Implement OneOf Input Objects via @OneOf directive

Replicates graphql/graphql-js@8cfa3de

Author: Cito

src/graphql/__init__.py

@@ -259,6 +259,7 @@
     GraphQLStreamDirective,
     GraphQLDeprecatedDirective,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
     # "Enum" of Type Kinds
     TypeKind,
     # Constant Deprecation Reason
@@ -504,6 +505,7 @@
     "GraphQLStreamDirective",
     "GraphQLDeprecatedDirective",
     "GraphQLSpecifiedByDirective",
+    "GraphQLOneOfDirective",
     "TypeKind",
     "DEFAULT_DEPRECATION_REASON",
     "introspection_types",

src/graphql/execution/values.py

@@ -128,16 +128,20 @@ def coerce_variable_values(
             continue
 
         def on_input_value_error(
-            path: list[str | int], invalid_value: Any, error: GraphQLError
+            path: list[str | int],
+            invalid_value: Any,
+            error: GraphQLError,
+            var_name: str = var_name,
+            var_def_node: VariableDefinitionNode = var_def_node,
         ) -> None:
             invalid_str = inspect(invalid_value)
-            prefix = f"Variable '${var_name}' got invalid value {invalid_str}"  # noqa: B023
+            prefix = f"Variable '${var_name}' got invalid value {invalid_str}"
             if path:
-                prefix += f" at '{var_name}{print_path_list(path)}'"  # noqa: B023
+                prefix += f" at '{var_name}{print_path_list(path)}'"
             on_error(
                 GraphQLError(
                     prefix + "; " + error.message,
-                    var_def_node,  # noqa: B023
+                    var_def_node,
                     original_error=error,
                 )
             )
@@ -193,7 +197,8 @@ def get_argument_values(
                     )
                     raise GraphQLError(msg, value_node)
                 continue  # pragma: no cover
-            is_null = variable_values[variable_name] is None
+            variable_value = variable_values[variable_name]
+            is_null = variable_value is None or variable_value is Undefined
 
         if is_null and is_non_null_type(arg_type):
             msg = f"Argument '{name}' of non-null type '{arg_type}' must not be null."

src/graphql/type/__init__.py

@@ -137,6 +137,7 @@
     GraphQLStreamDirective,
     GraphQLDeprecatedDirective,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
     # Keyword Args
     GraphQLDirectiveKwargs,
     # Constant Deprecation Reason
@@ -286,6 +287,7 @@
     "GraphQLStreamDirective",
     "GraphQLDeprecatedDirective",
     "GraphQLSpecifiedByDirective",
+    "GraphQLOneOfDirective",
     "GraphQLDirectiveKwargs",
     "DEFAULT_DEPRECATION_REASON",
     "is_specified_scalar_type",

src/graphql/type/definition.py

@@ -1272,6 +1272,7 @@ class GraphQLInputObjectTypeKwargs(GraphQLNamedTypeKwargs, total=False):
 
     fields: GraphQLInputFieldMap
     out_type: GraphQLInputFieldOutType | None
+    is_one_of: bool
 
 
 class GraphQLInputObjectType(GraphQLNamedType):
@@ -1301,6 +1302,7 @@ class GeoPoint(GraphQLInputObjectType):
 
     ast_node: InputObjectTypeDefinitionNode | None
     extension_ast_nodes: tuple[InputObjectTypeExtensionNode, ...]
+    is_one_of: bool
 
     def __init__(
         self,
@@ -1311,6 +1313,7 @@ def __init__(
         extensions: dict[str, Any] | None = None,
         ast_node: InputObjectTypeDefinitionNode | None = None,
         extension_ast_nodes: Collection[InputObjectTypeExtensionNode] | None = None,
+        is_one_of: bool = False,
     ) -> None:
         super().__init__(
             name=name,
@@ -1322,6 +1325,7 @@ def __init__(
         self._fields = fields
         if out_type is not None:
             self.out_type = out_type  # type: ignore
+        self.is_one_of = is_one_of
 
     @staticmethod
     def out_type(value: dict[str, Any]) -> Any:
@@ -1340,6 +1344,7 @@ def to_kwargs(self) -> GraphQLInputObjectTypeKwargs:
             out_type=None
             if self.out_type is GraphQLInputObjectType.out_type
             else self.out_type,
+            is_one_of=self.is_one_of,
         )
 
     def __copy__(self) -> GraphQLInputObjectType:  # pragma: no cover

src/graphql/type/directives.py

@@ -261,11 +261,20 @@ def assert_directive(directive: Any) -> GraphQLDirective:
     description="Exposes a URL that specifies the behaviour of this scalar.",
 )
 
