Question

I have a coupon system, and I’m trying to get the coupon object with the method find_by:

Coupon.find_by_coupon(params[:coupon])

I’m getting this error:

ArgumentError Exception: Unknown key: coupon

I’m sure params[:coupon] is right:

(rdb:1) eval params[:coupon]
{"coupon"=>"100"}

I have the following model:

# Table name: coupons
#
#  id              :integer         not null, primary key
#  coupon          :string(255)
#  user_id         :integer

---

UPDATE:

It’s working if I put Coupon.find_by_coupon(params[:coupon][:coupon]) instead of Coupon.find_by_coupon(params[:coupon]).

Here the code with the form in my view:

<%= semantic_form_for Coupon.new, url: payment_summary_table_offers_path(@booking_request) do |f| %>
    <%= f.input :coupon, :as => :string, :label => false, no_wrapper: true %>
    <%= f.action :submit, :as => :button, :label => t(:button_use_coupon), no_wrapper: true,
    button_html: { value: :reply, :disable_with => t(:text_please_wait) } %>
<% end %>

Answer 1

If you are using Rails 3, I advise you to find object using this method:

# equivalent of find_all
Coupon.where(:coupon => params[:coupon]) # => Returns an array of Coupons
# equivalent of find :first
Coupon.where(:coupon => params[:coupon]).first # => Returns a Coupon or nil

Try to do a params.inspect to see exactly how is made your Hash. I think it is built like this:

{ :coupon => { :coupon => '100' } }

If it is, you should use params[:coupon][:coupon] to get the String ‘100’

Following your update:

semantic_form_for is creating the form for you, as you give him a Coupon.new it will build the params this way:

params = {
  :coupon => { :attribute_1 => 'value_1', :attribute_2 => 'value_2' }
}

If you prefer to use the find_by method:

Coupon.find_by_coupon(params[:coupon][:coupon]) # => Returns a Coupon or raise a RecordNotFound error

Or with the where method:

Coupon.where(:coupon => params[:coupon][:coupon]).first # => Returns a Coupon or nil