feat: Enable use of Undefined in InputObjectTypes (#1506)

* Changed InputObjectType's default builder-from-dict argument to be `Undefined` instead of `None`, removing ambiguity of undefined optional inputs using dot notation access syntax.

* Move `set_default_input_object_type_to_undefined()` fixture into conftest.py for sharing it between multiple test files.

graphene/types/inputobjecttype.py

@@ -14,6 +14,31 @@ class InputObjectTypeOptions(BaseOptions):
     container = None  # type: InputObjectTypeContainer
 
 
+# Currently in Graphene, we get a `None` whenever we access an (optional) field that was not set in an InputObjectType
+# using the InputObjectType.<attribute> dot access syntax. This is ambiguous, because in this current (Graphene
+# historical) arrangement, we cannot distinguish between a field not being set and a field being set to None.
+# At the same time, we shouldn't break existing code that expects a `None` when accessing a field that was not set.
+_INPUT_OBJECT_TYPE_DEFAULT_VALUE = None
+
+# To mitigate this, we provide the function `set_input_object_type_default_value` to allow users to change the default
+# value returned in non-specified fields in InputObjectType to another meaningful sentinel value (e.g. Undefined)
+# if they want to. This way, we can keep code that expects a `None` working while we figure out a better solution (or
+# a well-documented breaking change) for this issue.
+
+
+def set_input_object_type_default_value(default_value):
+    """
+    Change the sentinel value returned by non-specified fields in an InputObjectType
+    Useful to differentiate between a field not being set and a field being set to None by using a sentinel value
+    (e.g. Undefined is a good sentinel value for this purpose)
+
+    This function should be called at the beginning of the app or in some other place where it is guaranteed to
+    be called before any InputObjectType is defined.
+    """
+    global _INPUT_OBJECT_TYPE_DEFAULT_VALUE
+    _INPUT_OBJECT_TYPE_DEFAULT_VALUE = default_value
+
+
 class InputObjectTypeContainer(dict, BaseType):  # type: ignore
     class Meta:
         abstract = True
@@ -21,7 +46,7 @@ class InputObjectTypeContainer(dict, BaseType):  # type: ignore
     def __init__(self, *args, **kwargs):
         dict.__init__(self, *args, **kwargs)
         for key in self._meta.fields:
-            setattr(self, key, self.get(key, None))
+            setattr(self, key, self.get(key, _INPUT_OBJECT_TYPE_DEFAULT_VALUE))
 
     def __init_subclass__(cls, *args, **kwargs):
         pass

graphene/types/tests/conftest.py

@@ -0,0 +1,12 @@
+import pytest
+from graphql import Undefined
+
+from graphene.types.inputobjecttype import set_input_object_type_default_value
+
+
+@pytest.fixture()
+def set_default_input_object_type_to_undefined():
+    """This fixture is used to change the default value of optional inputs in InputObjectTypes for specific tests"""
+    set_input_object_type_default_value(Undefined)
+    yield
+    set_input_object_type_default_value(None)

graphene/types/tests/test_inputobjecttype.py

@@ -1,3 +1,5 @@
+from graphql import Undefined
+
 from ..argument import Argument
 from ..field import Field
 from ..inputfield import InputField
@@ -6,6 +8,7 @@ from ..objecttype import ObjectType
 from ..scalars import Boolean, String
 from ..schema import Schema
 from ..unmountedtype import UnmountedType
+from ... import NonNull
 
 
 class MyType:
@@ -136,3 +139,31 @@ def test_inputobjecttype_of_input():
 
     assert not result.errors
     assert result.data == {"isChild": True}
+
+
+def test_inputobjecttype_default_input_as_undefined(
+    set_default_input_object_type_to_undefined,
+):
+    class TestUndefinedInput(InputObjectType):
+        required_field = String(required=True)
+        optional_field = String()
+
+    class Query(ObjectType):
+        undefined_optionals_work = Field(NonNull(Boolean), input=TestUndefinedInput())
+
+        def resolve_undefined_optionals_work(self, info, input: TestUndefinedInput):
+            # Confirm that optional_field comes as Undefined
+            return (
+                input.required_field == "required" and input.optional_field is Undefined
+            )
+
+    schema = Schema(query=Query)
+    result = schema.execute(
+        """query basequery {
+        undefinedOptionalsWork(input: {requiredField: "required"})
+    }
+    """
+    )
+
+    assert not result.errors
+    assert result.data == {"undefinedOptionalsWork": True}

graphene/types/tests/test_type_map.py

@@ -20,8 +20,8 @@ from ..inputobjecttype import InputObjectType
 from ..interface import Interface
 from ..objecttype import ObjectType
 from ..scalars import Int, String
-from ..structures import List, NonNull
 from ..schema import Schema
+from ..structures import List, NonNull
 
 
 def create_type_map(types, auto_camelcase=True):
@@ -227,6 +227,18 @@ def test_inputobject():
     assert foo_field.description == "Field description"
 
 
+def test_inputobject_undefined(set_default_input_object_type_to_undefined):
+    class OtherObjectType(InputObjectType):
+        optional_field = String()
+
+    type_map = create_type_map([OtherObjectType])
+    assert "OtherObjectType" in type_map
+    graphql_type = type_map["OtherObjectType"]
+
+    container = graphql_type.out_type({})
+    assert container.optional_field is Undefined
+
+
 def test_objecttype_camelcase():
     class MyObjectType(ObjectType):
         """Description"""

graphene/validation/depth_limit.py

@@ -30,7 +30,7 @@ try:
 except ImportError:
     # backwards compatibility for v3.6
     from typing import Pattern
-from typing import Callable, Dict, List, Optional, Union
+from typing import Callable, Dict, List, Optional, Union, Tuple
 
 from graphql import GraphQLError
 from graphql.validation import ValidationContext, ValidationRule
@@ -82,7 +82,7 @@ def depth_limit_validator(
 
 
 def get_fragments(
-    definitions: List[DefinitionNode],
+    definitions: Tuple[DefinitionNode, ...],
 ) -> Dict[str, FragmentDefinitionNode]:
     fragments = {}
     for definition in definitions:
@@ -94,7 +94,7 @@ def get_fragments(
 # This will actually get both queries and mutations.
 # We can basically treat those the same
 def get_queries_and_mutations(
-    definitions: List[DefinitionNode],
+    definitions: Tuple[DefinitionNode, ...],
 ) -> Dict[str, OperationDefinitionNode]:
     operations = {}