Add `validation_alias` and `serialization_alias` properties to `ModelField`

fastapi/_compat/v2.py

@@ -70,6 +70,18 @@ class ModelField:
         a = self.field_info.alias
         return a if a is not None else self.name
 
+    @property
+    def validation_alias(self) -> Union[str, None]:
+        va = self.field_info.validation_alias
+        if isinstance(va, str) and va:
+            return va
+        return None
+
+    @property
+    def serialization_alias(self) -> Union[str, None]:
+        sa = self.field_info.serialization_alias
+        return sa or None
+
     @property
     def required(self) -> bool:
         return self.field_info.is_required()
@@ -183,12 +195,18 @@ def get_schema_from_model_field(
     override_mode: Union[Literal["validation"], None] = (
         None if separate_input_output_schemas else "validation"
     )
+    field_alias = (
+        (field.validation_alias or field.alias)
+        if field.mode == "validation"
+        else (field.serialization_alias or field.alias)
+    )
+
     # This expects that GenerateJsonSchema was already used to generate the definitions
     json_schema = field_mapping[(field, override_mode or field.mode)]
     if "$ref" not in json_schema:
         # TODO remove when deprecating Pydantic v1
         # Ref: https://github.com/pydantic/pydantic/blob/d61792cc42c80b13b23e3ffa74bc37ec7c77f7d1/pydantic/schema.py#L207
-        json_schema["title"] = field.field_info.title or field.alias.title().replace(
+        json_schema["title"] = field.field_info.title or field_alias.title().replace(
             "_", " "
         )
     return json_schema

fastapi/dependencies/utils.py

@@ -722,7 +722,7 @@ def _validate_value_with_model_field(
 def _get_multidict_value(
     field: ModelField, values: Mapping[str, Any], alias: Union[str, None] = None
 ) -> Any:
-    alias = alias or field.alias
+    alias = alias or get_validation_alias(field)
     if is_sequence_field(field) and isinstance(values, (ImmutableMultiDict, Headers)):
         value = values.getlist(alias)
     else:
@@ -779,15 +779,13 @@ def request_params_to_args(
                 field.field_info, "convert_underscores", default_convert_underscores
             )
             if convert_underscores:
-                alias = (
+                alias = get_validation_alias(field)
-                    field.alias
+                if alias == field.name:
-                    if field.alias != field.name
+                    alias = alias.replace("_", "-")
-                    else field.name.replace("_", "-")
-                )
         value = _get_multidict_value(field, received_params, alias=alias)
         if value is not None:
             params_to_process[field.name] = value
-        processed_keys.add(alias or field.alias)
+        processed_keys.add(alias or get_validation_alias(field))
         processed_keys.add(field.name)
 
     for key, value in received_params.items():
@@ -811,7 +809,7 @@ def request_params_to_args(
         assert isinstance(field_info, (params.Param, temp_pydantic_v1_params.Param)), (
             "Params must be subclasses of Param"
         )
-        loc = (field_info.in_.value, field.alias)
+        loc = (field_info.in_.value, get_validation_alias(field))
         v_, errors_ = _validate_value_with_model_field(
             field=field, value=value, values=values, loc=loc
         )
@@ -900,7 +898,7 @@ async def _extract_form_body(
                     tg.start_soon(process_fn, sub_value.read)
             value = serialize_sequence_value(field=field, value=results)
         if value is not None:
-            values[field.alias] = value
+            values[get_validation_alias(field)] = value
     for key, value in received_body.items():
         if key not in values:
             values[key] = value
@@ -938,11 +936,11 @@ async def request_body_to_args(
         )
         return {first_field.name: v_}, errors_
     for field in body_fields:
-        loc = ("body", field.alias)
+        loc = ("body", get_validation_alias(field))
         value: Optional[Any] = None
         if body_to_process is not None:
             try:
-                value = body_to_process.get(field.alias)
+                value = body_to_process.get(get_validation_alias(field))
             # If the received body is a list, not a dict
             except AttributeError:
                 errors.append(get_missing_field_error(loc))
@@ -1021,3 +1019,8 @@ def get_body_field(
         field_info=BodyFieldInfo(**BodyFieldInfo_kwargs),
     )
     return final_field
+
+
+def get_validation_alias(field: ModelField) -> str:
+    va = getattr(field, "validation_alias", None)
+    return va or field.alias

fastapi/openapi/utils.py

@@ -19,6 +19,7 @@ from fastapi.dependencies.utils import (
     _get_flat_fields_from_params,
     get_flat_dependant,
     get_flat_params,
+    get_validation_alias,
 )
 from fastapi.encoders import jsonable_encoder
 from fastapi.openapi.constants import METHODS_WITH_BODY, REF_PREFIX
@@ -132,7 +133,7 @@ def _get_openapi_operation_parameters(
                 field_mapping=field_mapping,
                 separate_input_output_schemas=separate_input_output_schemas,
             )
-            name = param.alias
+            name = get_validation_alias(param)
             convert_underscores = getattr(
                 param.field_info,
                 "convert_underscores",
@@ -140,7 +141,7 @@ def _get_openapi_operation_parameters(
             )
             if (
                 param_type == ParamTypes.header
-                and param.alias == param.name
+                and name == param.name
                 and convert_underscores
             ):
                 name = param.name.replace("_", "-")