如何在Rasa中实现对话启动阶段统一返回欢迎消息（解决规则与故事冲突问题）

Hey there! Let's tackle this Rasa problem you're facing: you want to send a welcome message no matter what the user sends to kick off a conversation, but your initial rule clashed with existing stories, and you can't define intents for every possible user input. Here are a few practical, actionable solutions:

1. Use a Wildcard Rule + Adjust Policy Priority #

This is the simplest approach—we'll create a rule that matches any user intent when the conversation starts, then set the rule policy to take priority over stories.

First, update your rules file with this wildcard rule:

rule: Greet on Conversation Start
conversation_start: true
steps:
  - intent: *  # Matches ANY user intent (including nlu_fallback for unrecognized inputs)
  - action: utter_greet

Next, fix the rule-story conflict by boosting the RulePolicy priority in your config.yml. Rules will now take precedence over memorized stories:

policies:
  - name: RulePolicy
    priority: 2  # Higher than MemoizationPolicy's default priority of 1
  - name: MemoizationPolicy
  - name: TEDPolicy

This way, the first message from the user—whether it's a product price question, random text, or unrecognized input—will trigger the welcome message first.

2. Custom Action for First Message Handling #

If you want more control (like sending the greeting and processing the user's request in one step), use a custom action. This avoids rule conflicts entirely and lets you handle edge cases easily.

First, add this custom action to your actions.py:

from typing import Any, Text, Dict, List
from rasa_sdk import Action, Tracker
from rasa_sdk.executor import CollectingDispatcher

class ActionHandleFirstMessage(Action):
    def name(self) -> Text:
        return "action_handle_first_message"

    def run(self, dispatcher: CollectingDispatcher,
            tracker: Tracker,
            domain: Dict[Text, Any]) -> List[Dict[Text, Any]]:
        # Send the welcome message first
        dispatcher.utter_message(response="utter_greet")
        
        # Now process the user's actual request
        latest_intent = tracker.latest_message["intent"]["name"]
        if latest_intent == "product_price":
            dispatcher.utter_message(response="utter_product_price")
        # Add more intent-handling logic here for other use cases
        # elif latest_intent == "some_other_intent":
        #     dispatcher.utter_message(response="utter_some_response")
        
        return []

Then update your rule to trigger this custom action for any starting intent:

rule: Handle First User Message
conversation_start: true
steps:
  - intent: *
  - action: action_handle_first_message

3. Auto-Greet on Session Start (Before User Messages) #

If you want to send the welcome message as soon as the conversation starts (before the user even types anything), use a custom ActionSessionStart:

Add this to actions.py:

from rasa_sdk.actions.action import ActionSessionStart
from rasa_sdk.events import SessionStarted

class CustomSessionStart(ActionSessionStart):
    def name(self) -> Text:
        return "action_session_start"

    async def run(
        self,
        dispatcher: CollectingDispatcher,
        tracker: Tracker,
        domain: Dict[Text, Any],
    ) -> List[Dict[Text, Any]]:
        # Send welcome message immediately when session starts
        dispatcher.utter_message(response="utter_greet")
        
        # Run the default session start logic
        events = await super().run(dispatcher, tracker, domain)
        return events

Make sure to register this action in your domain.yml under actions:, and it will fire automatically when a new conversation begins.

Quick Note on Rule-Story Conflicts #

The core issue with your original rule was that it only matched one specific intent (product_price), and your existing stories probably had a flow where that intent triggered a different action. Using the wildcard intent: * combined with a higher rule priority ensures your welcome message rule takes precedence every time a conversation starts.

内容的提问来源于stack exchange，提问作者LLB