Feature: jsonable_encoder should pass context to pydantic models

fastapi/_compat.py

@@ -447,6 +447,8 @@ else:
     def _model_dump(
         model: BaseModel, mode: Literal["json", "python"] = "json", **kwargs: Any
     ) -> Any:
+        if not PYDANTIC_V2:
+            kwargs.pop("context", None)
         return model.dict(**kwargs)
 
     def _get_model_config(model: BaseModel) -> Any:

fastapi/encoders.py

@@ -126,6 +126,14 @@ def jsonable_encoder(
             """
         ),
     ] = None,
+    context: Annotated[
+        Optional[Any],
+        Doc(
+            """
+            Pydantic's `context` parameter, passed to Pydantic serializers.
+            """
+        ),
+    ] = None,
     by_alias: Annotated[
         bool,
         Doc(
@@ -225,6 +233,7 @@ def jsonable_encoder(
             mode="json",
             include=include,
             exclude=exclude,
+            context=context,
             by_alias=by_alias,
             exclude_unset=exclude_unset,
             exclude_none=exclude_none,
@@ -234,6 +243,7 @@ def jsonable_encoder(
             obj_dict = obj_dict["__root__"]
         return jsonable_encoder(
             obj_dict,
+            context=context,
             exclude_none=exclude_none,
             exclude_defaults=exclude_defaults,
             # TODO: remove when deprecating Pydantic v1
@@ -246,6 +256,7 @@ def jsonable_encoder(
             obj_dict,
             include=include,
             exclude=exclude,
+            context=context,
             by_alias=by_alias,
             exclude_unset=exclude_unset,
             exclude_defaults=exclude_defaults,
@@ -280,6 +291,7 @@ def jsonable_encoder(
             ):
                 encoded_key = jsonable_encoder(
                     key,
+                    context=context,
                     by_alias=by_alias,
                     exclude_unset=exclude_unset,
                     exclude_none=exclude_none,
@@ -288,6 +300,7 @@ def jsonable_encoder(
                 )
                 encoded_value = jsonable_encoder(
                     value,
+                    context=context,
                     by_alias=by_alias,
                     exclude_unset=exclude_unset,
                     exclude_none=exclude_none,
@@ -304,6 +317,7 @@ def jsonable_encoder(
                     item,
                     include=include,
                     exclude=exclude,
+                    context=context,
                     by_alias=by_alias,
                     exclude_unset=exclude_unset,
                     exclude_defaults=exclude_defaults,
@@ -334,6 +348,7 @@ def jsonable_encoder(
         data,
         include=include,
         exclude=exclude,
+        context=context,
         by_alias=by_alias,
         exclude_unset=exclude_unset,
         exclude_defaults=exclude_defaults,

tests/test_compat.py

@@ -5,6 +5,7 @@ from fastapi._compat import (
     ModelField,
     Undefined,
     _get_model_config,
+    _model_dump,
     get_cached_model_fields,
     get_model_fields,
     is_bytes_sequence_annotation,
@@ -118,3 +119,13 @@ def test_get_model_fields_cached():
 
     assert non_cached_fields is not non_cached_fields2
     assert cached_fields is cached_fields2
+
+
+@needs_pydanticv1
+def test_model_dump_remove_context_kwarg_in_pydanticv1() -> None:
+    class Model(BaseModel):
+        foo: str
+
+    # The following instruction would throw an error
+    # in pv1 if the context kwarg was not removed.
+    _model_dump(Model(foo="bar"), context=1)

tests/test_jsonable_encoder.py

@@ -9,7 +9,11 @@ from typing import Optional
 import pytest
 from fastapi._compat import PYDANTIC_V2, Undefined
 from fastapi.encoders import jsonable_encoder
-from pydantic import BaseModel, Field, ValidationError
+from pydantic import (
+    BaseModel,
+    Field,
+    ValidationError,
+)
 
 from .utils import needs_pydanticv1, needs_pydanticv2
 
@@ -316,3 +320,25 @@ def test_encode_deque_encodes_child_models():
 def test_encode_pydantic_undefined():
     data = {"value": Undefined}
     assert jsonable_encoder(data) == {"value": None}
+
+
+@needs_pydanticv2
+def test_encode_with_context() -> None:
+    from pydantic import SerializationInfo, field_serializer
+
+    class ModelWithContextualSerializer(BaseModel):
+        value: int
+
+        @field_serializer("value")
+        def serialize_value(value: int, info: SerializationInfo) -> int:
+            if info.context is not None and isinstance(
+                value_from_context := info.context.get("value"), int
+            ):
+                return value_from_context
+
+            return value
+
+    model = ModelWithContextualSerializer(value=1)
+
+    assert jsonable_encoder(model) == {"value": 1}
+    assert jsonable_encoder(model, context={"value": 2}) == {"value": 2}