mirror of
https://github.com/langchain-ai/langgraph.git
synced 2026-08-22 15:42:25 +02:00
feat: add an append only mode to add messages reducer
This commit is contained in:
Josh Rogers
@@ -63,6 +63,7 @@ def add_messages(
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right: Messages,
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*,
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format: Literal["langchain-openai"] | None = None,
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mode: Literal["allow_everything", "append_only"] = "allow_everything",
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) -> Messages:
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"""Merges two lists of messages, updating existing messages by ID.
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@@ -83,10 +84,19 @@ def add_messages(
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Must have `langchain-core>=0.3.11` installed to use this feature.
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mode: Controls how message updates and removals are handled. Options are:
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- `allow_everything` (default): Allows adding new messages, updating
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existing messages by ID, and removing messages. This is the standard behavior.
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- `append_only`: Only allows adding new messages. If a message in `right`
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has the same ID as a message in `left` (update or removal), a `ValueError`
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will be raised. This mode is useful when you want to prevent any modification
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of message history.
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Returns:
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A new list of messages with the messages from `right` merged into `left`.
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If a message in `right` has the same ID as a message in `left`, the
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message from `right` will replace the message from `left`.
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message from `right` will replace the message from `left` (in
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`allow_everything` mode) or raise a `ValueError` (in `append_only` mode).
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Example: Basic usage
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```python
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@@ -183,6 +193,30 @@ def add_messages(
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# }
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```
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Example: Use append_only mode to prevent message updates
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```python
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from typing import Annotated
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from typing_extensions import TypedDict
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from langgraph.graph import StateGraph, add_messages
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class State(TypedDict):
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messages: Annotated[list, add_messages(mode="append_only")]
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# This will work - adding new messages
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msgs1 = [HumanMessage(content="Hello", id="1")]
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msgs2 = [AIMessage(content="Hi there!", id="2")]
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add_messages(msgs1, msgs2, mode="append_only")
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# [HumanMessage(content='Hello', id='1'), AIMessage(content='Hi there!', id='2')]
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# This will raise an error - trying to update an existing message
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msgs1 = [HumanMessage(content="Hello", id="1")]
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msgs2 = [HumanMessage(content="Hello again", id="1")]
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add_messages(msgs1, msgs2, mode="append_only")
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# ValueError: Cannot update existing message with ID '1' in append_only mode
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```
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"""
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remove_all_idx = None
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# coerce to list
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@@ -207,6 +241,11 @@ def add_messages(
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if m.id is None:
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m.id = str(uuid.uuid4())
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if isinstance(m, RemoveMessage) and m.id == REMOVE_ALL_MESSAGES:
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if mode == "append_only":
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raise ValueError(
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"Cannot remove all messages in append_only mode. "
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"Use mode='allow_everything' to allow message removal."
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)
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remove_all_idx = idx
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if remove_all_idx is not None:
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@@ -218,6 +257,18 @@ def add_messages(
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ids_to_remove = set()
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for m in right:
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if (existing_idx := merged_by_id.get(m.id)) is not None:
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# Check for append_only mode violation
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if mode == "append_only":
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if isinstance(m, RemoveMessage):
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raise ValueError(
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f"Cannot remove existing message with ID '{m.id}' in append_only mode. "
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f"Use mode='allow_everything' to allow message removal."
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)
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else:
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raise ValueError(
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f"Cannot update existing message with ID '{m.id}' in append_only mode. "
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f"Use mode='allow_everything' to allow message updates."
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)
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if isinstance(m, RemoveMessage):
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ids_to_remove.add(m.id)
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else:
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@@ -367,3 +367,139 @@ def test_push_messages_in_graph():
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messages.append(message)
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assert values["messages"] == messages
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def test_append_only_mode_allows_new_messages():
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"""Test that append_only mode allows adding new messages."""
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left = [HumanMessage(content="Hello", id="1")]
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right = [AIMessage(content="Hi there!", id="2")]
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result = add_messages(left, right, mode="append_only")
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expected = [
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HumanMessage(content="Hello", id="1"),
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AIMessage(content="Hi there!", id="2"),
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]
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assert result == expected
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def test_append_only_mode_prevents_updates():
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"""Test that append_only mode raises an error when trying to update an existing message."""
