Getting the latest value from DynamoDB table

Question

I have sensors sending data to the DynamoDB table every 4 seconds and I want to retrieve only the latest value of a particular sensor. The primary keys in the table are sensor ID and SysDt time stamp. I have specified an index to use sensor ID as Partition Key and GWID (Gateway ID) as the Sort Key. I am unable to retrieve only the latest values from the table.

This is my script:

    AWS.config.update({
      region: "us-west-2",
      endpoint: 'https://dynamodb.us-west-2.amazonaws.com',
      accessKeyId: "Fakeaccesskey",
      secretAccessKey: "Fakesecretkey"
    });

    var docClient = new AWS.DynamoDB.DocumentClient();

    function readItemtesttwovalues() {
        var table = "TA_Log1";
        var indexidgwid = "ID-GWID-index";
        var ID = "BB00000013";
        var GWID = "AA00000001";


        var params = {
            TableName: table,
            IndexName: indexidgwid,
            Key:{
                "ID": ID,
                "GWID": GWID
            },
            ScanIndexForward: false,
            Limit: 1
        };
        docClient.query(params, function(err, data) {
            if (err) {
                document.getElementById('testtwostatus').innerHTML = "Unable to read item: " + "\n" + JSON.stringify(err, undefined, 2);
            } else {
                document.getElementById('testtwostatus').innerHTML = data.Item.Status;
                document.getElementById('testtwotemp').innerHTML = data.Item.Temp;
                document.getElementById('testtwotempmap').innerHTML = data.Item.Temp;
                document.getElementById('testtwohum').innerHTML = data.Item.Hum;
                document.getElementById('testtwohummap').innerHTML = data.Item.Hum;
                document.getElementById('testtwobat').innerHTML = data.Item.BatV;
                document.getElementById('testtwobatmap').innerHTML = data.Item.BatV;
                var temp = Number(data.Item.Temp);
            }
        });
    }

I have read this but I am unable to figure out how to go about it.

I thank you for your help.

score 1 · Accepted Answer · answered Jun 21 '18 at 05:38

I was able to figure it out so thought I'd post it here for anyone looking for the answer.

The way I had defined the params was incorrect. Here is the Javascript code that works:

AWS.config.update({
  region: "us-west-2",
  endpoint: 'https://dynamodb.us-west-2.amazonaws.com',
  accessKeyId: "Fakeaccesskey",
  secretAccessKey: "Fakesecretkey"
});

var docClient = new AWS.DynamoDB.DocumentClient();

function readItemtesttwovalues() {

    var params = {
        TableName: "TA_Log1",
        IndexName: "ID-GWID-index",
        KeyConditionExpression: "ID = :id and GWID = :gwid",
        ExpressionAttributeValues: {
            ":id": "BB00000013",
            ":gwid": "AA00000001"
        },
        ScanIndexForward: false,
        Limit: 1
    };
    docClient.query(params, function(err, data) {
        if (err) {
            document.getElementById('testtwostatus').innerHTML = "Unable to read item: " + "\n" + JSON.stringify(err, undefined, 2);
        } else {
            document.getElementById('testtwostatus').innerHTML = data.Item.Status;
            document.getElementById('testtwotemp').innerHTML = data.Item.Temp;
            document.getElementById('testtwotempmap').innerHTML = data.Item.Temp;
            document.getElementById('testtwohum').innerHTML = data.Item.Hum;
            document.getElementById('testtwohummap').innerHTML = data.Item.Hum;
            document.getElementById('testtwobat').innerHTML = data.Item.BatV;
            document.getElementById('testtwobatmap').innerHTML = data.Item.BatV;
            var temp = Number(data.Item.Temp);
        }
    });
}

Getting the latest value from DynamoDB table

1 Answers1