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Accepted
Hector Hernandez
Asked: 2020-06-23 10:07:55 +0800 CST 2020-06-23 10:07:55 +0800 CST

Sum all rails inventory transactions

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I am creating an inventory system, in which I have the following 2 models:

Model Product

class CreateProducts < ActiveRecord::Migration[5.2]
  def change
    create_table :products do |t|
      t.string :name
      t.float :price
      t.integer :weight
      t.string :unity

      t.timestamps
    end
  end
end

Inventory Transactions Model This registers the amount of items to enter or leave the inventory for each product, for this I have added a boolean field, which will determine the type of transaction, whether it is purchase or sale

class CreateInventoryTransactions < ActiveRecord::Migration[5.2]
  def change
    create_table :inventory_transactions do |t|
      t.string :invoice
      t.integer :product_id
      t.integer :quantity
      t.boolean :transaction_type

      t.timestamps
    end
  end
end

In this case I have made a purchase transaction of 100 items of the same product, but when trying to print that data of that product in the loop, it generates an error, and obviously since that product has many purchase transactions or sale, how could I print the sum of purchase or sale transactions within the loop, for each product?

<% @products.each do |product| %>
  <tr>
    <td>-</td>
    <td><%= product.name %></td>
    <td><%= product.price %></td>
    <td><%= product.weight %></td>
    <td><%= product.unity %></td>
    <td><%= product.inventory_transactions.quantity %></td>
  </tr>
<% end %>

Avoiding the error of:undefined method 'quantity' for #<InventoryTransaction::ActiveRecord_Associations_CollectionProxy:0x007fdc3d68c038>

ruby-on-rails

1 Answers

  1. Best Answer

    The problem is that you are calling the method quantityon a collection, not on an object Product.

    What you have to do is first add the amounts of each transaction and then show them; for instance:

    product.inventory_transactions.sum(&:quantity)

    Although you can use it like this directly in your view, I recommend extracting that logic and adding it in the model Product:

    class Product
  # ...

  def inventory_transactions_quantity
    inventory_transactions.sum(&:quantity)
  end
end

    And in your view you can call the new method:

    product.inventory_transactions_quantity

    ...when making a transaction, I specify it through a boolean field , that is, transaction_typehow could I subtract the amount of purchase data, that is, that they have transaction_type: true, minus the amount of transaction_type: false?

    You could add a (private) method in your model to add the values ​​of quantityfor each transaction_typeand then use it in your current method to get the difference; for instance:

    # app/models/product.rb

class Product < ApplicationRecord
  # ...

  def inventory_transactions_quantity
    transactions_type_quantity(true) - transactions_type_quantity(false)
  end

  private
  def transactions_type_quantity(type)
    inventory_transactions.where(transaction_type: type).sum(&:quantity)
  end
end

    As an exercise to improve this code, you might consider using scopes on the model InventoryTransactionto avoid using wherewithin the model Product.

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