{
    "version" : "2017-02-28",
    "operation" : "Query",
    "query" : {
        "expression": "sender = :id",
        "expressionValues" : {
            ":id" : {
                "S" : "${context.source.cognitoId}"
            }
        }
    },
    "index": "sender-conversationId-index",
    "scanIndexForward": false,
    "limit": #if(${context.arguments.first}) ${context.arguments.first} #else 20 #end,
    "nextToken": #if(${context.arguments.after}) "${context.arguments.after}" #else null #end
}