Rails: use build to create a model that doesnt exist

Question

Lets say I have a model topic, and it has one moderator. I want to build a new post for a topic.

In my controller:

@topic = Topic.find(:id)
@moderator = @topic.moderator.build # error points to this line

Error:

undefined method `build' for nil:NilClass

score 1 · Accepted Answer · edited May 23 '17 at 11:57

1

If the relation is declared in the model as long as it is a has_many you might have been declared:

has_many :posts

So you need to call:

@post = @topic.posts.build

Suppossing you have a has_one relation:

has_one :moderator

@moderator = @post.build_moderator

Solved here:

edited May 23 '17 at 11:57

Community

answered Jun 11 '14 at 22:10

Thanks for the answer Jorge - do you know what the method if it's a "has_one"? Or where this is documented in Rails? – Don P Jun 11 '14 at 22:12
You've changed the question. I've added the answer to has one. – Jorge de los Santos Jun 11 '14 at 22:14
Thanks! It's strange because when I try your answer for the has_one, I get the `undefined method "build" for nil:NilClass` error. – Don P Jun 11 '14 at 22:16
Edited to fix my mistake. The method changes for has_one – Jorge de los Santos Jun 11 '14 at 22:17
1

See also the Rails guide re: associations. http://guides.rubyonrails.org/association_basics.html – zetetic Jun 12 '14 at 00:13

1 Answers1