# Forms

Note

There is an in-depth tutorial [here](https://blog.rasa.com/building-contextual-assistants-with-rasa-formaction/) about how to use Rasa Forms for slot filling.

## [Configuration File](https://legacy-docs-v1.rasa.com/1.7.2/core/forms/#configuration-file)
To use forms, you also need to include the `FormPolicy` in your policy configuration file. For example:

```
policies:
  - name: "FormPolicy"
```

## [Form Basics](https://legacy-docs-v1.rasa.com/1.7.2/core/forms/#form-basics)
Using a `FormAction`, you can describe _all_ of the happy paths with a single story. By “happy path”, we mean that whenever you ask a user for some information, they respond with the information you asked for.

```
## happy path
* request_restaurant
    - restaurant_form
    - form{"name": "restaurant_form"}
    - form{"name": null}
```

## [Custom slot mappings](https://legacy-docs-v1.rasa.com/1.7.2/core/forms/#custom-slot-mappings)
If you do not define slot mappings, slots will be only filled by entities with the same name as the slot that are picked up from the user input. Some slots, like `cuisine`, can be picked up using a single entity, but a `FormAction` can also support yes/no questions and free-text input. The `slot_mappings` method defines how to extract slot values from user responses.

```
def slot_mappings(self) -> Dict[Text, Union[Dict, List[Dict]]]:
    return {
        "cuisine": self.from_entity(entity="cuisine", not_intent="chitchat"),
        "num_people": [
            self.from_entity(entity="num_people", intent=["inform", "request_restaurant"]),
            self.from_entity(entity="number"),
        ],
        "outdoor_seating": [
            self.from_entity(entity="seating"),
            self.from_intent(intent="affirm", value=True),
            self.from_intent(intent="deny", value=False),
        ],
        "preferences": [
            self.from_intent(intent="deny", value="no additional preferences"),
            self.from_text(not_intent="affirm"),
        ],
        "feedback": [self.from_entity(entity="feedback"), self.from_text()],
    }
```

## [Validating user input](https://legacy-docs-v1.rasa.com/1.7.2/core/forms/#validating-user-input)
After extracting a slot value from user input, the form will try to validate the value of the slot. By default, validation only checks if the requested slot was successfully extracted from the slot mappings. If you want to add custom validation, for example to check a value against a database, you can do this by writing a helper validation function with the name `validate_{slot-name}`.

```
def validate_cuisine(
    self,
    value: Text,
    dispatcher: CollectingDispatcher,
    tracker: Tracker,
    domain: Dict[Text, Any],
) -> Dict[Text, Any]:
    if value.lower() in self.cuisine_db():
        return {"cuisine": value}
    else:
        dispatcher.utter_message(template="utter_wrong_cuisine")
        return {"cuisine": None}
```

## [Handling unhappy paths](https://legacy-docs-v1.rasa.com/1.7.2/core/forms/#handling-unhappy-paths)
Of course your users will not always respond with the information you ask of them. The way this works with forms is that a form will raise an `ActionExecutionRejection` if the user didn’t provide the requested information. You need to handle events that might cause `ActionExecutionRejection` errors in your stories.

``` 
## chitchat
* request_restaurant
    - restaurant_form
    - form{"name": "restaurant_form"}
* chitchat
    - utter_chitchat
    - restaurant_form
    - form{"name": null}
```

## [The requested_slot slot](https://legacy-docs-v1.rasa.com/1.7.2/core/forms/#the-requested_slot-slot)
The slot `requested_slot` is automatically added to the domain as an unfeaturized slot. If you want to make it featurized, you need to add it to your domain file as a categorical slot.

## Summary
The `FormAction` will only request slots which haven’t already been set. Once all the slots are filled, the `submit()` method is called. The predefined functions help to define how to extract and validate values dynamically.