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Small Business: Technical details

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Architecture

graph TD
    A["KleinunternehmerSettings (singleton)"] --> B["NoticeApplicabilityChecker"]
    C["ZeroTaxCategoryProvider"] --> D["ProductPriceMigrationService"]
    D --> E["MigratedProductVariant (tracking table)"]
    B --> F["KleinunternehmerExtension (Twig)"]
    B --> G["ShopNoticeNormalizer (Shop API)"]
    F --> H["Twig hooks: storefront"]
    F --> I["credit_memo.html.twig (refund plugin)"]
    J["Admin: settings page"] --> A
    J --> D
    K["Console: migrate-prices"] --> D

One class decides whether the notice applies: NoticeApplicabilityChecker. Storefront Twig, Shop API and credit memo PDF all ask it, so the three paths always agree.

Plugin structure

src/
├── Command/              # MigrateProductPricesCommand, SetupCommand
├── Controller/Admin/     # KleinunternehmerSettingsController, MigrateProductPricesAction
├── DependencyInjection/  # Extension, Configuration, Compiler/CreditMemoPdfTemplatePass
├── Entity/               # KleinunternehmerSettings, MigratedProductVariant
├── Form/Type/            # KleinunternehmerSettingsType
├── Menu/                 # AdminMenuListener, MenuGroup
├── Migrations/           # three Doctrine migrations
├── Provider/             # ZeroTaxCategoryProvider
├── Repository/           # repositories for both entities
├── Serializer/           # ShopNoticeNormalizer
├── Service/              # NoticeApplicabilityChecker, ProductPriceMigrationService
└── Twig/                 # KleinunternehmerExtension
config/
├── routes/               # admin.yaml (shop.yaml is empty)
├── services/             # service definitions
└── twig_hooks/           # admin_settings.yaml, shop_product_prices.yaml
templates/
├── admin/kleinunternehmer/   # settings page, migration card
├── shop/                     # notice templates (paragraph and table row)
└── refund/                   # credit_memo.html.twig
translations/             # messages and flashes, German and English

The plugin defines no configurable keys (Configuration is empty) and reads no environment variables.

Database

erDiagram
    mmd_kleinunternehmer_settings {
        integer id PK
        boolean active
        text noticeTextDe
        text noticeTextEn
    }
    mmd_kleinunternehmer_migrated_variant {
        integer id PK
        string productVariantCode UK
        string originalTaxCategoryCode
        datetime_immutable migratedAt
    }

The entities are plain Doctrine entities with PHP attributes, not Sylius resources. That is why there is no grid and no CRUD routes.

Three migrations under the namespace Mmd\SyliusKleinunternehmerPlugin\Migrations:

The migrations use Doctrine's Schema API instead of raw SQL so they do not depend on one database platform. The namespace must stay unique in the host application.

How the bundle hooks in

• Doctrine mapping and migrations: The extension registers the ORM mapping for src/Entity/ and the migrations in prepend().
• Twig hooks: The extension also loads the YAML files from config/twig_hooks/ itself in prepend(). It could not do so in load(), because Symfony hands each extension an empty container builder there in which sylius_twig_hooks is never registered.
• Credit memo template: The compiler pass CreditMemoPdfTemplatePass swaps, in the service sylius_refund.generator.credit_memo_pdf_file, the template @SyliusRefundPlugin/download/credit_memo.html.twig (argument 2) for @MmdSyliusKleinunternehmerPlugin/refund/credit_memo.html.twig. The pass does nothing if the refund plugin is missing or the generator already uses another template. It is registered in MmdSyliusKleinunternehmerPlugin::build().
• Admin menu: AdminMenuListener adds the entry under the shared group "MMKreativ Plugins". MenuGroup is deliberately copied into every MMKreativ plugin, only the group code mmd_plugins has to match. Whichever runs first creates the group.
• Admin routes: Both paths build on the parameter sylius_admin.path_name instead of a fixed /admin, so they stay inside the firewall if you change the admin path.

Admin hooks

The settings page renders under the hook prefix sylius_admin.mmd_kleinunternehmer_settings.index and inherits its basic frame (sidebar, navbar, header) from sylius_admin.common.index. The hookables in config/twig_hooks/admin_settings.yaml are activation_error (priority 110), form (100), additional_languages_hint (75) and migration (50) in the content area, as well as title (100) and actions (0) in the title block.

Routes

Tax category and zone

The constants for category and tax rate are kleinunternehmer_zero and kleinunternehmer_zero_rate. The zone DE is hard-coded. This is a deliberate simplification, the zone is not derived dynamically.

Extensibility

The plugin defines no events, service tags or interfaces of its own for third parties. Through normal Symfony service decoration you can replace three public services:

The methods at a glance:

In addition, KleinunternehmerSettingsRepository::getSettings() returns the settings record. If the row is missing, it returns an unsaved default so that a storefront page view never writes.

If you replace NoticeApplicabilityChecker, your decision applies equally to storefront, Shop API and credit memo PDF. Otherwise the plugin hooks in without anything special: AdminMenuListener listens to the Sylius event sylius.menu.admin.main, and ShopNoticeNormalizer is a regular serializer normalizer with priority 60.

Version display

Below the title of the settings page, the installed version is shown (kleinunternehmer_plugin_version(), reads Composer\InstalledVersions). For a tagged release this is the version number, for a local path installation dev-main plus the first seven characters of the commit hash.