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