rails - collection_select selected value if defined?

I have the following:

<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, :selected => 2 %>

Problem is I only want the selected value of 2 if the value @permission.role_id is nil.

so I tried:

<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, {:selected => 2 if @permission.role_id.nil?} %> 

but that made Rails angry. How can I make a condition selected value based on if a separate variable is nil or not?

Thanks

ok I guess I'll feel stupid in 2 mins, but what about

<%= f.collection_select :role_id, roles, :id, :name, prompt: true, @permission.role_id ? {} : {selected: 2 } %>

The reason why your solution is not working is that your if can return nil, therefor looking something like that:

<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, {nil} %>

Where {nil} is syntax error

While the accepted solution with the ternary operator works, I don't think it is quite as readable as the following solution:

<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, :selected => @permission.role_id || 2 %>

put this in your helper

def selected(permission)
  if permission.role_id.nil?
    return 2
  else
    .....
  end
end

and this in your view

<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, :selected => selected(@permission) %>

The problem is that you can't have an if in that position. So a first solution, though a bit ugly, is something like the following:

<% if @permission.role_id.nil? %>
  <%= f.collection_select :role_id, roles, :id, :name, :prompt => true, {:selected => 2} %>
<% else %>
  <%= f.collection_select :role_id, roles, :id, :name, :prompt => true %>
<% end %>

I found @ecoologic's answer didn't work for me as ruby attempted to interpret the hash as a key for a last argument instead of looking inside the hash for values.

The solution was to use a 'splat'. However splats don't seem to work in that inline format, so I used the following:

<% selected = @permission.role_id ? {} : {selected: 2 } %>
<%= f.collection_select :role_id, roles, :id, :name, prompt: true, **selected %>