Add support for optional arguments when a default value is provided (#82

)

* added support for optional arguments when a default value is provided

* fixed no default arguments case

* Switched default argument detection to use inspect.signature, added tests for default arguments with custom types

* added release info

RELEASE.md

@@ -0,0 +1,18 @@
+Release type: minor
+
+Added support for optional fields with default arguments in the GraphQL schema when default arguments are passed to the resolver.
+
+Example:
+ ```python
+@strawberry.type
+class Query:
+    @strawberry.field
+    def hello(self, info, name: str = "world") -> str:
+        return name
+```
+
+```graphql
+type Query {
+    hello(name: String = "world"): String
+}
+```

strawberry/field.py

@@ -1,3 +1,4 @@
+import inspect
 import typing
 
 import dataclasses
@@ -202,6 +203,7 @@ def _get_field(
     name = wrap.__name__
 
     annotations = typing.get_type_hints(wrap, None, REGISTRY)
+    parameters = inspect.signature(wrap).parameters
     field_type = get_graphql_type_for_annotation(annotations["return"], name)
 
     arguments_annotations = {
@@ -211,7 +213,9 @@ def _get_field(
     }
 
     arguments = {
-        to_camel_case(name): get_graphql_type_for_annotation(annotation, name)
+        to_camel_case(name): get_graphql_type_for_annotation(
+            annotation, name, parameters[name].default != inspect._empty
+        )
         for name, annotation in arguments_annotations.items()
     }
 

tests/test_field.py

@@ -1,7 +1,12 @@
 import pytest
 
 import strawberry
-from graphql import GraphQLField, GraphQLNonNull
+from graphql import (
+    GraphQLField,
+    GraphQLInputObjectType,
+    GraphQLNonNull,
+    GraphQLScalarType,
+)
 from strawberry.exceptions import (
     MissingArgumentsAnnotationsError,
     MissingReturnAnnotationError,
@@ -29,6 +34,48 @@ def hello(self, info, id: int) -> str:
     assert hello.field.args["id"].type.of_type.name == "Int"
 
 
+def test_field_default_arguments_are_optional():
+    @strawberry.field
+    def hello(self, info, test: int, id: int = 1, asdf: str = "hello") -> str:
+        return "I'm a resolver"
+
+    assert hello.field
+
+    assert type(hello.field) == GraphQLField
+    assert type(hello.field.type) == GraphQLNonNull
+    assert hello.field.type.of_type.name == "String"
+
+    assert type(hello.field.args["id"].type) == GraphQLScalarType
+    assert hello.field.args["id"].type.name == "Int"
+
+    assert type(hello.field.args["asdf"].type) == GraphQLScalarType
+    assert hello.field.args["asdf"].type.name == "String"
+
+
+def test_field_default_optional_argument_custom_type():
+    @strawberry.input
+    class CustomInputType:
+        field: str
+
+    @strawberry.field
+    def hello(
+        self, info, required: CustomInputType, optional: CustomInputType = None
+    ) -> str:
+        return "I'm a resolver"
+
+    assert hello.field
+
+    assert type(hello.field) == GraphQLField
+    assert type(hello.field.type) == GraphQLNonNull
+    assert hello.field.type.of_type.name == "String"
+
+    assert type(hello.field.args["required"].type) == GraphQLNonNull
+    assert hello.field.args["required"].type.of_type.name == "CustomInputType"
+
+    assert type(hello.field.args["optional"].type) == GraphQLInputObjectType
+    assert hello.field.args["optional"].type.name == "CustomInputType"
+
+
 def test_raises_error_when_return_annotation_missing():
     with pytest.raises(MissingReturnAnnotationError) as e: