database design - Rails models has_many -

im starting learn rails today , not quite sure how work:

lets have company, company may have many subsidiaries.

a subsidiary company. company cannot own subsi diary obvious reasons.

a subsidiary cannot have subsidiary subsidiary of company

so subsidiary can have subsidiaries, unlimitedly nested

what im not sure below subsidiary company

class company < activerecord::base     has_many :subsidiaries end class subsidiary < activerecord::base     belongs_to :companies end 

im sure wrong, putting in here

update:

ok, followed instructions below this:

class company < activerecord::base     validates   :name, presence: true     belongs_to :company     has_many :subsidiaries, foreign_key: 'company_id', class_name: 'company' end 

in 1 of templates:

<% @companies.each |company| %>     <li><%= link_to  "#{company.name} #{company.subsidiaries.length > 0 ? "(#{company.subsidiaries.length} subsidiaries)" :"" }", company_path(@company, :id => company.id) %></td> <% end %> 

now show wrong, happens ones subsidiaries shows have no subsidiaries , ones subsidiaries shows have subsidiaries, basicly showing parent's now, "children"

any idea why happens?

what want recursive self relation:

class company < activerecord::base     belongs_to :company     has_many :subsidiaries, foreign_key: 'company_id', class_name: 'company' end 

so, essentially, company belongs company , has many companies. however, have special name it's companies (subsidiaries), give "alias" manually setting relation. might want same "parent" company.

you use validations check conditions.