Simple_Form display validation error messages next to different input field

Question

I have a form that allows the user to search for existing records to populate an association. Each "Booking" belongs to a "Customer". So the form allows you type the customer's name, it does a search automatically, and you click the customer you want. The input field you're typing into should display the customer's name, but for the form to work, I set the customer_id in a hidden input field.

I'm using the simple_form gem. Does anybody know if I can display the validation errors for the customer_id next to the text input field that displays the customer's name? The customer_id is required in the model, so I need the form to tell the user that if they leave it blank.

View code (simplified -- there's some JavaScript that handles searching when you type into the customer text box, and that sets the value in the hidden field to the customer's id when you make a selection):

<%= simple_form_for @booking do |f| %>
  <%= f.hidden_field :customer_id, id: "customer_id" %>
  <%= f.input :customer, required: true,
      input_html: { value: @booking.customer_name } %>
<% end %>

Answer 1

I eventually found out about the append block in simple_form (buried in a pull request, not documented anywhere else that I could find). Basically, you can use that to append whatever markup you want to your f.input. I did the following, which is pretty hacky, but it does what I need it to do:

<%= f.input :customer, required: true,
    wrapper_html: { class: ("error" if @booking.errors[:customer_id].any?) } do %>
  <%= f.input_field :customer, value: @booking.customer_name %>
  <%= f.error :customer_id %>
<% end %>

First, I had to conditionally add the class "error" to the wrapper if there were any errors on the related field, then I used the append block to render out the input field, followed by the errors for the related field from the model. Hope this helps someone in the future!