Add new strawberry.Parent annotation to support static resolvers with…

… non-self types. (#3017)

RELEASE.md

@@ -0,0 +1,26 @@
+Release type: minor
+
+Adds new strawberry.Parent type annotation to support resolvers without use of self.
+
+E.g.
+
+```python
+@dataclass
+class UserRow:
+    id_: str
+
+
+@strawberry.type
+class User:
+    @strawberry.field
+    @staticmethod
+    async def name(parent: strawberry.Parent[UserRow]) -> str:
+        return f"User Number {parent.id}"
+
+
+@strawberry.type
+class Query:
+    @strawberry.field
+    def user(self) -> User:
+        return UserRow(id_="1234")
+```

docs/errors/conflicting-arguments.md

@@ -0,0 +1,26 @@
+---
+title: Conflicting Arguments Error
+---
+
+# Conflicting Arguments Error
+
+## Description
+
+This error is thrown when you define a resolver with multiple arguments that
+conflict with each other, like "self", "root", or any arguments annotated with
+strawberry.Parent.
+
+For example the following code will throw this error:
+
+```python
+import strawberry
+
+
+@strawberry.type
+class Query:
+    @strawberry.field
+    def hello(
+        self, root, parent: strawberry.Parent[str]
+    ) -> str:  #  <-- self, root, and parent all identify the same input
+        return f"hello world"
+```

