Question

In my Ruby on Rails application, each group has_many :expenses. I have nested my routes, so expenses are entered only as child entities of their parent groups. Here’s an excerpt from routes.rb.

resources :groups do
    resources :expenses
end

I cannot figure out how to render the ‘new’ action in the case of an expense not saving when it is submitted through /groups/:group_id/expenses/new. In my expenses_controller.rb, here is how the create action is defined:

def create
    @expense = Expense.new(params[:expense])
    @expense.group_id = params[:group_id]
    if @expense.save
      redirect_to group_expense_path(@expense.group.id, @expense.id)
    else
      render 'new'
    end
end

Everything works fine if I satisty expense validation and @expense.save winds up working. However, when it fails and the code tries to render ‘new’ I get:

undefined method `expenses_path' for #<#<Class:0x007fd408b1fd58>:0x007fd408f21ca8>

So, I am assuming I have something about my nested routing wrong. How do I return the user to the new form but still display to him/her through the flash[] params the errors with the data they originally attempted to submit?

Answer 1

The problem is that @group is not initialized

So in your controller just do

@expense = Expense.new(params[:expense])
@group = Group.find(params[:group_id])
@expense.group_id = @group.id