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left = [HumanMessage(content="Hello", id="1")]
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right = [HumanMessage(content="Hello again", id="1")]
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with pytest.raises(
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ValueError,
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match="Cannot update existing message with ID '1' in append_only mode",
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):
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add_messages(left, right, mode="append_only")
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def test_append_only_mode_prevents_remove_messages():
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"""Test that append_only mode prevents RemoveMessage operations."""
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left = [
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HumanMessage(content="Hello", id="1"),
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AIMessage(content="Hi there!", id="2"),
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]
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right = [RemoveMessage(id="2")]
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with pytest.raises(
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ValueError,
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match="Cannot remove existing message with ID '2' in append_only mode",
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):
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add_messages(left, right, mode="append_only")
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def test_append_only_mode_prevents_remove_all_messages():
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"""Test that append_only mode prevents REMOVE_ALL_MESSAGES operations."""
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left = [
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HumanMessage(content="Hello", id="1"),
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AIMessage(content="Hi there!", id="2"),
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]
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right = [RemoveMessage(id=REMOVE_ALL_MESSAGES)]
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with pytest.raises(
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ValueError,
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match="Cannot remove all messages in append_only mode",
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):
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add_messages(left, right, mode="append_only")
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def test_append_only_mode_with_multiple_new_messages():
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"""Test that append_only mode allows adding multiple new messages."""
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left = [HumanMessage(content="Hello", id="1")]
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right = [
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AIMessage(content="Hi there!", id="2"),
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SystemMessage(content="System message", id="3"),
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HumanMessage(content="Another message", id="4"),
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]
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result = add_messages(left, right, mode="append_only")
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expected = [
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HumanMessage(content="Hello", id="1"),
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AIMessage(content="Hi there!", id="2"),
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SystemMessage(content="System message", id="3"),
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HumanMessage(content="Another message", id="4"),
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]
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assert result == expected
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def test_append_only_mode_with_mixed_operations():
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"""Test that append_only mode fails when mixing new messages with updates."""
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left = [HumanMessage(content="Hello", id="1")]
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right = [
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AIMessage(content="Hi there!", id="2"), # new message
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HumanMessage(content="Updated hello", id="1"), # update attempt
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]
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with pytest.raises(
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ValueError,
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match="Cannot update existing message with ID '1' in append_only mode",
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):
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add_messages(left, right, mode="append_only")
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def test_allow_everything_mode_default_behavior():
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"""Test that allow_everything mode is the default and allows updates."""
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left = [HumanMessage(content="Hello", id="1")]
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right = [HumanMessage(content="Hello again", id="1")]
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# Test without specifying mode (should default to allow_everything)
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result = add_messages(left, right)
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expected = [HumanMessage(content="Hello again", id="1")]
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assert result == expected
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# Test with explicit mode
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result = add_messages(left, right, mode="allow_everything")
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assert result == expected
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def test_append_only_mode_in_state_graph():
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"""Test append_only mode works correctly in a StateGraph."""
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class State(TypedDict):
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messages: Annotated[list[AnyMessage], add_messages(mode="append_only")]
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def add_message(state: State):
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return {"messages": [AIMessage(content="Response", id="2")]}
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def try_update_message(state: State):
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# This should fail because message with id="1" already exists
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return {"messages": [HumanMessage(content="Updated", id="1")]}
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# Test successful case
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builder = StateGraph(State)
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builder.add_node("add_message", add_message)
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builder.add_edge(START, "add_message")
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builder.add_edge("add_message", END)
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graph = builder.compile()
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result = graph.invoke({"messages": [HumanMessage(content="Hello", id="1")]})
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assert len(result["messages"]) == 2
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assert result["messages"][0].content == "Hello"
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assert result["messages"][1].content == "Response"
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# Test failure case
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builder2 = StateGraph(State)
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builder2.add_node("try_update", try_update_message)
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builder2.add_edge(START, "try_update")
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builder2.add_edge("try_update", END)
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graph2 = builder2.compile()
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with pytest.raises(
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ValueError,
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match="Cannot update existing message with ID '1' in append_only mode",
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):
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graph2.invoke({"messages": [HumanMessage(content="Hello", id="1")]})
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