Cannot access custom resolver powered by AppSync JavaScript resolvers from `backend.data.resources.cfnResources.cfnResolvers`

[fossamagna]

Environment information

System:
  OS: Linux 6.6 Debian GNU/Linux 11 (bullseye) 11 (bullseye)
  CPU: (8) arm64 unknown
  Memory: 14.36 GB / 23.43 GB
  Shell: /bin/bash
Binaries:
  Node: 22.16.0 - /usr/local/bin/node
  Yarn: 1.22.22 - /usr/local/bin/yarn
  npm: 10.9.2 - /usr/local/bin/npm
  pnpm: undefined - undefined
NPM Packages:
  @aws-amplify/auth-construct: 1.8.1
  @aws-amplify/backend: 1.16.1
  @aws-amplify/backend-ai: Not Found
  @aws-amplify/backend-auth: 1.7.1
  @aws-amplify/backend-cli: 1.8.0
  @aws-amplify/backend-data: 1.6.1
  @aws-amplify/backend-deployer: 2.1.3
  @aws-amplify/backend-function: 1.14.1
  @aws-amplify/backend-output-storage: 1.3.1
  @aws-amplify/backend-secret: 1.4.0
  @aws-amplify/backend-storage: 1.4.1
  @aws-amplify/cli-core: 2.2.1
  @aws-amplify/client-config: 1.8.0
  @aws-amplify/data-construct: 1.16.3
  @aws-amplify/data-schema: 1.21.0
  @aws-amplify/deployed-backend-client: 1.8.0
  @aws-amplify/form-generator: 1.2.1
  @aws-amplify/model-generator: 1.2.0
  @aws-amplify/platform-core: 1.10.0
  @aws-amplify/plugin-types: 1.11.0
  @aws-amplify/sandbox: 2.1.2
  @aws-amplify/schema-generator: 1.4.0
  @aws-cdk/toolkit-lib: 1.1.1
  aws-amplify: 6.15.3
  aws-cdk-lib: 2.189.1
  typescript: 5.8.3

Describe the bug

The CfnResolver for the custom query described in the documentation is not included in backend.data.cfnResources.cfnResolvers.
https://docs.amplify.aws/react/build-a-backend/data/custom-business-logic/#step-2---configure-custom-business-logic-handler-code

import {
  type ClientSchema,
  a,
  defineData,
} from '@aws-amplify/backend';

const schema = a.schema({
  Post: a.model({
    content: a.string(),
    likes: a.integer()
      .authorization(allow => [allow.authenticated().to(['read'])])
  }).authorization(allow => [
    allow.owner(),
    allow.authenticated().to(['read'])
  ]),

  likePost: a
    .mutation()
    .arguments({ postId: a.id() })
    .returns(a.ref('Post'))
    .authorization(allow => [allow.authenticated()])
    .handler(a.handler.custom({
      dataSource: a.ref('Post'),
      entry: './increment-like.js'
    }))
});

export type Schema = ClientSchema<typeof schema>;

export const data = defineData({
  schema,
  authorizationModes: {
    defaultAuthorizationMode: 'apiKey',
    apiKeyAuthorizationMode: {
      expiresInDays: 30
    }
  },
});

If we change the handler to a Lambda resolver instead of a JavaScript resolver, it will be included in backend.data.cfnResources.cfnResolvers.

Reproduction steps

1. Deploy the code shown at https://docs.amplify.aws/react/build-a-backend/data/custom-business-logic/#step-2---configure-custom-business-logic-handler-code.
2. Add the following code to backend.ts and verify that the CfnResolver for the AppSync JavaScript resolver is not included in backend.data.cfnResources.cfnResolvers.

   Object.entries(backend.data.resources.cfnResources.cfnResolvers)
     .forEach(([logicalId, resolver]) => {
       console.log(`Resolver found for ${logicalId}: ${resolver}`);
     });

Workaround

Add the following code to backend.ts.

  const resolvers: Record<string, CfnResolver> = {};
  function walkConstructTree(node: IConstruct) {
    if (node instanceof CfnResolver) {
      const logicalId = node.stack.resolve(node.logicalId);
      if (!Object.values(resolvers).includes(node)) {
        const key = logicalId;
        resolvers[key] = node;
      }
    }
    node.node.children.forEach((child) => {
      walkConstructTree(child);
    });
  }
  walkConstructTree(backend.data.stack);

[pahud]

Hi @fossamagna,

Thank you for the detailed report and for providing a working workaround! This appears to be a valid concern regarding the accessibility of JavaScript resolvers through the cfnResources.cfnResolvers API.

After analyzing the code, the issue stems from how JavaScript resolvers are created in the convertJsResolverDefinition function. These resolvers are instantiated directly on the scope rather than being registered with the cfnResources.cfnResolvers collection, which is why they don't appear when you iterate over that property.

The workaround you've provided using construct tree traversal is a solid approach for now. However, this suggests an inconsistency in the API - Lambda resolvers are accessible through cfnResources.cfnResolvers, but JavaScript resolvers are not.

Potential Solution:
The fix would likely involve modifying the convertJsResolverDefinition function to return the created CfnResolver instances and then registering them with the amplifyApi.resources.cfnResources.cfnResolvers collection in the factory.ts file where it's called.