上一篇我們已經完成 API 的撰寫了，接下來要把它改寫成 Sub-Agent。

改為 Agent

首先，我們要把原本的 FastAPI 函式改寫成 可被 ADK 調用的 Agent。

1. 匯入模組 與 prompt.py 並建立資料庫

   from fastapi import HTTPException
   from google.adk.agents import Agent
   from . import prompt
   
   HOTEL_DATABASE = {
       "Taipei": [
           {"name": "Taipei Grand Hotel", "stars": 5, "price": 4000},
           {"name": "Hotel Proverbs Taipei", "stars": 4, "price": 3000},
           {"name": "Cosmos Hotel Taipei", "stars": 3, "price": 2000},
           {"name": "Caesar Park Hotel", "stars": 4, "price": 3500},
       ],
       "Tokyo": [
           {"name": "Park Hyatt Tokyo", "stars": 5, "price": 50000},
           {"name": "Shinjuku Granbell Hotel", "stars": 4, "price": 20000},
           {"name": "Hotel Sunroute Plaza", "stars": 3, "price": 15000},
       ],
       "New York": [
           {"name": "The Plaza", "stars": 5, "price": 700},
           {"name": "Pod 51 Hotel", "stars": 3, "price": 200},
           {"name": "Arlo SoHo", "stars": 4, "price": 350},
       ],
   }
   

2. 建立搜尋工具函式
   它可以在資料庫中找到指定的飯店。

   def find_hotel_by_name(name: str):
       for city, hotels in HOTEL_DATABASE.items():
           for hotel in hotels:
               if hotel["name"].lower() == name.lower():
                   return hotel
       return None
   

功能：遍歷所有城市，找到名稱符合的飯店。
找不到就回傳 None。

3. Sub-Agent 的工具函式（Tool Function）
   接著，我們把原本的 API 改成可以被 Agent 調用的「工具函式」。

   def compare_hotels(request: dict) -> dict:
       """
       呼叫飯店比較 Agent，支援「最便宜」或「最佳評價」比較
       """
       try:
           hotel_names = request.get("hotel_names", [])
           criterion = request.get("criterion", "cheapest").lower()
   
           if not hotel_names or len(hotel_names) != 2:
               raise ValueError("Please provide exactly two hotel names in 'hotel_names'.")
   
           hotel1 = find_hotel_by_name(hotel_names[0])
           hotel2 = find_hotel_by_name(hotel_names[1])
   
           if not hotel1 or not hotel2:
               missing = [n for n, h in zip(hotel_names, [hotel1, hotel2]) if h is None]
               raise ValueError(f"Hotel(s) not found in database: {', '.join(missing)}")
   
           if criterion == "cheapest":
               if hotel1["price"] == hotel2["price"]:
                   comparison = f"{hotel1['name']} 與 {hotel2['name']} 價格相同 ({hotel1['price']} = {hotel2['price']})"
                   recommended = hotel1
               else:
                   recommended = min([hotel1, hotel2], key=lambda x: x["price"])
                   worse = hotel2 if recommended == hotel1 else hotel1
                   comparison = f"{recommended['name']} 的價格較便宜 ({recommended['price']} < {worse['price']})"
           elif criterion == "best_rating":
               if hotel1["stars"] == hotel2["stars"]:
                   comparison = f"{hotel1['name']} 與 {hotel2['name']} 評價相同 ({hotel1['stars']}★ = {hotel2['stars']}★)"
                   recommended = hotel1
               else:
                   recommended = max([hotel1, hotel2], key=lambda x: x["stars"])
                   worse = hotel2 if recommended == hotel1 else hotel1
                   comparison = f"{recommended['name']} 評價較高 ({recommended['stars']}★ > {worse['stars']}★)"
           else:
               raise ValueError("Criterion must be 'cheapest' or 'best_rating'.")
   
           return {
               "status": "success",
               "criterion": criterion,
               "hotels_compared": [hotel1, hotel2],
               "comparison_result": comparison,
               "recommended_hotel": recommended,
           }
   
       except Exception as e:
           raise HTTPException(status_code=500, detail=f"An error occurred: {e}")
   

功能摘要：

• 從 request 中取出要比較的兩個飯店名稱與條件（價格或評價）
• 進行比較並回傳結果
• 相同評價時會回傳相同

Sub-Agent

hotel_compare_agent = Agent(
    name="hotel_compare_agent",
    model="gemini-2.5-flash",
    description=prompt.HOTEL_COMPARE_AGENT_DESCRIPTION,
    instruction=prompt.HOTEL_COMPARE_AGENT_INSTRUCTION,
    tools=[compare_hotels],
)

這樣一來，Master Agent（Root Agent）在接收到使用者說：
「請幫我比較 Taipei Grand Hotel 跟 Hotel Proverbs Taipei 哪一個比較便宜」時，就會自動調用這個 hotel_compare_agent。

簡易的 Prompt

Prompt 分成兩個部分：

• description：描述這支 Agent 的任務內容，這裡是「負責比較兩家飯店」。

  HOTEL_COMPARE_AGENT_DESCRIPTION = """
  This is a hotel comparison sub-agent that compares two specified hotels and determines which one is better based on price or rating.
  """
  

• instruction：詳細指令，告訴 Agent 該怎麼做。

  HOTEL_COMPARE_AGENT_INSTRUCTION = """
  You are a hotel comparison agent responsible for analyzing two hotels.
  
  Your responsibilities:
  - Accept exactly two hotel names and a comparison criterion ("cheapest" or "best_rating").
  - Retrieve hotel data from the internal database.
  - Compare the hotels based on the given criterion:
    - "cheapest": select the hotel with the lower price.
    - "best_rating": select the hotel with the higher star rating.
  - If both hotels have the same price or rating, clearly indicate this in your response.
  - Return:
    - hotels_compared: full information of both hotels
    - comparison_result: a textual summary of which hotel is better
    - recommended_hotel: the recommended hotel
  
  Ensure your recommendation is clear, precise, and includes the comparison details.
  """
  

  • prompt 的內容概述

    1. 輸入要求

       • 接收兩個飯店名稱（hotel_names）。
       • 接收比較條件（criterion）：
         • cheapest：比價格（選擇較便宜的飯店）
         • best_rating：比評價（選擇評價較高的飯店）

    2. 執行流程

       • 從內部資料庫抓取兩間飯店資料。
       • 根據條件比較兩者。
       • 若兩間飯店的價格或評價相同，需在結果中清楚說明。

    3. 輸出格式

       • hotels_compared: 兩間飯店的完整資料（名稱、價格、星級）。
       • comparison_result: 文字說明哪一間較好與比較依據。
       • recommended_hotel: 最推薦的飯店資訊。

    4. 語氣與風格

       • 回覆需「清楚」、「具體」、「邏輯明確」。
       • 不得模糊描述或省略比較依據。