How is data validation implemented in Mendix applications?

Data validation in Mendix applications is primarily implemented by using validation rules defined in the domain model. This approach allows developers to establish criteria that must be met for data to be considered valid before it can be saved to the database. These rules can include checks for required fields, data type constraints, and custom validation logic, ensuring that the integrity and consistency of the data is maintained systematically throughout the application.

Using validation rules is beneficial because it centralizes the validation logic within the domain model, making it easier to manage and modify as the application evolves. This also helps to enforce business logic consistently across different parts of the application, reducing the chances of data errors and improving overall reliability.

The other options reflect practices that could complement data validation but do not provide the systematic approach offered by validation rules within the domain model. For instance, relying on manual checks by developers can introduce human error and inconsistency, while user feedback at runtime is typically reactive rather than proactive in ensuring data validity. Limiting data input to numerical values only might be valid in specific contexts, but it doesn’t encompass the full spectrum of validations that a robust application must enforce.