feat(langchain_v1): add override to model request and tool call request (#33465)

Add override to model request and tool call request

libs/langchain_v1/langchain/agents/middleware/types.py

@@ -3,7 +3,7 @@
 from __future__ import annotations
 
 from collections.abc import Awaitable, Callable
-from dataclasses import dataclass, field
+from dataclasses import dataclass, field, replace
 from inspect import iscoroutinefunction
 from typing import (
     TYPE_CHECKING,
@@ -30,7 +30,7 @@ from langgraph.channels.untracked_value import UntrackedValue
 from langgraph.graph.message import add_messages
 from langgraph.types import Command  # noqa: TC002
 from langgraph.typing import ContextT
-from typing_extensions import NotRequired, Required, TypedDict, TypeVar
+from typing_extensions import NotRequired, Required, TypedDict, TypeVar, Unpack
 
 if TYPE_CHECKING:
     from langchain_core.language_models.chat_models import BaseChatModel
@@ -62,6 +62,18 @@ JumpTo = Literal["tools", "model", "end"]
 ResponseT = TypeVar("ResponseT")
 
 
+class _ModelRequestOverrides(TypedDict, total=False):
+    """Possible overrides for ModelRequest.override() method."""
+
+    model: BaseChatModel
+    system_prompt: str | None
+    messages: list[AnyMessage]
+    tool_choice: Any | None
+    tools: list[BaseTool | dict]
+    response_format: ResponseFormat | None
+    model_settings: dict[str, Any]
+
+
 @dataclass
 class ModelRequest:
     """Model request information for the agent."""
@@ -76,6 +88,36 @@ class ModelRequest:
     runtime: Runtime[ContextT]  # type: ignore[valid-type]
     model_settings: dict[str, Any] = field(default_factory=dict)
 
+    def override(self, **overrides: Unpack[_ModelRequestOverrides]) -> ModelRequest:
+        """Replace the request with a new request with the given overrides.
+
+        Returns a new `ModelRequest` instance with the specified attributes replaced.
+        This follows an immutable pattern, leaving the original request unchanged.
+
+        Args:
+            **overrides: Keyword arguments for attributes to override. Supported keys:
+                - model: BaseChatModel instance
+                - system_prompt: Optional system prompt string
+                - messages: List of messages
+                - tool_choice: Tool choice configuration
+                - tools: List of available tools
+                - response_format: Response format specification
+                - model_settings: Additional model settings
+
+        Returns:
+            New ModelRequest instance with specified overrides applied.
+
+        Examples:
+            ```python
+            # Create a new request with different model
+            new_request = request.override(model=different_model)
+
+            # Override multiple attributes
+            new_request = request.override(system_prompt="New instructions", tool_choice="auto")
+            ```
+        """
+        return replace(self, **overrides)
+
 
 @dataclass
 class ModelResponse:

libs/langchain_v1/langchain/tools/tool_node.py

@@ -81,6 +81,7 @@ from langgraph.graph.message import REMOVE_ALL_MESSAGES
 from langgraph.runtime import get_runtime
 from langgraph.types import Command, Send
 from pydantic import BaseModel, ValidationError
+from typing_extensions import Unpack
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
@@ -104,6 +105,12 @@ TOOL_INVOCATION_ERROR_TEMPLATE = (
 )
 
 
+class _ToolCallRequestOverrides(TypedDict, total=False):
+    """Possible overrides for ToolCallRequest.override() method."""
+
+    tool_call: ToolCall
+
+
 @dataclass()
 class ToolCallRequest:
     """Tool execution request passed to tool call interceptors.
@@ -120,6 +127,31 @@ class ToolCallRequest:
     state: Any
     runtime: Any
 
