add: option to generate api specification by field name instead of alias

docs/en/docs/how-to/extending-openapi.md

@@ -26,6 +26,7 @@ And that function `get_openapi()` receives as parameters:
 * `summary`: A short summary of the API.
 * `description`: The description of your API, this can include markdown and will be shown in the docs.
 * `routes`: A list of routes, these are each of the registered *path operations*. They are taken from `app.routes`.
+* `field_names_by_alias`: A boolean indicating whether to use the field names or the alias names for the models.
 
 !!! info
     The parameter `summary` is available in OpenAPI 3.1.0 and above, supported by FastAPI 0.99.0 and above.

fastapi/openapi/utils.py

@@ -450,6 +450,7 @@ def get_openapi(
     contact: Optional[Dict[str, Union[str, Any]]] = None,
     license_info: Optional[Dict[str, Union[str, Any]]] = None,
     separate_input_output_schemas: bool = True,
+    field_names_by_alias: bool = True,
 ) -> Dict[str, Any]:
     info: Dict[str, Any] = {"title": title, "version": version}
     if summary:
@@ -471,7 +472,9 @@ def get_openapi(
     operation_ids: Set[str] = set()
     all_fields = get_fields_from_routes(list(routes or []) + list(webhooks or []))
     model_name_map = get_compat_model_name_map(all_fields)
-    schema_generator = GenerateJsonSchema(ref_template=REF_TEMPLATE)
+    schema_generator = GenerateJsonSchema(
+        ref_template=REF_TEMPLATE, by_alias=field_names_by_alias
+    )
     field_mapping, definitions = get_definitions(
         fields=all_fields,
         schema_generator=schema_generator,