docs/types/resolvers.md

@@ -222,6 +222,50 @@ class User:
     full_name: str = strawberry.field(resolver=full_name)
 ```
 
+For either decorated resolvers or Python functions, there is a third option
+which is to annotate one of the parameters with the type `Parent`. This is
+particularly useful if the parent resolver returns a type other than the
+strawberry type that the resolver is defined within, as it allows you to
+specify the type of the parent object. This comes up particularly often
+for resolvers that return ORMs:
+
+```python
+import dataclass
+
+import strawberry
+
+
+@dataclass
+class UserRow:
+    id_: str
+
+
+@strawberry.type
+class User:
+    @strawberry.field
+    @staticmethod
+    async def name(parent: strawberry.Parent[UserRow]) -> str:
+        return f"User Number {parent.id}"
+
+
+@strawberry.type
+class Query:
+    @strawberry.field
+    def user(self) -> User:
+        # Even though this method is annotated as returning type `User`,
+        # which strawberry uses to define the GraphQL schema, we're
+        # not actually required to return an object of that type. Whatever
+        # object we do return will be passed on to child resolvers that
+        # request it via the `self`, `root`, or `strawberry.Parent` parameter.
+        # In this case, we return our ORM directly.
+        #
+        # Put differently, the GraphQL schema and associated resolvers come
+        # from the type annotations, but the actual object passed to the
+        # resolvers via `self`, `root`, or `strawberry.Parent` is whatever
+        # the parent resolvers return, regardless of type.
+        return UserRow(id_="1234")
+```
+
 ## Accessing execution information
 
 Sometimes it is useful to access the information for the current execution

strawberry/__init__.py

@@ -8,6 +8,7 @@
 from .lazy_type import LazyType, lazy
 from .mutation import mutation, subscription
 from .object_type import asdict, input, interface, type
+from .parent import Parent
 from .permission import BasePermission
 from .private import Private
 from .scalars import ID
@@ -23,6 +24,7 @@
     "UNSET",
     "lazy",
     "LazyType",
+    "Parent",
     "Private",
     "Schema",
     "argument",

strawberry/exceptions/__init__.py

@@ -5,6 +5,7 @@
 
 from graphql import GraphQLError
 
+from .conflicting_arguments import ConflictingArgumentsError
 from .duplicated_type_name import DuplicatedTypeName
 from .exception import StrawberryException, UnableToFindExceptionSource
 from .handler import setup_exception_handler
@@ -178,6 +179,7 @@ class StrawberryGraphQLError(GraphQLError):
     "WrongNumberOfResultsReturned",
     "FieldWithResolverAndDefaultValueError",
     "FieldWithResolverAndDefaultFactoryError",
+    "ConflictingArgumentsError",
     "MissingQueryError",
     "InvalidArgumentTypeError",
     "InvalidDefaultFactoryError",

strawberry/exceptions/conflicting_arguments.py

@@ -0,0 +1,54 @@
+from __future__ import annotations
+
+from functools import cached_property
+from typing import TYPE_CHECKING, List, Optional
+
+from .exception import StrawberryException
+from .utils.source_finder import SourceFinder
+
+if TYPE_CHECKING:
+    from strawberry.types.fields.resolver import StrawberryResolver
+
+    from .exception_source import ExceptionSource
+
+
+class ConflictingArgumentsError(StrawberryException):
+    def __init__(
+        self,
+        resolver: StrawberryResolver,
+        arguments: List[str],
+    ):
+        self.function = resolver.wrapped_func
+        self.argument_names = arguments
+
+        self.message = (
+            f"Arguments {self.argument_names_str} define conflicting resources. "
+            "Only one of these arguments may be defined per resolver."
+        )
+
+        self.rich_message = self.message
+
+        self.suggestion = (
+            f"Only one of {self.argument_names_str} may be defined per resolver."
+        )
+
+        self.annotation_message = self.suggestion
+
+    @cached_property
+    def argument_names_str(self) -> str:
+        return (
+            ", ".join(f'"{name}"' for name in self.argument_names[:-1])
+            + " and "
+            + f'"{self.argument_names[-1]}"'
+        )
+
+    @cached_property
+    def exception_source(self) -> Optional[ExceptionSource]:
+        if self.function is None:
+            return None  # pragma: no cover
+
+        source_finder = SourceFinder()
+
+        return source_finder.find_argument_from_object(
+            self.function, self.argument_names[1]  # type: ignore
+        )

strawberry/exceptions/utils/source_finder.py

@@ -50,7 +50,7 @@ def find_source(self, module: str) -> Optional[SourcePath]:
         if not path.exists() or path.suffix != ".py":
             return None  # pragma: no cover
 
-        source = path.read_text()
+        source = path.read_text(encoding="utf-8")
 
         return SourcePath(path=path, code=source)
 

strawberry/parent.py

@@ -0,0 +1,39 @@
+from typing import TypeVar
+from typing_extensions import Annotated
+
+
+class StrawberryParent:
+    ...
+
+
+T = TypeVar("T")
+
+Parent = Annotated[T, StrawberryParent()]
+Parent.__doc__ = """Represents a parameter holding the parent resolver's value.
+
+This can be used when defining a resolver on a type when the parent isn't expected
+to return the type itself.
+
+Example:
+
+>>> import strawberry
+>>> from dataclasses import dataclass
+>>>
+>>> @dataclass
+>>> class UserRow:
+...     id_: str
+...
+>>> @strawberry.type
+... class User:
+...     @strawberry.field
+...     @staticmethod
+...     async def name(parent: strawberry.Parent[UserRow]) -> str:
+...         return f"User Number {parent.id}"
+...
+>>> @strawberry.type
+>>> class Query:
+...     @strawberry.field
+...     def user(self) -> User:
+...         return UserRow(id_="1234")
+...
+"""

strawberry/private.py

@@ -1,5 +1,7 @@
 from typing import TypeVar
-from typing_extensions import Annotated, get_args, get_origin
+from typing_extensions import Annotated
+
+from strawberry.utils.typing import type_has_annotation
 
 
 class StrawberryPrivate:
@@ -22,9 +24,4 @@ class StrawberryPrivate:
 
 
 def is_private(type_: object) -> bool:
-    if get_origin(type_) is Annotated:
-        return any(
-            isinstance(argument, StrawberryPrivate) for argument in get_args(type_)
-        )
-
-    return False
+    return type_has_annotation(type_, StrawberryPrivate)

strawberry/schema/schema_converter.py

@@ -574,7 +574,7 @@ def _get_arguments(
             # the following code allows to omit info and root arguments
             # by inspecting the original resolver arguments,
             # if it asks for self, the source will be passed as first argument
-            # if it asks for root, the source it will be passed as kwarg
+            # if it asks for root or parent, the source will be passed as kwarg
             # if it asks for info, the info will be passed as kwarg
 
             args = []
@@ -583,12 +583,13 @@ def _get_arguments(
                 if field.base_resolver.self_parameter:
                     args.append(source)
 
-                root_parameter = field.base_resolver.root_parameter
-                if root_parameter:
+                if parent_parameter := field.base_resolver.parent_parameter:
+                    kwargs[parent_parameter.name] = source
+
+                if root_parameter := field.base_resolver.root_parameter:
                     kwargs[root_parameter.name] = source
 
-                info_parameter = field.base_resolver.info_parameter
-                if info_parameter:
+                if info_parameter := field.base_resolver.info_parameter:
                     kwargs[info_parameter.name] = info
 
             return args, kwargs