admin_page_controller.rb

class AdminPageController < ApplicationController
	def index
		@gardener = Gardener.all
	end
	def show
		@gardener = Gardener.all
	end
end

error_message.txt

undefined method `group_name' for nil:NilClass

gardener.rb

class Gardener < ActiveRecord::Base
  belongs_to :group
  has_one :user, through: :group
end

schema.rb

# encoding: UTF-8
# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# Note that this schema.rb definition is the authoritative source for your
# database schema. If you need to create the application database on another
# system, you should be using db:schema:load, not running all the migrations
# from scratch. The latter is a flawed and unsustainable approach (the more migrations
# you'll amass, the slower it'll run and the greater likelihood for issues).
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 20150304235455) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"

  create_table "gardeners", force: true do |t|
    t.string   "first_name"
    t.string   "last_name"
    t.integer  "contact_number",      limit: 8
    t.string   "address"
    t.integer  "group_id"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.integer  "id_number",           limit: 8
    t.string   "avatar_file_name"
    t.string   "avatar_content_type"
    t.integer  "avatar_file_size"
    t.datetime "avatar_updated_at"
    t.string   "resume_file_name"
    t.string   "resume_content_type"
    t.integer  "resume_file_size"
    t.datetime "resume_updated_at"
    t.string   "race"
  end

  add_index "gardeners", ["group_id"], name: "index_gardeners_on_group_id", using: :btree

  create_table "groups", force: true do |t|
    t.string   "group_name"
    t.string   "area"
    t.integer  "user_id"
    t.integer  "avatar"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "group_picture_file_name"
    t.string   "group_picture_content_type"
    t.integer  "group_picture_file_size"
    t.datetime "group_picture_updated_at"
  end
  
  create_table "users", force: true do |t|
    t.string   "email",                  default: "", null: false
    t.string   "encrypted_password",     default: "", null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,  null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "name"
    t.integer  "role"
  end

  add_index "users", ["email"], name: "index_users_on_email", unique: true, using: :btree
  add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree

end

show.html.erb

<table class="pretty">
	<tr>
  		<th> <% link_to "name" %> </th>
  		<th> <% link_to "group" %> </th>
  		<th> <% link_to "area" %> </th>
  		<th> <% link_to "trainer" %> </th>
 	</tr>
 <% @gardener.each do |gardener|  %>
 	<tr>
 		<td> <%= gardener.first_name %> </td>
 		<td> <%= gardener.group %> </td>
 		<td> <%= gardener.user %> </td>
 	</tr>
 	<% end %>
 	</table>
 	<%#<%= will_paginate @gardener %>