core[minor]: Add support for pydantic 2 to utility to get fields (#24899)

Add compatibility for pydantic 2 for a utility function.

This will help push some small changes to master, so they don't have to
be kept track of on a separate branch.

libs/core/langchain_core/utils/pydantic.py

@@ -41,6 +41,18 @@ else:
 TBaseModel = TypeVar("TBaseModel", bound=PydanticBaseModel)
 
 
+def is_pydantic_v1_subclass(cls: Type) -> bool:
+    """Check if the installed Pydantic version is 1.x-like."""
+    if PYDANTIC_MAJOR_VERSION == 1:
+        return True
+    elif PYDANTIC_MAJOR_VERSION == 2:
+        from pydantic.v1 import BaseModel as BaseModelV1
+
+        if issubclass(cls, BaseModelV1):
+            return True
+    return False
+
+
 def is_basemodel_subclass(cls: Type) -> bool:
     """Check if the given class is a subclass of Pydantic BaseModel.
 

libs/core/langchain_core/utils/utils.py

@@ -12,6 +12,9 @@ from packaging.version import parse
 from requests import HTTPError, Response
 
 from langchain_core.pydantic_v1 import SecretStr
+from langchain_core.utils.pydantic import (
+    is_pydantic_v1_subclass,
+)
 
 
 def xor_args(*arg_groups: Tuple[str, ...]) -> Callable:
@@ -192,10 +195,16 @@ def get_pydantic_field_names(pydantic_cls: Any) -> Set[str]:
         Set[str]: Field names.
     """
     all_required_field_names = set()
-    for field in pydantic_cls.__fields__.values():
+    if is_pydantic_v1_subclass(pydantic_cls):
-        all_required_field_names.add(field.name)
+        for field in pydantic_cls.__fields__.values():
-        if field.has_alias:
+            all_required_field_names.add(field.name)
-            all_required_field_names.add(field.alias)
+            if field.has_alias:
+                all_required_field_names.add(field.alias)
+    else:  # Assuming pydantic 2 for now
+        for name, field in pydantic_cls.model_fields.items():
+            all_required_field_names.add(name)
+            if field.alias:
+                all_required_field_names.add(field.alias)
     return all_required_field_names
 
 

libs/core/tests/unit_tests/utils/test_utils.py

@@ -6,8 +6,13 @@ from unittest.mock import patch
 import pytest
 
 from langchain_core import utils
-from langchain_core.utils import check_package_version, guard_import
+from langchain_core.utils import (
+    check_package_version,
+    get_pydantic_field_names,
+    guard_import,
+)
 from langchain_core.utils._merge import merge_dicts
+from langchain_core.utils.pydantic import PYDANTIC_MAJOR_VERSION
 
 
 @pytest.mark.parametrize(
@@ -171,3 +176,46 @@ def test_guard_import_failure(
         f"Please install it with `pip install {pip_name}`."
     )
     assert exc_info.value.msg == err_msg
+
+
+@pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 2, reason="Requires pydantic 2")
+def test_get_pydantic_field_names_v1_in_2() -> None:
+    from pydantic.v1 import BaseModel as PydanticV1BaseModel  # pydantic: ignore
+    from pydantic.v1 import Field  # pydantic: ignore
+
+    class PydanticV1Model(PydanticV1BaseModel):
+        field1: str
+        field2: int
+        alias_field: int = Field(alias="aliased_field")
+
+    result = get_pydantic_field_names(PydanticV1Model)
+    expected = {"field1", "field2", "aliased_field", "alias_field"}
+    assert result == expected
+
+
+@pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 2, reason="Requires pydantic 2")
+def test_get_pydantic_field_names_v2_in_2() -> None:
+    from pydantic import BaseModel, Field  # pydantic: ignore
+
+    class PydanticModel(BaseModel):
+        field1: str
+        field2: int
+        alias_field: int = Field(alias="aliased_field")
+
+    result = get_pydantic_field_names(PydanticModel)
+    expected = {"field1", "field2", "aliased_field", "alias_field"}
+    assert result == expected
+
+
+@pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 1, reason="Requires pydantic 1")
+def test_get_pydantic_field_names_v1() -> None:
+    from pydantic import BaseModel, Field  # pydantic: ignore
+
+    class PydanticModel(BaseModel):
+        field1: str
+        field2: int
+        alias_field: int = Field(alias="aliased_field")
+
+    result = get_pydantic_field_names(PydanticModel)
+    expected = {"field1", "field2", "aliased_field", "alias_field"}
+    assert result == expected