How CML Fits in the Product Configure Business API Pipeline

When you call the Product Configure Business API, the request runs through a fixed sequence of stages. The CML constraint engine is one stage in that sequence, and where it runs determines which data it can see.

A single Product Configure Business API call processes the stages in this order.

The Product Configure Business API receives the request.
The CML constraint engine evaluates the configuration and enforces the constraint model.
Pricing procedures calculate prices.
Apex triggers run.
The API returns the response.

Because the constraint engine runs before pricing procedures and Apex triggers, CML can’t read any value that those later stages produce in the same API call. Values calculated by pricing, such as NetUnitPrice, and rollups or fields populated by Apex triggers, aren’t available to CML during that call. If a constraint or external variable references one of these values, it reads whatever was in the context before the call, which is typically a stale value from a previous call or null on the first call.

In this example, GeneratorSet declares an external variable bound to the pricing-computed NetUnitPrice line item field, and a rule that tries to react to it.

1type GeneratorSet {
2    int requiredKW = [101..10000];
3    relation Accessories : Accessory[1..99];
4
5    // Binds to the pricing-computed NetUnitPrice line item field.
6    @(tagName = "NetUnitPrice")
7    extern decimal(2) NetUnitPrice = 0;
8
9    /**
10    * @Title Price-Based Accessory Recommendation
11    * Attempts to recommend 2 accessories when the net unit price
12    * exceeds 5000. This does NOT work as intended.
13    */
14    setdefault(
15        NetUnitPrice > 5000,
16        Accessories[Accessory] == 2,
17        "2 accessories are recommended for high-value generator sets"
18    );
19}

On the first Product Configure Business API call, pricing procedures haven’t run yet when the constraint engine evaluates the model, so NetUnitPrice has no calculated value. The NetUnitPrice external variable falls back to its default of 0 (or is null if no default is set), the condition NetUnitPrice > 5000 is false, and the rule never fires. On a later call, NetUnitPrice reflects the price from the previous call rather than the current configuration, so the rule reacts to a stale value. In either case, the rule can’t reliably respond to the current price, because the price for the current configuration isn’t computed until after the constraint engine finishes.

To make calculated values such as NetUnitPrice or rollup totals available to CML, split the work into two passes and let pricing run in between. The first pass produces a configuration, a separate pricing call calculates and stamps the values onto the transaction, and the second configuration pass reads those values.

Call the Product Configurator Business API, and capture the product bundle line configuration returned in the JSON payload. The payload holds the configuration state, which is the selected products, quantities, attribute values, and line item structure. You reuse this payload to preserve the configuration in the second call.
Invoke the Pricing Business API to let pricing run. Make a POST request to the Pricing Business API, passing the line items from the configuration you captured. This call runs the pricing procedures and any pricing-related Apex triggers to completion, so that final prices, taxes, and discounts are computed and committed to the transaction state.
Extract the calculated pricing values, such as NetUnitPrice, total amounts, or custom rollup fields, from the Pricing Business API response. Map those values into the external variables or context parameters that the CML model reads. These values are separate from the configuration payload, so you add them to the state yourself.
Call the Product Configurator Business API a second time. Pass the configuration state together with the pricing values. On this pass, CML reads the calculated prices instead of null or stale values, so it evaluates your price-dependent constraints and hide or show rules correctly.

For the GeneratorSet example, the NetUnitPrice external variable returns 0 on the first pass. After the Pricing Business API runs and you map the result back, the second pass with the Product Configurator Business API reads the updated NetUnitPrice, so the setdefault rule fires as intended.

For more information, see Product Configurator Business APIs and Salesforce Pricing Business APIs.