+    def override(self, **overrides: Unpack[_ToolCallRequestOverrides]) -> ToolCallRequest:
+        """Replace the request with a new request with the given overrides.
+
+        Returns a new `ToolCallRequest` instance with the specified attributes replaced.
+        This follows an immutable pattern, leaving the original request unchanged.
+
+        Args:
+            **overrides: Keyword arguments for attributes to override. Supported keys:
+                - tool_call: Tool call dict with name, args, and id
+
+        Returns:
+            New ToolCallRequest instance with specified overrides applied.
+
+        Examples:
+            ```python
+            # Modify tool call arguments without mutating original
+            modified_call = {**request.tool_call, "args": {"value": 10}}
+            new_request = request.override(tool_call=modified_call)
+
+            # Override multiple attributes
+            new_request = request.override(tool_call=modified_call, state=new_state)
+            ```
+        """
+        return replace(self, **overrides)
+
 
 ToolCallWrapper = Callable[
     [ToolCallRequest, Callable[[ToolCallRequest], ToolMessage | Command]],

libs/langchain_v1/tests/unit_tests/agents/middleware/test_override_methods.py

@@ -0,0 +1,381 @@
+"""Unit tests for override() methods on ModelRequest and ToolCallRequest."""
+
+import pytest
+from langchain_core.language_models.fake_chat_models import GenericFakeChatModel
+from langchain_core.messages import AIMessage, HumanMessage
+from langchain_core.tools import BaseTool
+
+from langchain.agents.middleware.types import ModelRequest
+from langchain.tools.tool_node import ToolCallRequest
+
+
+class TestModelRequestOverride:
+    """Test the ModelRequest.override() method."""
+
+    def test_override_single_attribute(self) -> None:
+        """Test overriding a single attribute."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_request = ModelRequest(
+            model=model,
+            system_prompt="Original prompt",
+            messages=[HumanMessage("Hi")],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        new_request = original_request.override(system_prompt="New prompt")
+
+        # New request should have the overridden value
+        assert new_request.system_prompt == "New prompt"
+        # Original request should be unchanged (immutability)
+        assert original_request.system_prompt == "Original prompt"
+        # Other attributes should be the same
+        assert new_request.model == original_request.model
+        assert new_request.messages == original_request.messages
+
+    def test_override_multiple_attributes(self) -> None:
+        """Test overriding multiple attributes at once."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_request = ModelRequest(
+            model=model,
+            system_prompt="Original prompt",
+            messages=[HumanMessage("Hi")],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={"count": 1},
+            runtime=None,
+        )
+
+        new_request = original_request.override(
+            system_prompt="New prompt",
+            tool_choice="auto",
+            state={"count": 2},
+        )
+
+        # Overridden values should be changed
+        assert new_request.system_prompt == "New prompt"
+        assert new_request.tool_choice == "auto"
+        assert new_request.state == {"count": 2}
+        # Original should be unchanged
+        assert original_request.system_prompt == "Original prompt"
+        assert original_request.tool_choice is None
+        assert original_request.state == {"count": 1}
+
+    def test_override_messages(self) -> None:
+        """Test overriding messages list."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_messages = [HumanMessage("Hi")]
+        new_messages = [HumanMessage("Hello"), AIMessage("Hi there")]
+
+        original_request = ModelRequest(
+            model=model,
+            system_prompt=None,
+            messages=original_messages,
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        new_request = original_request.override(messages=new_messages)
+
+        assert new_request.messages == new_messages
+        assert original_request.messages == original_messages
+        assert len(new_request.messages) == 2
+        assert len(original_request.messages) == 1
+
+    def test_override_model_settings(self) -> None:
+        """Test overriding model_settings dict."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_request = ModelRequest(
+            model=model,
+            system_prompt=None,
+            messages=[HumanMessage("Hi")],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+            model_settings={"temperature": 0.5},
+        )
+
+        new_request = original_request.override(
+            model_settings={"temperature": 0.9, "max_tokens": 100}
+        )
+
+        assert new_request.model_settings == {"temperature": 0.9, "max_tokens": 100}
+        assert original_request.model_settings == {"temperature": 0.5}
+
+    def test_override_with_none_value(self) -> None:
+        """Test overriding with None value."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_request = ModelRequest(
+            model=model,
+            system_prompt="Original prompt",
+            messages=[HumanMessage("Hi")],
+            tool_choice="auto",
+            tools=[],
+            response_format=None,
+            state={},
+            runtime=None,
+        )
+
+        new_request = original_request.override(
+            system_prompt=None,
+            tool_choice=None,
+        )
+
+        assert new_request.system_prompt is None
+        assert new_request.tool_choice is None
+        assert original_request.system_prompt == "Original prompt"
+        assert original_request.tool_choice == "auto"
+
+    def test_override_preserves_identity_of_unchanged_objects(self) -> None:
+        """Test that unchanged attributes maintain object identity."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        messages = [HumanMessage("Hi")]
+        state = {"key": "value"}
+
+        original_request = ModelRequest(
+            model=model,
+            system_prompt="Original prompt",
+            messages=messages,
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state=state,
+            runtime=None,
+        )
+
+        new_request = original_request.override(system_prompt="New prompt")
+
+        # Unchanged objects should be the same instance
+        assert new_request.messages is messages
+        assert new_request.state is state
+        assert new_request.model is model
+
+    def test_override_chaining(self) -> None:
+        """Test chaining multiple override calls."""
+        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
+        original_request = ModelRequest(
+            model=model,
+            system_prompt="Prompt 1",
+            messages=[HumanMessage("Hi")],
+            tool_choice=None,
+            tools=[],
+            response_format=None,
+            state={"count": 1},
+            runtime=None,
+        )
+
+        final_request = (
+            original_request.override(system_prompt="Prompt 2")
+            .override(state={"count": 2})
+            .override(tool_choice="auto")
+        )
+
+        assert final_request.system_prompt == "Prompt 2"
+        assert final_request.state == {"count": 2}
+        assert final_request.tool_choice == "auto"
+        # Original should be unchanged
+        assert original_request.system_prompt == "Prompt 1"
+        assert original_request.state == {"count": 1}
+        assert original_request.tool_choice is None
+
+
+class TestToolCallRequestOverride:
+    """Test the ToolCallRequest.override() method."""
+
+    def test_override_tool_call(self) -> None:
+        """Test overriding tool_call dict."""
+        from langchain_core.tools import tool
+
+        @tool
+        def test_tool(x: int) -> str:
+            """A test tool."""
+            return f"Result: {x}"
+
+        original_call = {"name": "test_tool", "args": {"x": 5}, "id": "1", "type": "tool_call"}
+        modified_call = {"name": "test_tool", "args": {"x": 10}, "id": "1", "type": "tool_call"}
+
+        original_request = ToolCallRequest(
+            tool_call=original_call,
+            tool=test_tool,
+            state={"messages": []},
+            runtime=None,
+        )
+
+        new_request = original_request.override(tool_call=modified_call)
+
+        # New request should have modified tool_call
+        assert new_request.tool_call["args"]["x"] == 10
+        # Original should be unchanged
+        assert original_request.tool_call["args"]["x"] == 5
+        # Other attributes should be the same
+        assert new_request.tool is original_request.tool
+        assert new_request.state is original_request.state
+
+    def test_override_state(self) -> None:
+        """Test overriding state."""
+        from langchain_core.tools import tool
+
+        @tool
+        def test_tool(x: int) -> str:
+            """A test tool."""
+            return f"Result: {x}"
+
+        tool_call = {"name": "test_tool", "args": {"x": 5}, "id": "1", "type": "tool_call"}
+        original_state = {"messages": [HumanMessage("Hi")]}
+        new_state = {"messages": [HumanMessage("Hi"), AIMessage("Hello")]}
+
+        original_request = ToolCallRequest(
+            tool_call=tool_call,
+            tool=test_tool,
+            state=original_state,
+            runtime=None,
+        )
+
+        new_request = original_request.override(state=new_state)
