RunnableConfigurableFields doesn't exclude excluded fields of the underlying class

Checked other resources

[X] I added a very descriptive title to this issue.
[X] I searched the LangChain documentation with the integrated search.
[X] I used the GitHub search to find a similar question and didn't find it.
[X] I am sure that this is a bug in LangChain rather than my code.
[X] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

from langchain.schema.runnable import ConfigurableField, RunnableSerializable
from pydantic import Field, model_validator

class Greeting(RunnableSerializable[str, str]):
    greeting: str = "Hello"
    private_greeting: str = Field(default=None, exclude=True)

    @model_validator(mode="after")
    def post_init(self):
        if self.private_greeting is None:
            self.private_greeting = self.greeting.upper()
        return self

    def invoke(self, input: str, config=None, **kwargs) -> str:
        return self.private_greeting + ", " + input.capitalize() + "!"

r = Greeting().configurable_fields(
    greeting=ConfigurableField(id="greeting"),
)

# Actual  : HELLO, World!
# Expected: GOODBYE, World!
print(r.invoke("world", config={"configurable": {"greeting": "Goodbye"}}))

Error Message and Stack Trace (if applicable)

No response

Description

The Langchain Serializable is based on BaseModel from Pydantic.

A typical way to define a certain field as private in BaseModel is:

to define it as Field(default=None, exclude=True) (meaning that (a) it's optional in the constructor and (b) its value isn't required to re-create the object from its serialized representation)
initialize the fields in a model_validator.

Such private fields are usually derived from the model public fields.

This is for example how langchain_openai defines client and async_client fields:

https://github.com/langchain-ai/langchain/blob/9404e7af9d8768a7e884dae3e9fafb712eaf4e99/libs/partners/openai/langchain_openai/chat_models/base.py#L378-L381

Now, configurable_fields method creates RunnableConfigurableFields object, which upon invoking recreates the underlying Runnable with the fields provided in configurable.

https://github.com/langchain-ai/langchain/blob/9404e7af9d8768a7e884dae3e9fafb712eaf4e99/libs/core/langchain_core/runnables/configurable.py#L440-L448

Note, that every single model field is passed to the class constructor including Excluded fields.

Consider a BaseModel with a public field A and an excluded field B populated by A (potentially by a complex logic).

The user has only the knowledge of A since it's a part of the public interface. So one tries to configure field A. But given that RunnableConfigurableFields passes both A and B to a new instance, the change of A won't affect B. See the minimal example attached.

This also precludes a user from a straightforward configuring of langchain_openai.ChatOpenAI via api_key: https://github.com/langchain-ai/langserve/issues/652 Since the excluded client-fields are derived from api_key, one has to resort to a cumbersome configuration of these client-fields too.

The proposed solution is to filter out the excluded fields when a new object is created:

if configurable:
    init_params = {
        k: v
        for k, v in self.default.__dict__.items()
-        if k in self.default.model_fields 
+        if k in self.default.model_fields and not self.default.model_fields[k].exclude
    }
    return (
        self.default.__class__(**{**init_params, **configurable}),
        config,
    )

System Info

System Information

OS: Darwin OS Version: Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:30 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6000 Python Version: 3.11.10 (main, Sep 7 2024, 01:03:31) [Clang 15.0.0 (clang-1500.3.9.4)]

Package Information

langchain_core: 0.3.1 langchain: 0.3.0 langchain_community: 0.0.38 langsmith: 0.1.126 langchain_openai: 0.2.0 langchain_text_splitters: 0.3.0 langserve: Installed. No version info available.

Optional packages not installed

langgraph

Other Dependencies

aiohttp: 3.10.5 aiosqlite: Installed. No version info available. aleph-alpha-client: Installed. No version info available. anthropic: Installed. No version info available. arxiv: Installed. No version info available. assemblyai: Installed. No version info available. async-timeout: Installed. No version info available. atlassian-python-api: Installed. No version info available. azure-ai-documentintelligence: Installed. No version info available. azure-identity: Installed. No version info available. azure-search-documents: Installed. No version info available. beautifulsoup4: Installed. No version info available. bibtexparser: Installed. No version info available. cassio: Installed. No version info available. chardet: Installed. No version info available. cloudpickle: Installed. No version info available. cohere: Installed. No version info available. databricks-vectorsearch: Installed. No version info available. dataclasses-json: 0.6.7 datasets: Installed. No version info available. dgml-utils: Installed. No version info available. elasticsearch: Installed. No version info available. esprima: Installed. No version info available. faiss-cpu: Installed. No version info available. feedparser: Installed. No version info available. fireworks-ai: Installed. No version info available. friendli-client: Installed. No version info available. geopandas: Installed. No version info available. gitpython: Installed. No version info available. google-cloud-documentai: Installed. No version info available. gql: Installed. No version info available. gradientai: Installed. No version info available. hdbcli: Installed. No version info available. hologres-vector: Installed. No version info available. html2text: Installed. No version info available. httpx: 0.27.2 httpx-sse: Installed. No version info available. javelin-sdk: Installed. No version info available. jinja2: Installed. No version info available. jq: Installed. No version info available. jsonpatch: 1.33 jsonschema: Installed. No version info available. lxml: Installed. No version info available. markdownify: Installed. No version info available. motor: Installed. No version info available. msal: Installed. No version info available. mwparserfromhell: Installed. No version info available. mwxml: Installed. No version info available. newspaper3k: Installed. No version info available. numexpr: Installed. No version info available. numpy: 1.26.4 nvidia-riva-client: Installed. No version info available. oci: Installed. No version info available. openai: 1.46.0 openapi-pydantic: Installed. No version info available. oracle-ads: Installed. No version info available. oracledb: Installed. No version info available. orjson: 3.10.7 packaging: 23.2 pandas: Installed. No version info available. pdfminer-six: Installed. No version info available. pgvector: Installed. No version info available. praw: Installed. No version info available. premai: Installed. No version info available. psychicapi: Installed. No version info available. py-trello: Installed. No version info available. pydantic: 2.9.2 pyjwt: Installed. No version info available. pymupdf: Installed. No version info available. pypdf: Installed. No version info available. pypdfium2: Installed. No version info available. pyspark: Installed. No version info available. PyYAML: 6.0.2 rank-bm25: Installed. No version info available. rapidfuzz: Installed. No version info available. rapidocr-onnxruntime: Installed. No version info available. rdflib: Installed. No version info available. requests: 2.32.3 requests-toolbelt: Installed. No version info available. rspace_client: Installed. No version info available. scikit-learn: Installed. No version info available. SQLAlchemy: 2.0.35 sqlite-vss: Installed. No version info available. streamlit: Installed. No version info available. sympy: Installed. No version info available. telethon: Installed. No version info available. tenacity: 8.5.0 tidb-vector: Installed. No version info available. tiktoken: 0.7.0 timescale-vector: Installed. No version info available. tqdm: 4.66.5 tree-sitter: Installed. No version info available. tree-sitter-languages: Installed. No version info available. typer: Installed. No version info available. typing-extensions: 4.12.2 upstash-redis: Installed. No version info available. vdms: Installed. No version info available. xata: Installed. No version info available. xmltodict: Installed. No version info available.

langchain-ai / langchain