undefined method for nil:NilClass when render new post form and @posts together

Question

It's a very strange bug bugged me for couple of hours already.

There are 3 models: user, school, post. Basically on the school page(school#show), there are a list of posts, and user can make new post.

The school controller:

def show
  @school = School.find(params[:id])
  $current_school = @school
  @post = @school.posts.build if logged_in?
  @posts = @school.posts

The school/show.html.erb:

<div>
  <aside>
      <%= render 'shared/post_form' %>
  </aside>
</div>


<div>
  <% if @school.posts.any? %>
      <%= render @posts %>
  <% end %>
</div>

_post_form.html.erb:

<%= form_for(@post) do |f| %>
  <%= render 'shared/error_messages', object: f.object %>
  <div class="field">
    <%= f.text_area :content, placeholder: "Compose new post..." %>
  </div>
  <%= f.submit "Post", class: "btn btn-primary" %>
<% end %>

posts/_post.html.erb:

<li>
  <%= image_tag post.user.avatar.url(:thumb) %>
  <span class="user"><%= link_to post.user.name, post.user %></span>
  <span class="content"><%= post.content %></span>
</li>

Post controller:

def create
  @post = $current_school.posts.create(content:params[:post[:content],user_id:current_user.id)
  if @post.save
    flash[:success] = "Post created!"
    redirect_to $current_school
  else
    render 'static_pages/home'
  end
end

The problem is, when navigate to school#show, it says

undefined method `avatar' for nil:NilClass

If I delete the

      @post = @school.posts.build if logged_in?

line, and the _post_form.html.erb fragment, the list of posts shows fine. If I delete the _post.html.erb fragment, the new post function works fine as well.

But when they exist together, error comes up.

I guess the problem is at this line:

@post = @school.posts.build if logged_in?

because when I comment it out, the list of post shows fine. When I add it back, @posts can return a list of valid post, but post is nil.

Couldn't figure out what's wrong, please help.

Thanks

Edit: when visit url/schools/1, it crashes with NilClass error, post command returns

#<Post id: nil, content: nil, user_id: nil, school_id: 1, created_at: nil, updated_at: nil>

However, it should return the first post from @posts

Is it possible that

    @post = @school.posts.build if logged_in?

assign @post a nil post, and when it renders @posts, it is looking for @post which become nil instead of first post in @posts? If so, how can I correct this?

Edit2: I tried to change @post to @test:

@test = @school.posts.build if logged_in?

and the same nilClass error persists. So my previous guess is not valid. There should be something wrong with using build here. But what's wrong?

Your view doesn't check logged in like the action does, are you 'logged in' according to your code? — Maya Webster, Jun 10 '15 at 20:55
In your post controller's `create` action, `@post = $current_school.posts.create(...` is saving the record (or attempting to). I believe you want that to be `@post = $current_school.posts.new(...` so that the next lines can evaluate whether the save was successful. Just something I noticed, not sure if it's a cause of your issue. Also, `<% if @school.posts.any? %>` can be shortened to `<% if @posts %>`, since `@posts` will be `nil` if none are returned from your school controller's `@posts = @school.posts` line. — digijim, Jun 10 '15 at 22:07

score 1 · Accepted Answer · answered Jun 10 '15 at 21:37

1

Your Post does not have a User associated with it on the new/show action, unless you're somehow plugging a user in on the model. Try:

@post = @school.posts.build(user: current_user) if logged_in?

answered Jun 10 '15 at 21:37

jmdeldin

5,354
1
28
21

You are right! It works following your suggestion! Thank you so much – alexZ Jun 10 '15 at 21:48
Glad it worked for you! Echoing the advice in http://stackoverflow.com/a/30767639/73492 -- pry is really handy for debugging these issues. Just throw a `require 'pry'; binding.pry` line in your controller before the problematic line, and then you can debug `@post`, etc. – jmdeldin Jun 11 '15 at 02:29

score 0 · Answer 2 · answered Jun 10 '15 at 21:18

0

This line: @post = @school.posts.build if logged_in?, should be without build method. Like this: @post = @school.posts if logged_in?

answered Jun 10 '15 at 21:18

caspg

399
1
6

I've tried it. it then reports error undefined method `to_key' , because <%= form_for(@post) do |f| %> needs a new or build method. If I add build here: <%= form_for(@post.build) do |f| %>, it reports the same nilClass error – alexZ Jun 10 '15 at 21:19
But still I think you don't want to use this method, `build` is an alias for `new` [source](https://github.com/rails/rails/blob/master/activerecord/lib/active_record/relation.rb#L124) – caspg Jun 10 '15 at 21:23
If not using it, how can I create a new post? – alexZ Jun 10 '15 at 21:25
First of all, here is an answer why global variables [are bad](http://stackoverflow.com/questions/484635/are-global-variables-bad/485020#485020). – caspg Jun 10 '15 at 21:34
Thanks, I'll try to eliminate the global variable – alexZ Jun 10 '15 at 21:48

score 0 · Answer 3 · answered Jun 10 '15 at 21:30

Please try @post=@school.posts if logged_in? and see if it works. Also another important debugging thing that I can tell you is the gem 'pry'.Install it and you can check the value of variables anywhere in your views/models/controllers.

Hope it helps.

undefined method for nil:NilClass when render new post form and @posts together

3 Answers3