Choosing a path with @router

A @router method returns a label, and every method listening to that label runs next. It is how a flow takes one path for refunds and another for order status.

Lesson 21's desk treated every ticket the same. A refund and a status question need different handling.

import re

import shop_llm
from crewai.flow.flow import Flow, listen, start
from pydantic import BaseModel


class Ticket(BaseModel):
    message: str = ""
    order_id: str = ""
    reply: str = ""

The state and imports are lesson 21's. The router needs one more import, and the Desk class gets a second decorator.

from crewai.flow.flow import router

class Desk(Flow[Ticket]):
    @start()
    def read_ticket(self):
        found = re.findall(r"\b[A-Z]\d+\b", self.state.message)
        self.state.order_id = found[0] if found else ""

    @router(read_ticket)
    def route(self):
        return "refund" if "refund" in self.state.message.lower() else "status"

    @listen("refund")
    def refund(self):
        self.state.reply = f"A manager will review the refund for {self.state.order_id}."

The mistake shows up when the flow is created, not when the file is read:

desk = Desk()

@router works like @listen, but the method's return value is a label, and @listen("refund") waits for that label. The flow was refused as soon as it was created: the method that listens to "refund" is also called refund, and a method's own name counts as a trigger, so it would run itself forever.

Distinct names

    @listen("refund")
    def hold_refund(self):
        self.state.reply = f"A manager will review the refund for {self.state.order_id}."

    @listen("status")
    def check_status(self):
        self.state.reply = f"Looking into {self.state.order_id}."

The handlers are now hold_refund and check_status, and there is one for each label the router can return.

for message in ["Where is my order A17?", "Please refund order A17."]:
    desk = Desk(suppress_flow_events=True)
    desk.kickoff(inputs={"message": message})
    print(desk.state.reply)

The router returned one label per ticket, and only the method listening to it ran. A label no method listens to ends the flow there, which is easy to do by a typo.

Both tickets take the same two steps first, and split only at the router. The state is what the router reads, and what every method writes to.