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Spree extension that allows quantity discounts

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README.md

Simple Volume Pricing

Simple Volume Pricing is an extension to Spree (a complete open source commerce solution for Ruby on Rails) that allows order quantity to determine the price for a particular product variant. For instance the variant's starting price might be $19.99, but $18 if customer orders 5 or more units or $15 if customer orders 20 or more.

Each VolumePrice contains the following values:

  1. Variant: Each VolumePrice is associated with a Variant, which is used to link products to particular prices.
  2. Starting Quantity: The minimum quantity for which this VolumePrice applies. If there is a VolumePrice with higher starting quantity that still applies to this order, it will be used instead.
  3. Price: The price of the variant if the line item quantity is big enough for this VolumePrice to apply.

Variant objects get a new boolean property progressive_volume_discount to select between two available discount strategies.

Product objects get a boolean property variants_use_master_discount that controls whether the volume is calculated per product or separately for each of it's variants.

If you want to see the extension's UI there are screenshots available.

Installation

Currently I do not release this extension as a gem. To use it add this to your Gemfile:

gem "spree_simple_volume_pricing", :git => "https://github.com/amw/spree-simple-volume-pricing.git", :tag => "v3.0.0"

Options

Single volume discount for all variants

By default volume discount is configured and calculated separately for all variants. There is a per-product preference that you can use if you want it to be calculated based on the sum of product's variants in the cart. This implies that the starting price and volume prices that were set for particular variants will be ignored and, instead, the product's own pricing scheme will be used.

Uniform vs Progressive volume discount

This extension supports two discount strategies. Uniform volume discount selects one VolumePrice based on ordered quantity and applies it to all ordered units. Progressive volume discount applies different VolumePrices to different portions of the item's quantity. This means that you can charge i.e. $15 for the first three units in the cart, $13 for the next five and $10 for all additional.

Some people find progressive volume discount easier to configure. With prices applied uniformly your customers often end up in situations when it's cheaper to buy X + Y units than just X (a substantial price drop can neglect an added quantity).

Uniform Volume Discount examples

Rails T-Shirt variant has a price of $19.99. Consider the following examples of volume prices:

   Variant             Starting Quantity  Price
   ---------------------------------------------
   Rails T-Shirt       5                  18.00
   Rails T-Shirt       20                 15.00

Example 1

Cart Contents:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          1              19.99       19.99

Order details:

   Subtotal:           19.99

Example 2

Cart Contents:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          5              19.99       99.95

Order details:

   Volume Discount:    -9.95 # 5 * (19.99 - 18.00)
   Subtotal:           90.00 # 5 * 18.00

Example 3

Cart Contents:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          6              19.99       119.94

Order details:

   Volume Discount:   -11.94 # 6 * (19.99 - 18.00)
   Subtotal:          108.00 # 6 * 18.00

Example 4

Cart Contents:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          20             19.99       399.80

Order details:

   Volume Discount:   -99.80 # 20 * (19.99 - 15.00)
   Subtotal:          300.00 # 20 * 15.00

Progressive Volume Discount examples

Given the same volume prices configuration as in uniform discount examples.

Example 1

Cart Contents:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          6              19.99       119.94

Order details:

   Volume Discount:    -3.98
   Subtotal:          115.96 # 4 * 19.99 + 2 * 18.00

Example 2

Cart Contents:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          25             19.99       499.75

Order details:

   Volume Discount:   -59.79
   Subtotal:          439.96 # 4 * 19.99 + 15 * 18.00 + 6 * 15.00

Why is it simple

This extension is called Simple to differentiate it from another volume pricing extension created and maintained by the Spree Core team at RailsDog.

Simple Volume Pricing is simple to use, but gives you the same level of control. It doesn't require you to define ranges, assign them a human readable description or arrange them in order manually. You just slice the quantity continuum with points (starting quantity) between 1 and infinity. The volume price with highest starting quantity is automatically open ended. If you need to end that range just add another point with the variant's original price.

The original extension had also some issues, such as defining overlapping ranges. The models were unnecessarily complicated. Why acts_as_list if you can just order volume prices by their lower quantity range end?

Volume Customers

By default volume prices are calculated based only on the quantity of the current order. But your business might want to allow customers to buy huge volumes over a number of smaller orders. If you want to include quantities from customer's past orders in volume price calculation you can overwrite Order::variant_starting_quantity(variant) method. By default it returns 0.

Example

If you want to calculate customer's volume discount based on his order history from last 31 days just add this to your site's code:

Order.class_eval do
  def variants_starting_quantity *variant_ids
    orders = Order.complete.by_customer(self.email).between(self.created_at - 1.month + 1.day, self.created_at + 1.day)
    orders.map do |o|
      o.line_items.select do |li|
        variant_ids.include? li.variant_id
      end.map(&:quantity).sum
    end.sum
  end
end

Assuming the same volume prices configuration as above and uniform volume discount strategy. First order:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          8              19.99       159.92

Order details:

   Volume Discount:    -15.92 # 8 * (19.99 - 18.00)
   Subtotal:           144.00 # 8 * 18.00

Next order during the next 31 days:

   Product                Quantity       Price       Total
   ----------------------------------------------------------------
   Rails T-Shirt          4              19.99       79.96

Order details:

   Volume Discount:     -7.96 # 4 * (19.99 - 18.00)
   Subtotal:            72.00 # 4 * 18.00

Authors

This extension is based on spree-volume-pricing extension. It was rewritten by Adam Wróbel of Flux Inc, but there are some bits by the original authors in the initial commit.

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