controller 的值吗？

相关代码展示

_errors_messages.html.erb

<% if @user.errors.any? %>
    <div id="error_explanation">
        <div class = "alert alert-danger">
            The form contains <%= pluralize(@user.errors.count, "error") %>
        </div>

        <% @user.errors.full_messages.each do |msg| %>
            <li><%= msg %></li>
        <% end %>
    </div>
<% end %>

users_controller.rb

class UsersController < ApplicationController
  def new
    @user = User.new
  end

  def show
    @user = User.find(params[:id])
  end

  def create
    @user = User.new(user_params)
    if @user.save

    else
      render 'new'
      # debugger
    end

  end

  private 
    def user_params
      params.require(:user).permit(:name, :email, :password, :password_confirmation)
    end
end

new.html.erb

<% provide(:title, 'Sign up') %>
<h1>Sign up</h1>


<div class="row">
    <div class="col-md-6 col-md-offset-3">
        <%= form_for(@user) do |f| %>

        <%= render 'shared/error_messages' %>

        <%= f.label :name %>
        <%= f.text_field :name %>

        <%= f.label :email %>
        <%= f.email_field :email %>

        <%= f.label :password %>
        <%= f.password_field :password %>

        <%= f.label :password_confirmation, "Confirmation" %>
        <%= f.password_field :password_confirmation %>

        <%= f.submit "Create my account", class: "btn btn-primary" %>
        <% end %>
    </div>
</div>

具体代码项目在这 (Github)