商品購入ページへ遷移したい

エラー文ではコントローラーのindexアクションの定義がなされていないということで、購入編集ページに遷移できないでいます。使用しているインスタンス変数といたしましては、「formオブジェクトパターン」を利用したものになっています。formオブジェクト使用のモデルの定義も一通りできていると思いますが、うまくできません。どなたかご教授願います。

NoMethodError in PurchaseHistoriesController#index
undefined method `all' for UserItem:Class


app/controllers/purchase_histories_controller.rb

class PurchaseHistoriesController < ApplicationController
  def index
    @user_purchase_histories = UserPurchaseHistory.all
  end

  def new
    @user_purchase_history = UserPurchaseHistory.new
  end

  def create
    @user_purchase_history = UserPurchaseHistory.new(purchase_history_params)
    if @user_purchase_history.valid?
      @user_purchase_history.save
      redirect_to action: :index
    else
      render action: :new
    end
  end

  private

  def purchase_history_params
    params.require(:user_purchase_history).permit(:nickname, :email, :encrypted_password, :first_name, :family_name, :first_name_kana, :family_name_kana)
  end
end

views/parchase_history/index.html.erb

<%= render "shared/second-header"%>

<div class='transaction-contents'>
  <div class='transaction-main'>
    <h1 class='transaction-title-text'>
      購入内容の確認
    </h1>
    <%# 購入内容の表示 %>
    <div class='buy-item-info'>
      <%= image_tag "item-sample.png", class: 'buy-item-img' %>
      <div class='buy-item-right-content'>
        <h2 class='buy-item-text'>
          <%= "商品名" %>
        </h2>
        <div class='buy-item-price'>
          <p class='item-price-text'>¥<%= 999,999,999 %></p>
          <p class='item-price-sub-text'><%= '配送料負担' %></p>
        </div>
      </div>
    </div>
    <%# /購入内容の表示 %>

    <%# 支払額の表示 %>
    <div class='item-payment'>
      <h1 class='item-payment-title'>
        支払金額
      </h1>
      <p class='item-payment-price'>
        ¥<%= "販売価格" %>
      </p>
    </div>
    <%# /支払額の表示 %>

    <%= form_with model: @user_purchase_history, id: 'charge-form', class: 'transaction-form-wrap',local: true do |f| %>
    <%# カード情報の入力 %>
    <div class='credit-card-form'>
      <h1 class='info-input-haedline'>
        クレジットカード情報入力
      </h1>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">カード情報</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.text_field :number, class:"input-default", id:"card-number", placeholder:"カード番号(半角英数字)", maxlength:"16" %>
        <div class='available-card'>
          <%= image_tag 'card-visa.gif', class: 'card-logo'%>
          <%= image_tag 'card-mastercard.gif', class: 'card-logo'%>
          <%= image_tag 'card-jcb.gif', class: 'card-logo'%>
          <%= image_tag 'card-amex.gif', class: 'card-logo'%>
        </div>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">有効期限</label>
          <span class="indispensable">必須</span>
        </div>
        <div class='input-expiration-date-wrap'>
          <%= f.text_area :exp_month, class:"input-expiration-date", id:"card-exp-month", placeholder:"例)3" %>
          <p>月</p>
          <%= f.text_area :exp_year, class:"input-expiration-date", id:"card-exp-year", placeholder:"例)23" %>
          <p>年</p>
        </div>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">セキュリティコード</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.text_field :cvc,class:"input-default", id:"card-cvc", placeholder:"カード背面4桁もしくは3桁の番号", maxlength:"4" %>
      </div>
    </div>
    <%# /カード情報の入力 %>
    
    <%# 配送先の入力 %>
    <div class='shipping-address-form'>
      <h1 class='info-input-haedline'>
        配送先入力
      </h1>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">郵便番号</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.text_field :post_code, class:"input-default", id:"postal-code", placeholder:"例）123-4567", maxlength:"8" %>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">都道府県</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.collection_select(:prefecture_id, Prefecture.all, :id, :name, {}, {class:"select-box", id:"prefecture"}) %>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">市区町村</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.text_field :city, class:"input-default", id:"city", placeholder:"例）横浜市緑区"%>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">番地</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.text_field :house_number, class:"input-default", id:"addresses", placeholder:"例）青山1-1-1"%>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">建物名</label>
          <span class="form-any">任意</span>
        </div>
        <%= f.text_field :building_name, class:"input-default", id:"building", placeholder:"例）柳ビル103"%>
      </div>
      <div class="form-group">
        <div class='form-text-wrap'>
          <label class="form-text">電話番号</label>
          <span class="indispensable">必須</span>
        </div>
        <%= f.text_field :phone_number, class:"input-default", id:"phone-number", placeholder:"例）09012345678",maxlength:"11"%>
      </div>
    </div>
    <%# /配送先の入力 %>
    <div class='buy-btn'>
      <%= f.submit "購入" ,class:"buy-red-btn" %>
    </div>
    <% end %>
  </div>
</div>
<%= render "shared/second-footer"%>

config/routes.rb

Rails.application.routes.draw do
  devise_for :users
  root "items#index"
  resources :items do
    resources :purchase_histories, only: [:index, :new, :create]
  end
end

以下formオブジェクトのモデルファイルになります。

app/models/user_purchase_history.rb

class UserPurchaseHistory
  include ActiveModel::Model
  attr_accessor :nickname, :email, :encrypted_password, :first_name, :family_name, :first_name_kana, :family_name_kana, :birth_day

  with_options presence: true do
    validates :nickname
    validates :email
    validates :password, format: { with: /\A[a-zA-Z0-9]+\z/, message: "Include both letters and numbers."}
    validates :first_name, format: { with: /\A[ぁ-んァ-ン一-龥]/, message: "Full-width characters."}
    validates :first_name_kana, format: { with: /\A[ァ-ヶー－]+\z/, message: "Full-width katakana characters."}
    validates :family_name, format: { with: /\A[ぁ-んァ-ン一-龥]/, message: "Full-width characters."}
    validates :family_name_kana, format: { with: /\A[ァ-ヶー－]+\z/, message: "Full-width katakana characters."}
    validates :birth_day
  end

  def save
    user =  User.create(nickname: nickname, email: email, password: password, first_name: first_name, family_name: family_name, first_name_kana: first_name_kana, family_name_kana: family_name_kana, birth_day: birth_day)
    SendingDestination.create(post_code: post_code, prefecture_id: prefecture.id, city: city, house_number: house_number, building_name: building_name, phone_number: phone_number, purchase_history_id: purchase_history.id)
    Purchase_history.create(user_id: user.id, item_id: item.id)
  end

end