added example of #190

Author: Code-Hex

example/zod/README.md

@@ -8,4 +8,70 @@ You can use zod [extend API](https://github.com/colinhacks/zod#extend).
 const AttributeInputSchemaWithCUID = AttributeInputSchema().extend({
   key: z.string().cuid(),
 });
+```
+
+## Apply input validator via ts decorator
+
+Validate the input object via typescript decorators when implementing resolvers. See: #190
+
+### Usage
+
+```ts
+class Mutation {
+  @validateInput(SignupInputSchema)
+  async signup(
+    _root: Record<string, never>,
+    { input: { email, password } }: MutationSignupArgs,
+    context: Context
+  ): Promise<SignupPayload> {
+    // The input here is automatically valid to adhere to SignupInputSchema
+  }
+}
+```
+
+### Implementation:
+
+```ts
+type ZodResolver<T extends ZodType<any, any, any>> = ResolverFn<
+  any,
+  any,
+  any,
+  { input: TypeOf<T> }
+>
+
+/**
+ * Method decorator that validates the argument of the target function against the given schema.
+ *
+ * @export
+ * @template T The type of the zod schema.
+ * @param {T} arg The zod schema used for the validation.
+ * @return {MethodDecorator} A {@link MethodDecorator}.
+ */
+export function validateInput<T extends AnyZodObject>(
+  arg: T | (() => T)
+): MethodDecorator<ZodResolver<T>> {
+  return function (_target, _propertyKey, descriptor) {
+    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+    const originalMethod = descriptor.value!
+    // @ts-expect-error: should be fine
+    descriptor.value = function (root, { input }, context, info) {
+      const schema = typeof arg === 'function' ? arg() : arg
+      const result = schema.safeParse(input)
+
+      if (result.success) {
+        // eslint-disable-next-line @typescript-eslint/no-unsafe-return
+        return originalMethod.call(
+          this,
+          root,
+          { input: result.data },
+          context,
+          info
+        )
+      } else {
+        return { problems: result.error.issues }
+      }
+    }
+    return descriptor
+  }
+}
 ```