Question

我有传感器每4秒向DynamoDB表发送数据，我想只检索特定传感器的最新值。表中的主键是传感器ID和SysDt时间戳。我已指定一个索引，将传感器ID用作分区键，使用GWID（网关ID）作为排序键。我无法仅从表中检索最新值。

这是我的剧本：

    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);
            }
        });
    }

我已阅读this，但我无法弄清楚如何去做。

我感谢你的帮助。

Answer 1

我能够弄清楚，所以我想把它张贴在这里给任何寻找答案的人。

我定义params的方式不正确。这是有效的Javascript代码：

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);
        }
    });
}

从DynamoDB表获取最新值

1 个答案: