FastAPI ViewSet Lifecycle Hooks: Advanced API Object Processing

FastAPI Mason ViewSets support lifecycle hooks that let you customize object processing at key stages. Control validation, before and after save operations, and implement custom create or update logic to tailor your API behavior precisely.

Method	When it is called
validate_data	Before processing input data (create/update)
before_save	Before saving the object (create/update)
after_save	After saving the object (create/update)
perform_create	When creating an object (POST)
perform_update	When updating an object (PUT/PATCH)
perform_destroy	When deleting an object (DELETE)

You can override any of these methods in your ViewSet to add custom logic. Example:

@viewset(router)
class CompanyViewSet(ModelViewSet[Company]):
    # ...
    async def validate_data(self, data: CompanyCreateSchema):
        return data

    async def before_save(self, obj: Company):
        pass

    async def after_save(self, obj: Company):
        pass

    async def perform_create(self, obj: Company):
        await obj.save()
        return obj

    async def perform_update(self, obj: Company):
        await obj.save()
        return obj

    async def perform_destroy(self, obj: Company):
        obj.is_deleted = True
        await obj.save()

Call order for create/update:

1. validate_data
2. before_save
3. perform_create / perform_update
4. after_save

For deletion, only perform_destroy is called.