Add example of generating an input class

src/scanspec/schema/schema.py

@@ -1,16 +1,75 @@
+from typing import Any
+
 import strawberry
 from fastapi import FastAPI
 from resolvers import reduce_frames, validate_spec
-from specs import Line, PointsResponse
+from specs import PointsResponse
 from strawberry.fastapi import GraphQLRouter
 
 from scanspec.core import Path
+from scanspec.specs import Line, Spec
+
+# Here is the manual version of what we are trying to do
+
+# @strawberry.input
+# class LineInput(Line): ...
+
+
+# @strawberry.input
+# class ZipInput(Zip): ...
+
+
+# @strawberry.input(one_of=True)
+# class SpecInput:
+#     ...
+
+#     line: LineInput | None = strawberry.UNSET
+#     zip: ZipInput | None = strawberry.UNSET
+
+
+def generate_input_class() -> type[Any]:
+    # This will be our input class, we're going to fiddle with it
+    # throughout this function
+    class SpecInput: ...
+
+    # We want to go through all the possible scan specs, this isn't
+    # currently possible but can be implemented.
+    # Raise an issue for a helper function to get all possible scanspec
+    # types.
+    for spec_type in Spec.types:
+        # We make a strawberry input classs using the scanspec pydantic models
+        # This isn't possible because scanspec models are actually pydantic
+        # dataclasses. We should have a word with Tom about it and probably
+        # raise an issue on strawberry.
+        @strawberry.experimental.pydantic.input(all_fields=True, model=spec_type)
+        class InputClass: ...
+
+        # Renaming the class to LineInput, ZipInput etc. so the
+        # schema looks neater
+        InputClass.__name__ = spec_type.__name__ + "Input"
+
+        # Add a field to the class called line, zip etc. and make it
+        # strawberry.UNSET
+        setattr(SpecInput, spec_type.__name__, strawberry.UNSET)
+
+        # Set the type annotation to line | none, zip | none, etc.
+        # Strawberry will read this and graphqlify it.
+        SpecInput.__annotations__[spec_type.__name__] = InputClass | None
+
+    # This is just a programtic equivalent of
+    # @strawberry.input(one_of=True)
+    # class SpecInput:
+    #    ...
+    return strawberry.input(one_of=True)(SpecInput)
+
+
+SpecInput = generate_input_class()
 
 
 @strawberry.type
 class Query:
     @strawberry.field
-    def validate(self, spec: Line) -> str:
+    def validate(self, spec: SpecInput) -> str:
         return validate_spec(spec)
 
     @strawberry.field