Apply business logic in Common Data Service for Apps
Define business rules for an entity that apply to all the entity forms and at the server level. Business rules defined for an entity apply to both canvas apps and model-driven apps if the entity is used in the app. More information: Create a business rule for an entity
To define a business rule that applies to a form in a model-driven app, see Create business rules for a model-driven app form
You can also use the classic Common Data Service (CDS) for Apps processes, which are workflows and actions. More information: Microsoft Flow: Use Workflow processes and Microsoft Flow: Actions overview.