Rails polymorphic has_one build - ruby-on-rails

Question

Given a ContentBlock model:
class ContentBlock < ActiveRecord::Base
has_one :block_association
has_one :image, through: :block_association, source: :content, source_type: "Image"
has_one :snippet, through: :block_association, source: :content, source_type: "Snippet"
accepts_nested_attributes_for :image, allow_destroy: true
accepts_nested_attributes_for :snippet, allow_destroy: true
end
BlockAssociation model:
class BlockAssociation < ActiveRecord::Base
belongs_to :content_block
belongs_to :content, polymorphic: true
end
Snippet model:
class Snippet < ActiveRecord::Base
has_one :block_association, as: :content
has_one :content_block, through: :block_association
validates :body, presence: true
end
I need to do:
#content_block.build_snippet
but this gives:
undefined method 'build_snippet' for #<ContentBlock:0x007ffb7edde330>
How would I achieve the intended result?
The form would be something like this:
<%= simple_form_for #content_block do |f| %>
<%= f.simple_fields_for f.object.snippet || f.object.build_snippet do |sf| %>
<%= sf.input :body %>
<% end %>
<% end %>
(Originally I had assumed that content_block would simply belong_to :content, polymorphic: true but that seemed inadequate due to the multiple content types.)
This is kind of close to what I'm doing, but I just can't quite get my head around it: http://xtargets.com/2012/04/04/solving-polymorphic-hasone-through-building-and-nested-forms/

Answer 1

class ContentBlock < ActiveRecord::Base
has_one :snippet, through: :block_association, source: :content, source_type: "Snippet"
end
This tells rails, you want instances of ContentBlock (lets make content_block this instance) to have one instance of Snippet called "snippet" of the fake-type "content" through BlockAssociation. ContentBlock instances should hence be able to respond to content_block.content which would retourn a collection of a snippet and/or image (I left out the image part in the code-snippets). How content_block can call only snippet content no one knows yet.
What does your BlockAssociation Model know:
class BlockAssociation < ActiveRecord::Base
belongs_to :content_block
belongs_to :content, polymorphic: true
end
It knows it belongs to a content_block and knows (since it will respond to content) one or more contents which have a content_type ('Snippet') and a content_id (1 or whatever snippets id is), the combination of those makes the relation to snippet
Now what you were missing was the Snippet part:
class Snippet < ActiveRecord::Base
has_one :block_association, :as => :snippet_content
has_one :content_block, :through => :content_association # I'm actually not quite sure of this
end
Which tells block_association how to call this type of content, since you want to differ between image-content and snippet-content. Now content_block.snippet_content should return the snippet and snippet.block_content should return block_content.
I hope I didn't mess anything up, these relations allways get my head spinning