On a scheduled basis, the pricing engines load global promotions (those defined as applying automatically to all customers). An engine builds its list by using its globalPromotionsQuery property to query the Promotions repository, searching for any promotion where the Automatically Give to All Customers (global) property is set to true. Each engine loads the global promotions that are specific to that pricing engine; for example, the ItemPricingEngine loads the global Item Discount promotions.

At the start of the customer session, a PricingModelHolder instance is created. PricingModelHolder calls each pricing engine’s getPricingModels() method.

The pricing engine getPricingModels() method gets any promotions listed in the activePromotions property of the current customer’s profile and merges them with the global promotions list it previously created. The pricing engine can also veto promotions from being returned to the PricingModelHolder at this point.

PricingModelHolder periodically updates both the global and active promotions.

The business layer logic (such as a PriceItem servlet bean in a page) invokes a pricing engine (see The Base Pricing Engine).

The pricing operation invokes PricingTools which then gets the PricingModelHolder for that customer.

PricingTools gets the promotions from the PricingModelHolder and calls the pricing engine’s priceItems method, passing in the promotions as a list.

The pricing engine applies its configured precalculators in the order in which they appear in its preCalculators property. A precalculator modifies a price without using any associated promotions. For example, a site could use a list price precalculator or an order subtotal precalculator to establish a base price to which subsequent calculators then apply a discount.

Each type of engine calls its corresponding type of precalculator – for example, the OrderPricingEngineImpl calls OrderPricingCalculators and the TaxPricingEngineImpl calls TaxPricingCalculators.

The pricing engine then takes the promotions list that was passed in and can again veto promotions from that list. The remaining promotions are sorted by priority and then evaluated.

Each promotion contains a PMDL rule that describes the discount. For example, a rule might define a discount in which a customer buys one item and receives a second for free. The PMDL specifies the calculator type to use to determine the amount of the discount in the calculator-type attribute of the discount-structure element. The calculator type maps to a calculator component in the calculatorTypeCalculators map.

For each available promotion, Commerce does the following:

The pricing engine applies its configured PostCalculators, which make any necessary modifications to the price after discounts have been applied. Each pricing engine calls postcalculators of its own type.

The pricing engine returns an updated PriceInfo object.