magento-module-development

Create a directory under app/code/Vendor/Module containing registration.php with ComponentRegistrar::register() and etc/module.xml declaring the module name and sequence dependencies. Then add your models, configuration, and run bin/magento setup:upgrade to register it.

Use plugins (interceptors) instead of preferences whenever possible. Plugins are composable so multiple modules can modify the same method, while preferences rewrite the entire class and cause conflicts between modules.

Define the table in etc/db_schema.xml using declarative schema with columns, constraints, and indexes, then run bin/magento setup:upgrade. Generate the whitelist file with setup:db-declaration:generate-whitelist to allow future schema changes.

This usually means DI compilation has not run. Execute bin/magento setup:di:compile and bin/magento cache:flush, and verify the PHP namespace exactly matches the directory path under app/code.

Yes, an uncaught exception in an observer can interrupt critical flows like order placement. Wrap observer logic in try/catch, log errors via LoggerInterface, and never re-throw exceptions from the execute() method.

Define routes in etc/webapi.xml mapping URLs to your repository interface methods, and bind the interface to its implementation with a preference in di.xml. The service class attribute must reference the interface, not a concrete class.