Variant Price Surcharge: Technical Details

Technical details of Variant Price Surcharge: storefront and cart flow, plugin structure, services and tags, logging, error code, plus notes on extensibility, permissions and snippets.

Deutsche Version

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Technical Details

Flow

graph TD
    A["Product loaded in sales channel"] --> B["ProductSubscriber"]
    B --> C["SurchargeConfigReader"]
    C --> D["ParentPriceResolver"]
    D --> E["VariantPriceCalculator"]
    E --> F["QuantityPriceCalculator"]
    F --> G["calculatedPrice of the variant"]
    H["Cart is calculated"] --> I["VariantPriceProcessor"]
    I --> C
    I --> D
    I --> E
    I --> F
    F --> J["Price of the line item"]

Plugin structure

Class	Purpose
`MmdVariantPriceSurcharge`	Plugin class. On uninstall without "keep user data" it deletes the custom field set and system configuration.
`Migration1705200000CreateCustomFields`	Creates the custom field set and the three fields
`Subscriber\ProductSubscriber`	Listens to `sales_channel.product.loaded` and replaces the calculated price of variants
`Core\Checkout\Cart\VariantPriceProcessor`	Cart processor, service tag `shopware.cart.processor`, priority 1000
`Service\SurchargeConfigReader`	Reads and validates the custom fields, decides on inheritance
`Service\SurchargeConfig`	Immutable value object of percentage and surcharge
`Service\ParentPriceResolver`	Loads the parent product with its advanced prices, determines its price, caches per request
`Service\VariantPriceCalculator`	Calculation, value ranges, rounding settings from the system configuration
`Exception\ParentProductNotFoundException`	HTTP 404, error code `MMD_VARIANT_PRICE_SURCHARGE__PARENT_NOT_FOUND`

Details

The ParentPriceResolver carries the kernel.reset tag and clears its cache between requests.
The rounding settings are read from the system configuration with the sales channel ID.
The cart processor is registered as a public service so it is not removed during container compilation.
The cart processor loads variants and parent products each in a single query for all line items and takes the tax rules from the existing price definition.
Problems are written through the logger: warnings for invalid or non-numeric values and for missing parent products in the cart, errors for missing parent products in the product display.

Extensibility, permissions, snippets

The plugin defines no events, extension points or configuration interfaces of its own. The services are regular Symfony services.
It registers no admin role permissions (ACL), no admin modules and no storefront templates.
It ships no snippet files. The custom field labels (de-DE and en-GB) are stored in the custom field set's configuration, the plugin settings' labels in config.xml.