feat(appsync): set max batch size when using batch invoke (#20995)

closes #20467

----

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### Adding new Unconventional Dependencies:

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### New Features

* [x] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [x] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-appsync/lib/resolver.ts

@@ -45,6 +45,12 @@ export interface BaseResolverProps {
    * @default - No caching configuration
    */
   readonly cachingConfig?: CachingConfig;
+  /**
+   * The maximum number of elements per batch, when using batch invoke
+   *
+   * @default - No max batch size
+   */
+  readonly maxBatchSize?: number;
 }
 
 /**
@@ -112,6 +118,7 @@ export class Resolver extends Construct {
       requestMappingTemplate: props.requestMappingTemplate ? props.requestMappingTemplate.renderTemplate() : undefined,
       responseMappingTemplate: props.responseMappingTemplate ? props.responseMappingTemplate.renderTemplate() : undefined,
       cachingConfig: this.createCachingConfig(props.cachingConfig),
+      maxBatchSize: props.maxBatchSize,
     });
     props.api.addSchemaDependency(this.resolver);
     if (props.dataSource) {

packages/@aws-cdk/aws-appsync/test/appsync-mapping-template.test.ts

@@ -57,12 +57,14 @@ describe('Lambda Mapping Templates', () => {
       fieldName: 'relatedPosts',
       requestMappingTemplate: appsync.MappingTemplate.lambdaRequest('$util.toJson($ctx)', 'BatchInvoke'),
       responseMappingTemplate: appsync.MappingTemplate.lambdaResult(),
+      maxBatchSize: 10,
     });
 
     // THEN
     Template.fromStack(stack).hasResourceProperties('AWS::AppSync::Resolver', {
       FieldName: 'relatedPosts',
       RequestMappingTemplate: batchMT,
+      MaxBatchSize: 10,
     });
   });
 });

packages/@aws-cdk/aws-appsync/test/appsync.lambda.graphql

@@ -21,4 +21,5 @@ type Post {
     ups: Int
     downs: Int
     relatedPosts: [Post]
+    relatedPostsMaxBatchSize: [Post]
 }

packages/@aws-cdk/aws-appsync/test/integ.appsync-lambda.ts

@@ -67,12 +67,20 @@ lambdaDS.createResolver({
   requestMappingTemplate: appsync.MappingTemplate.lambdaRequest(requestPayload('addPost', { withArgs: true })),
   responseMappingTemplate,
 });
+
 lambdaDS.createResolver({
   typeName: 'Post',
   fieldName: 'relatedPosts',
   requestMappingTemplate: appsync.MappingTemplate.lambdaRequest(requestPayload('relatedPosts', { withSource: true }), 'BatchInvoke'),
   responseMappingTemplate,
 });
 
+lambdaDS.createResolver({
+  typeName: 'Post',
+  fieldName: 'relatedPostsMaxBatchSize',
+  requestMappingTemplate: appsync.MappingTemplate.lambdaRequest(requestPayload('relatedPostsMaxBatchSize', { withSource: true }), 'BatchInvoke'),
+  responseMappingTemplate,
+  maxBatchSize: 2,
+});
 
 app.synth();

packages/@aws-cdk/aws-appsync/test/verify.integ.appsync-lambda.sh

@@ -21,7 +21,7 @@ elif [[ "$1" == "--check" ]]; then
     exit 1
   fi
   echo THIS TEST SHOULD PRODUCE A LIST OF BOOKS
-  curl -XPOST -H "Content-Type:application/graphql" -H "x-api-key:$2" -d '{ "query": "query { allPosts { id author title relatedPosts { id title } } }" }" }' $3 | json_pp
+  curl -XPOST -H "Content-Type:application/graphql" -H "x-api-key:$2" -d '{ "query": "query { allPosts { id author title relatedPosts { id title } relatedPostsMaxBatchSize { id title } } }" }" }' $3 | json_pp
   echo ""
 elif [[ "$1" == "--clean" ]];then
   cdk destroy --app "node integ.appsync-lambda.js"

packages/@aws-cdk/aws-appsync/test/verify/lambda-tutorial/lambda-tutorial.js

@@ -19,6 +19,7 @@ exports.handler = (event, context, callback) => {
     console.log("Got an BatchInvoke Request. The payload has %d items to resolve.", event.length);
     const field = event[0].field;
     switch(field) {
+      case "relatedPostsMaxBatchSize":
       case "relatedPosts":
         var results = [];
         // the response MUST contain the same number