Using pydantic custom encoders (#21)

Add support for Pydantic custom JSON encoders.

fastapi/encoders.py

@@ -12,12 +12,20 @@ def jsonable_encoder(
     exclude: Set[str] = set(),
     by_alias: bool = False,
     include_none: bool = True,
+    custom_encoder: dict = {},
 ) -> Any:
     if isinstance(obj, BaseModel):
-        return jsonable_encoder(
-            obj.dict(include=include, exclude=exclude, by_alias=by_alias),
-            include_none=include_none,
-        )
+        if not obj.Config.json_encoders:
+            return jsonable_encoder(
+                obj.dict(include=include, exclude=exclude, by_alias=by_alias),
+                include_none=include_none,
+            )
+        else:
+            return jsonable_encoder(
+                obj.dict(include=include, exclude=exclude, by_alias=by_alias),
+                include_none=include_none,
+                custom_encoder=obj.Config.json_encoders,
+            )
     if isinstance(obj, Enum):
         return obj.value
     if isinstance(obj, (str, int, float, type(None))):
@@ -25,8 +33,16 @@ def jsonable_encoder(
     if isinstance(obj, dict):
         return {
             jsonable_encoder(
-                key, by_alias=by_alias, include_none=include_none
-            ): jsonable_encoder(value, by_alias=by_alias, include_none=include_none)
+                key,
+                by_alias=by_alias,
+                include_none=include_none,
+                custom_encoder=custom_encoder,
+            ): jsonable_encoder(
+                value,
+                by_alias=by_alias,
+                include_none=include_none,
+                custom_encoder=custom_encoder,
+            )
             for key, value in obj.items()
             if value is not None or include_none
         }
@@ -38,12 +54,16 @@ def jsonable_encoder(
                 exclude=exclude,
                 by_alias=by_alias,
                 include_none=include_none,
+                custom_encoder=custom_encoder,
             )
             for item in obj
         ]
     errors = []
     try:
-        encoder = ENCODERS_BY_TYPE[type(obj)]
+        if custom_encoder and type(obj) in custom_encoder:
+            encoder = custom_encoder[type(obj)]
+        else:
+            encoder = ENCODERS_BY_TYPE[type(obj)]
         return encoder(obj)
     except KeyError as e:
         errors.append(e)

tests/test_datetime.py

@@ -0,0 +1,35 @@
+import json
+from datetime import datetime, timezone
+
+from fastapi import FastAPI
+from pydantic import BaseModel
+from starlette.testclient import TestClient
+
+
+class ModelWithDatetimeField(BaseModel):
+    dt_field: datetime
+
+    class Config:
+        json_encoders = {
+            datetime: lambda dt: dt.replace(
+                microsecond=0, tzinfo=timezone.utc
+            ).isoformat()
+        }
+
+
+app = FastAPI()
+model = ModelWithDatetimeField(dt_field=datetime.utcnow())
+
+
+@app.get("/model", response_model=ModelWithDatetimeField)
+def get_model():
+    return model
+
+
+client = TestClient(app)
+
+
+def test_dt():
+    with client:
+        response = client.get("/model")
+    assert json.loads(model.json()) == response.json()