How to validate user input without Form

Rasa Open Source
1

User: I want to buy a car

Bot: What car would you like to buy (Sedan or SUV)

User: Honda

Bot: Thank you for choosing {carname}

slots:
  carname:
    type: text
    mappings:
    - type: from_entity
      entity: car_type

How can I validate the car type other than SUV or Sedan. if the user input is Honda then I want to re-prompt and say “Please select a valid option to set the car type”. Here I am looking a solution without form validation is it possible in RASA.

I am referring documentation but not sure how to implement Slot Validation Actions

Please help me.

2

I tried with custom action but it is working only the case of valid entities as a car type.

I wanted to know what would be the right approach to handle this problem.

- intent: car_type
  examples: |
    - [Sedan](car_type)
    - [SUV](car_type)

- story: buy car 
  steps:
  - intent: buy_car
  - action: utter_carbuy
  - intent: car_type
    entities:
    - car_type : SUV
  - action: action_hello_world
  - action: utter_carThankyou