Collection_select

I have threes models: countries, states and cities. Countries has_many states and states has_many cities. When I create a new city I want to have a drop-down menu to pick the Country and State. I am not sure how to get the Country model linked with cities.

So I have something like this on the form for creating a new city:

<%= f.collection_select(:country_id, Country.all, :id, :country_name)%>

In the city model I hav开发者_如何学Pythone:

 def country_id  
 end

That allows me to get the page. But I cannot submit the form. If I submit the form I get

unknown attribute: country_id

---

in your form

<%= f.collection_select :country_id, Country.all, :id, :country_name %>

In your model make sure u have

attr_accessible :country_id

hope this works. but again post the relationships