使用Dynamo Db在AWS Appsync中执行批处理获取故障

Question

I have trouble executing Batch Get in app sync. This is my following resolvers.

Request mapping template.

#set($ids = [])
#foreach($id in ${ctx.args.topicIds})
   #set($map = {})
   $util.qr($map.put("topicId", $util.dynamodb.toString($id)))
   $util.qr($ids.add($map))
#end

{
 "version" : "2018-05-29",
 "operation" : "BatchGetItem",
 "tables" : {
    "Topic": {
        "keys": $util.toJson($ids),
        "consistentRead": true
    }
 }
}

Response Mapping Template

$util.toJson($ctx.result.data.Topic)

This is how I give the query

 query listStudentBookmarkedTopics {
   listStudentBookmarkedTopics(
     topicIds: [ "503", "501" ]
   ) {
     topicId
   }
 }

But I am getting null results

 {
  "data": {
    "listStudentBookmarkedTopics": [
      null,
      null
    ] 
  }
}

This is how my table looks like

This is Cloud watch logs

Answer 1

what does your DynamoDB Table look like? Is Topic the name of the table? What is the primary partition key defined on it? I need additional details to help you with this.

Alternatively, please turn on CloudWatch logs for your API (you should be able to do this via Console -> under Settings page for your API). Try to run your query again, and see what is the resolved Request and Response templates for this path. That should provide you additional details.

Answer 2

I had a similar problem. Fixed it by applying appropriate permissions. If you created new IAM role it doesn't grant batch* permissions by default. From AWS docs:

Like other resolvers, you need to create a data source in AWS AppSync and either create a role or use an existing one. Because batch operations require different permissions on DynamoDB tables, you need to grant the configured role permissions for read or write actions:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": [
        "dynamodb:BatchGetItem",
        "dynamodb:BatchWriteItem"
      ],
      "Effect": "Allow",
      "Resource": [
        "arn:aws:dynamodb:region:account:table/TABLENAME",
        "arn:aws:dynamodb:region:account:table/TABLENAME/*"
      ]
    }
  ]
}

You either can attach a new policy or just add "dynamodb:BatchGetItem" on existing one in IAM dashboard. `