Question

I am a rails newbie, have a simple question:
I have two tables, valor, belongs to an object at the variables table

On the page of a single variable, I put the following link:

<%= link_to 'Novo Valor', :controller => "valors", :action=> 'new', :id=>@variable%>

So the URL appears as: http://localhost:3000/valors/new?id=1

But how do I use the id value represented at the URL in order to create a new valor object with the foreign key variable_id=1?

Answer 1

Something like:

# Your action
def new
  @valor = Valor.new(:variable_id => params[:id])
end

# Then in the view:
<%= form_for(@valor) do |f| %>
  ...
<% end %>

You could also simplify the action and make it more flexible by passing the full object parameters in the same way create and update works, like:

def new
  @valor = Valor.new(params[:valor] || {})
end

# making your link:
<%= link_to 'Novo Valor', :controller => "valors", :action=> 'new', :valor => { :variable_id => @variable } %>

This makes the generated URL a bit uglier, but would allow you to pass arbitrary creation parameters to the new record, rather than manually building them in the controller.

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Side note, given that you’re using standard resourceful routes, you could simplify the link generation by using the named route for a new Valor:

<%= link_to 'Novo valor', new_valor_path(:valor => { :variable_id => @variable }) %>