Sketch an idea of what Grats could do for schema directives

examples/production-app/graphql/directives.ts

@@ -1,45 +1,31 @@
-import { defaultFieldResolver, GraphQLError, GraphQLSchema } from "graphql";
+import {
+  defaultFieldResolver,
+  GraphQLError,
+  GraphQLFieldConfig,
+} from "graphql";
 import { Int } from "grats";
 import { Ctx } from "../ViewerContext";
-import { getDirective, MapperKind, mapSchema } from "@graphql-tools/utils";
 
 /**
  * Some fields cost credits to access. This directive specifies how many credits
  * a given field costs.
  *
- * @gqlDirective cost on FIELD_DEFINITION
+ * @gqlDirective
  */
-export function debitCredits(args: { credits: Int }, context: Ctx): void {
-  if (context.credits < args.credits) {
-    // Using `GraphQLError` here ensures the error is not masked by Yoga.
-    throw new GraphQLError(
-      `Insufficient credits remaining. This field cost ${args.credits} credits.`,
-    );
-  }
-  context.credits -= args.credits;
-}
-
-type CostArgs = { credits: Int };
-
-// Monkey patches the `resolve` function of fields with the `@cost` directive
-// to deduct credits from the user's account when the field is accessed.
-export function applyCreditLimit(schema: GraphQLSchema): GraphQLSchema {
-  return mapSchema(schema, {
-    [MapperKind.OBJECT_FIELD]: (fieldConfig) => {
-      const costDirective = getDirective(schema, fieldConfig, "cost", [
-        "grats",
-        "directives",
-      ]);
-      if (costDirective == null || costDirective.length === 0) {
-        return fieldConfig;
-      }
-
-      const originalResolve = fieldConfig.resolve ?? defaultFieldResolver;
-      fieldConfig.resolve = (source, args, context, info) => {
-        debitCredits(costDirective[0] as CostArgs, context);
-        return originalResolve(source, args, context, info);
-      };
-      return fieldConfig;
-    },
-  });
+export function cost<T>(
+  field: GraphQLFieldConfig<T, Ctx>,
+  credits: Int,
+): GraphQLFieldConfig<T, Ctx> {
+  const originalResolve = field.resolve ?? defaultFieldResolver;
+  field.resolve = (source, resolverArgs, context, info) => {
+    if (context.credits < credits) {
+      // Using `GraphQLError` here ensures the error is not masked by Yoga.
+      throw new GraphQLError(
+        `Insufficient credits remaining. This field cost ${credits} credits.`,
+      );
+    }
+    context.credits -= credits;
+    return originalResolve(source, resolverArgs, context, info);
+  };
+  return field;
 }

examples/production-app/schema.ts

@@ -12,6 +12,7 @@ import { createLike as mutationCreateLikeResolver } from "./models/Like";
 import { createPost as mutationCreatePostResolver } from "./models/Post";
 import { createUser as mutationCreateUserResolver } from "./models/User";
 import { GraphQLSchema, GraphQLDirective, DirectiveLocation, GraphQLNonNull, GraphQLInt, GraphQLObjectType, GraphQLList, GraphQLString, GraphQLScalarType, GraphQLID, GraphQLInterfaceType, GraphQLBoolean, GraphQLInputObjectType } from "graphql";
+import { cost } from "./graphql/directives";
 export function getSchema(): GraphQLSchema {
     const DateType: GraphQLScalarType = new GraphQLScalarType({
         description: "A date and time. Serialized as a Unix timestamp.\n\n**Note**: The `@specifiedBy` directive does not point to a real spec, but is\nincluded here for demonstration purposes.",
@@ -54,7 +55,7 @@ export function getSchema(): GraphQLSchema {
                         return postIdResolver(source);
                     }
                 },
-                likes: {
+                likes: cost({
                     description: "All the likes this post has received.\n**Note:** You can use this connection to access the number of likes.",
                     name: "likes",
                     type: LikeConnectionType,
@@ -72,20 +73,10 @@ export function getSchema(): GraphQLSchema {
                             type: GraphQLInt
                         }
                     },
-                    extensions: {
-                        grats: {
-                            directives: [{
-                                    name: "cost",
-                                    args: {
-                                        credits: 10
-                                    }
-                                }]
-                        }
-                    },
                     resolve(source, args, _context, info) {
                         return source.likes(args, info);
                     }
-                },
+                }, {credits: 10}),
                 publishedAt: {
                     description: "The date and time at which the post was created.",
                     name: "publishedAt",

examples/production-app/server.ts

@@ -4,10 +4,8 @@ import { getSchema } from "./schema";
 import { VC } from "./ViewerContext";
 import { addGraphQLScalarSerialization } from "./graphql/CustomScalars";
 import { useDeferStream } from "@graphql-yoga/plugin-defer-stream";
-import { applyCreditLimit } from "./graphql/directives";
 
 let schema = getSchema();
-schema = applyCreditLimit(schema);
 schema = addGraphQLScalarSerialization(schema);
 
 const yoga = createYoga({