Rails 5 error with nested_attributes for a has_one relation

Question

I'm able to get a model Post to be working properly for has_many and accepts_nested_attributes_for model Category. However, I want to limit a post to have only 1 category, which is where I'm failing. Here is the revised code:

# post.rb
has_one :category_tag, :dependent => :delete
has_one :category, through: :category_tag
accepts_nested_attributes_for :category_tag

# posts_controller.rb
def new
  @post = Post.new
  @post.category_tag.build
end

And ^ there is the problem: undefined method 'build' for nil:NilClass
It worked fine when I was using has_many :category_tags in the model and @post.category_tags.build
TIA

SteveTurczyn · Accepted Answer · 2016-11-07 00:54:02Z

2

For has_one relationships the correct format is

@post.build_category_tag

answered Nov 7, 2016 at 0:54

SteveTurczyn

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6 Comments

Akash Agarwal Over a year ago

I'm using rails 5 and the solution sounded weird to me, indeed it isn't working.. undefined method build_category_tag

Akash Agarwal Over a year ago

This is very strange! I switched back to has_many settings to continue working on other aspects of the app. However when you posted the answer(which didn't work), I tried the original line(after switching to has_one settings) @post.category_tag.build again and it worked flawlessly. I remember I did restart the server(which shouldn't be a problem in the first place) when I was trying what I posted.

SteveTurczyn Over a year ago

It should've been created. See guides.rubyonrails.org/…

SteveTurczyn Over a year ago

And the guide specifically says you should not use @post.category_tag.build in has_one because it can lead to orphaned records.

Akash Agarwal Over a year ago

I read everything you pointed out. However I'm unable to debug the cause of problem. Can you guide me somehow?

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