docs: update chain migration guide (#24501)

- Update `ConversationChain` example to show use without session IDs;
- Fix a minor bug (specify history_messages_key).

docs/docs/how_to/migrate_chains.ipynb

@@ -284,17 +284,17 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 8,
+   "execution_count": 1,
    "id": "173e1a9c-2a18-4669-b0de-136f39197786",
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "\"Arr, matey! I be sailin' the high seas with me crew, searchin' for buried treasure and adventure! How be ye doin' on this fine day?\""
+       "\"Arrr, I be doin' well, me heartie! Just sailin' the high seas in search of treasure and adventure. How be ye?\""
       ]
      },
-     "execution_count": 8,
+     "execution_count": 1,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -316,14 +316,20 @@
     "\n",
     "history = InMemoryChatMessageHistory()\n",
     "\n",
+    "\n",
+    "def get_history():\n",
+    "    return history\n",
+    "\n",
+    "\n",
     "chain = prompt | ChatOpenAI() | StrOutputParser()\n",
     "\n",
-    "wrapped_chain = RunnableWithMessageHistory(chain, lambda x: history)\n",
+    "wrapped_chain = RunnableWithMessageHistory(\n",
+    "    chain,\n",
+    "    get_history,\n",
+    "    history_messages_key=\"chat_history\",\n",
+    ")\n",
     "\n",
-    "wrapped_chain.invoke(\n",
-    "    {\"input\": \"how are you?\"},\n",
-    "    config={\"configurable\": {\"session_id\": \"42\"}},\n",
-    ")"
+    "wrapped_chain.invoke({\"input\": \"how are you?\"})"
    ]
   },
   {
@@ -340,17 +346,17 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 7,
+   "execution_count": 2,
    "id": "4e05994f-1fbc-4699-bf2e-62cb0e4deeb8",
    "metadata": {},
    "outputs": [
     {
      "data": {
       "text/plain": [
-       "AIMessage(content=\"Ahoy there! What be ye wantin' from this old pirate?\", response_metadata={'token_usage': {'completion_tokens': 15, 'prompt_tokens': 29, 'total_tokens': 44}, 'model_name': 'gpt-3.5-turbo-0125', 'system_fingerprint': None, 'finish_reason': 'stop', 'logprobs': None}, id='run-1846d5f5-0dda-43b6-bb49-864e541f9c29-0', usage_metadata={'input_tokens': 29, 'output_tokens': 15, 'total_tokens': 44})"
+       "'Ahoy matey! What can this old pirate do for ye today?'"
       ]
      },
-     "execution_count": 7,
+     "execution_count": 2,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -370,9 +376,16 @@
     "\n",
     "chain = prompt | ChatOpenAI() | StrOutputParser()\n",
     "\n",
-    "wrapped_chain = RunnableWithMessageHistory(chain, get_session_history)\n",
+    "wrapped_chain = RunnableWithMessageHistory(\n",
+    "    chain,\n",
+    "    get_session_history,\n",
+    "    history_messages_key=\"chat_history\",\n",
+    ")\n",
     "\n",
-    "wrapped_chain.invoke(\"Hello!\", config={\"configurable\": {\"session_id\": \"abc123\"}})"
+    "wrapped_chain.invoke(\n",
+    "    {\"input\": \"Hello!\"},\n",
+    "    config={\"configurable\": {\"session_id\": \"abc123\"}},\n",
+    ")"
    ]
   },
   {
@@ -790,7 +803,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.10.5"
+   "version": "3.10.4"
   }
  },
  "nbformat": 4,