Rails select_tag and data validation

edit.html.erb

<%= form_for @my_model, html: { class: 'form-horizontal' } do |f| %>
  <%= f.label :id, class: 'control-label %>
  <div class="controls">
    <%= f.select(:id, MyModel.all.pluck(:name, :id), include_blank: 'Select') %>
  </div>
<% end %>

my_model.rb

class MyModel < ActiveRecord::Base
  # ID can't be null or blank.
  validates :id, presence: true, allow_blank: false
end

my_models_controller.rb

class MyModelontroller < ApplicationController
  def edit
  end
  
  def update
    if @my_model.update(my_model_params)
      # Updated successfully.
      redirect_to my_model_path(@my_model), notice: 'Model was successfully updated.' }
    else
      # Fail to update, eg. id is blank.
      if @my_model.errors.any?
        flash[:error] = @my_model.errors.full_messages.first
      end
      
      render action: 'edit'
    end
  end
  
  private
  def my_model_params
    params[:my_model].permit! # Permit all fields.
  end
end