How to sum in rails a number of purchases of only one buyer?

Question

I'm building an e-commerce website. In the buyer profile view(users/show.html.erb), i'm try to sum his number of purchases. But i don't know how.

Here is my code:

views/users/show.html.erb:

<h2><%= @user.first_name %> <%= @user.last_name %></h2>

<p>
  <strong>Number of purchases:</strong>
  <% Sale.where(user_id: @user.id).each do |sale| %>
  <%#= sale.product.sum(:id) %>
  <% end %>

</p>


<h4>Products purchased by <%= @user.first_name + " " + @user.last_name%></h4>

<table class="table table-bordered table-hover">
  <thead>
    <tr>
      <th>Name</th>
      <th>Description</th>
      <th>Price</th>
      <th>Image</th>
    </tr>
  </thead>

  <tbody>
    <% Sale.where(user_id: @user.id).each do |sale| %>
    <tr>
      <td><%= sale.product.title %></td>
      <td><%= sale.product.description %></td>
      <td><%= sale.product.price %></td>
      <td>
        <%= link_to image_tag(sale.product.image, :alt => sale.product.title, class:"img-responsive", style:'width: 100px; height: 100px;'), '/products/' + sale.product.id.to_s %> 
      </td>
     </tr>
     <% end %>
    </tbody>
  </table>

db/schema.rb:

create_table "sales", force: :cascade do |t|
t.integer  "product_id"
t.integer  "user_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end

add_index "sales", ["product_id"], name: "index_sales_on_product_id"
add_index "sales", ["user_id"], name: "index_sales_on_user_id"

sales_controller.rb :

class SalesController < ApplicationController
before_action :set_sale, only: [:show, :edit, :update, :destroy]
before_filter :require_user
before_action :require_admin, only: [:index]


# GET /sales
# GET /sales.json
def index
 @sales = Sale.all
end

# GET /sales/1
# GET /sales/1.json
def show
end

# GET /sales/new
def new
 @sale = Sale.new
end

# GET /sales/1/edit
def edit
end

# POST /sales
# POST /sales.json
def create
@sale = Sale.new(sale_params)
@sale.product_id = params[:product_id]
@sale.user_id = current_user.id
@user = @sale.user

 respond_to do |format|
    if @sale.save
     @user.save
     format.html { redirect_to '/', notice: 'Your purchase has been registered !' }
     format.json { render :show, status: :created, location: @sale }
    else
     format.html { render :new }
     format.json { render json: @sale.errors, status: :unprocessable_entity }
    end
   end
 end

private
# Use callbacks to share common setup or constraints between actions.
def set_sale
 @sale = Sale.find(params[:id])
end

# Never trust parameters from the scary internet, only allow the white list through.
def sale_params
 params.permit(:product_id, :user_id)
 end
end
end

Answer 1

First, of all, I would recommend calculating the total number of purchases in the controller and saving it as an instance variable, then simply displaying that variable in the show view. However, if you have some reason for doing the calculation inside the erb file, you can do it simply like this:

    <%= Sale.where(user_id: @user.id).count %>

Answer 2

How about this? <% @user.sales.count %>