+
+        assert len(new_request.state["messages"]) == 2
+        assert len(original_request.state["messages"]) == 1
+
+    def test_override_multiple_attributes(self) -> None:
+        """Test overriding multiple attributes at once."""
+        from langchain_core.tools import tool
+
+        @tool
+        def test_tool(x: int) -> str:
+            """A test tool."""
+            return f"Result: {x}"
+
+        @tool
+        def another_tool(y: str) -> str:
+            """Another test tool."""
+            return f"Output: {y}"
+
+        original_call = {"name": "test_tool", "args": {"x": 5}, "id": "1", "type": "tool_call"}
+        modified_call = {
+            "name": "another_tool",
+            "args": {"y": "hello"},
+            "id": "2",
+            "type": "tool_call",
+        }
+
+        original_request = ToolCallRequest(
+            tool_call=original_call,
+            tool=test_tool,
+            state={"count": 1},
+            runtime=None,
+        )
+
+        new_request = original_request.override(
+            tool_call=modified_call,
+            tool=another_tool,
+            state={"count": 2},
+        )
+
+        assert new_request.tool_call["name"] == "another_tool"
+        assert new_request.tool.name == "another_tool"
+        assert new_request.state == {"count": 2}
+        # Original unchanged
+        assert original_request.tool_call["name"] == "test_tool"
+        assert original_request.tool.name == "test_tool"
+        assert original_request.state == {"count": 1}
+
+    def test_override_with_copy_pattern(self) -> None:
+        """Test common pattern of copying and modifying tool_call."""
+        from langchain_core.tools import tool
+
+        @tool
+        def test_tool(value: int) -> str:
+            """A test tool."""
+            return f"Result: {value}"
+
+        original_call = {
+            "name": "test_tool",
+            "args": {"value": 5},
+            "id": "call_123",
+            "type": "tool_call",
+        }
+
+        original_request = ToolCallRequest(
+            tool_call=original_call,
+            tool=test_tool,
+            state={},
+            runtime=None,
+        )
+
+        # Common pattern: copy tool_call and modify args
+        modified_call = {**original_request.tool_call, "args": {"value": 10}}
+        new_request = original_request.override(tool_call=modified_call)
+
+        assert new_request.tool_call["args"]["value"] == 10
+        assert new_request.tool_call["id"] == "call_123"
+        assert new_request.tool_call["name"] == "test_tool"
+        # Original unchanged
+        assert original_request.tool_call["args"]["value"] == 5
+
+    def test_override_preserves_identity(self) -> None:
+        """Test that unchanged attributes maintain object identity."""
+        from langchain_core.tools import tool
+
+        @tool
+        def test_tool(x: int) -> str:
+            """A test tool."""
+            return f"Result: {x}"
+
+        tool_call = {"name": "test_tool", "args": {"x": 5}, "id": "1", "type": "tool_call"}
+        state = {"messages": []}
+
+        original_request = ToolCallRequest(
+            tool_call=tool_call,
+            tool=test_tool,
+            state=state,
+            runtime=None,
+        )
+
+        new_call = {"name": "test_tool", "args": {"x": 10}, "id": "1", "type": "tool_call"}
+        new_request = original_request.override(tool_call=new_call)
+
+        # Unchanged objects should be the same instance
+        assert new_request.tool is test_tool
+        assert new_request.state is state
+
+    def test_override_chaining(self) -> None:
+        """Test chaining multiple override calls."""
+        from langchain_core.tools import tool
+
+        @tool
+        def test_tool(x: int) -> str:
+            """A test tool."""
+            return f"Result: {x}"
+
+        tool_call = {"name": "test_tool", "args": {"x": 5}, "id": "1", "type": "tool_call"}
+
+        original_request = ToolCallRequest(
+            tool_call=tool_call,
+            tool=test_tool,
+            state={"count": 1},
+            runtime=None,
+        )
+
+        call_2 = {"name": "test_tool", "args": {"x": 10}, "id": "1", "type": "tool_call"}
+        call_3 = {"name": "test_tool", "args": {"x": 15}, "id": "1", "type": "tool_call"}
+
+        final_request = (
+            original_request.override(tool_call=call_2)
+            .override(state={"count": 2})
+            .override(tool_call=call_3)
+        )
+
+        assert final_request.tool_call["args"]["x"] == 15
+        assert final_request.state == {"count": 2}
+        # Original unchanged
+        assert original_request.tool_call["args"]["x"] == 5
+        assert original_request.state == {"count": 1}