+# Used to declare an Input Object as a OneOf Input Objects.
+GraphQLOneOfDirective = GraphQLDirective(
+    name="oneOf",
+    locations=[DirectiveLocation.INPUT_OBJECT],
+    args={},
+    description="Indicates an Input Object is a OneOf Input Object.",
+)
+
 specified_directives: tuple[GraphQLDirective, ...] = (
     GraphQLIncludeDirective,
     GraphQLSkipDirective,
     GraphQLDeprecatedDirective,
     GraphQLSpecifiedByDirective,
+    GraphQLOneOfDirective,
 )
 """A tuple with all directives from the GraphQL specification"""
 

src/graphql/type/introspection.py

@@ -305,6 +305,7 @@ def __new__(cls):
                 resolve=cls.input_fields,
             ),
             "ofType": GraphQLField(_Type, resolve=cls.of_type),
+            "isOneOf": GraphQLField(GraphQLBoolean, resolve=cls.is_one_of),
         }
 
     @staticmethod
@@ -396,6 +397,10 @@ def input_fields(type_, _info, includeDeprecated=False):
     def of_type(type_, _info):
         return getattr(type_, "of_type", None)
 
+    @staticmethod
+    def is_one_of(type_, _info):
+        return type_.is_one_of if is_input_object_type(type_) else None
+
 
 _Type: GraphQLObjectType = GraphQLObjectType(
     name="__Type",

src/graphql/type/validate.py

@@ -16,7 +16,7 @@
     SchemaDefinitionNode,
     SchemaExtensionNode,
 )
-from ..pyutils import and_list, inspect
+from ..pyutils import Undefined, and_list, inspect
 from ..utilities.type_comparators import is_equal_type, is_type_sub_type_of
 from .definition import (
     GraphQLEnumType,
@@ -482,6 +482,28 @@ def validate_input_fields(self, input_obj: GraphQLInputObjectType) -> None:
                     ],
                 )
 
+            if input_obj.is_one_of:
+                self.validate_one_of_input_object_field(input_obj, field_name, field)
+
+    def validate_one_of_input_object_field(
+        self,
+        type_: GraphQLInputObjectType,
+        field_name: str,
+        field: GraphQLInputField,
+    ) -> None:
+        if is_non_null_type(field.type):
+            self.report_error(
+                f"OneOf input field {type_.name}.{field_name} must be nullable.",
+                field.ast_node and field.ast_node.type,
+            )
+
+        if field.default_value is not Undefined:
+            self.report_error(
+                f"OneOf input field {type_.name}.{field_name}"
+                " cannot have a default value.",
+                field.ast_node,
+            )
+
 
 def get_operation_type_node(
     schema: GraphQLSchema, operation: OperationType

src/graphql/utilities/coerce_input_value.py

@@ -130,6 +130,30 @@ def coerce_input_value(
                         + did_you_mean(suggestions)
                     ),
                 )
+
+        if type_.is_one_of:
+            keys = list(coerced_dict)
+            if len(keys) != 1:
+                on_error(
+                    path.as_list() if path else [],
+                    input_value,
+                    GraphQLError(
+                        "Exactly one key must be specified"
+                        f" for OneOf type '{type_.name}'.",
+                    ),
+                )
+            else:
+                key = keys[0]
+                value = coerced_dict[key]
+                if value is None:
+                    on_error(
+                        (path.as_list() if path else []) + [key],
+                        value,
+                        GraphQLError(
+                            f"Field '{key}' must be non-null.",
+                        ),
+                    )
+
         return type_.out_type(coerced_dict)
 
     if is_leaf_type(type_):

src/graphql/utilities/extend_schema.py

@@ -65,6 +65,7 @@
     GraphQLNullableType,
     GraphQLObjectType,
     GraphQLObjectTypeKwargs,
+    GraphQLOneOfDirective,
     GraphQLOutputType,
     GraphQLScalarType,
     GraphQLSchema,
@@ -777,6 +778,7 @@ def build_input_object_type(
             fields=partial(self.build_input_field_map, all_nodes),
             ast_node=ast_node,
             extension_ast_nodes=extension_nodes,
+            is_one_of=is_one_of(ast_node),
         )
 
     def build_type(self, ast_node: TypeDefinitionNode) -> GraphQLNamedType:
@@ -822,3 +824,10 @@ def get_specified_by_url(
 
     specified_by_url = get_directive_values(GraphQLSpecifiedByDirective, node)
     return specified_by_url["url"] if specified_by_url else None
+
+
+def is_one_of(node: InputObjectTypeDefinitionNode) -> bool:
+    """Given an input object node, returns if the node should be OneOf."""
+    from ..execution import get_directive_values
+
+    return get_directive_values(GraphQLOneOfDirective, node) is not None

src/graphql/utilities/value_from_ast.py

@@ -118,6 +118,14 @@ def value_from_ast(
                 return Undefined
             coerced_obj[field.out_name or field_name] = field_value
 
+        if type_.is_one_of:
+            keys = list(coerced_obj)
+            if len(keys) != 1:
+                return Undefined
+
+            if coerced_obj[keys[0]] is None:
+                return Undefined
+
         return type_.out_type(coerced_obj)
 
     if is_leaf_type(type_):