如何在Rails中调试NoMethodError

Question

I'm following the jumpstartlabs blogger tutorial and I'm down to section i5 and struggling with getting a NoMethodError in Authors#new

Here is the stack trace:

NoMethodError in Authors#new
Showing /home/.../blogger/app/views/authors/_form.html.erb where line #16 raised:

undefined method `username' for #<Author:0xb6379068>
Extracted source (around line #16):

  <div class="field">
      <%= f.label :username %><br>
      <%= f.text_field :username %>
  </div>
  <div class="field">
    <%= f.label :email %><br>

Trace of template inclusion: app/views/authors/new.html.erb

The new.html.erb is really simple

<h1>New Author</h1>

<%= render 'form' %>

<%= link_to 'Back', authors_path %>

And here is my _form.html.erb

<%= form_for(@author) do |f| %>
  <% if @author.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@author.errors.count, "error") %> prohibited this author from being saved:</h2>

      <ul>
      <% @author.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
      <%= f.label :username %><br>
      <%= f.text_field :username %>
  </div>
  <div class="field">
    <%= f.label :email %><br>
    <%= f.text_field :email %>
  </div>
<div class="field">
  <%= f.label :password %><br />
  <%= f.password_field :password %>
</div>
<div class="field">
  <%= f.label :password_confirmation %><br />
  <%= f.password_field :password_confirmation %>
</div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

I really want to know what I can do in the rails console to debug this. Or how to read the trace to figure out why this is occuring. I can attach more of the full trace if needed but it's pretty long.

Answer 1

The rails error message is clear enough. It says that the instance of Author class doesn't respond to username . Ensure you have defined your data model correctly and upplied all database migrations (you must have a username field in authors table). Run rails console ( rails c ) and try Author.new.username to check, or Author.new.attributes to list defined attributes.