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Scan DynamoDB Items With Node.js

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Scan DynamoDB Items With Node.js

Tap into DynamoDB's scanning ability with some quick JavaScript. Be warned, though, that it might be more expensive than it's worth.

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In previous posts, we covered how to query a DynamoDB database.

Query DynamoDB Part 1.
Query DynamoDB Part 2.

Apart from issuing queries DynamoDB, also offers Scan functionality. 

Scan fetches all the items you might have on your DynamoDB Table. Therefore, scan does not require any rules based on your partition key or your global/local secondary indexes. What scan offers is filtering based on the items already fetched and returning specific attributes from those fetched items.

The snippet below issues a scan on the Logins table by adding filtering and selecting only the email field:

var scanLogins = function(date,callback) {

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

        var params = {
            TableName:"Logins",
            ProjectionExpression: "email",
            FilterExpression: "#timestamp < :from",
            ExpressionAttributeNames: {
                "#timestamp": "timestamp",
            },
            ExpressionAttributeValues: {
                ":from": date.getTime()
            }
    };

    var items = []

    var scanExecute = function(callback) {

        docClient.scan(params,function(err,result) {

            if(err) {
                callback(err);
            } else {

                items = items.concat(result.Items);

                if(result.LastEvaluatedKey) {

                    params.ExclusiveStartKey = result.LastEvaluatedKey;
                    scanExecute(callback);
                } else {
                    callback(err,items);
                }
            }
        });
    }
    scanExecute(callback);
};


Before using scan on an application, we have to take into consideration that scan fetches all table items. Therefore, it has a high cost both on charges and performance. Also, it might consume your provision capacity. It is better to stick to queries and avoid scans.

You can find the source code on GitHub.

Related Refcard:

Learn how the world’s first NoSQL Engagement Database delivers unparalleled performance at any scale for customer experience innovation that never ends.

Topics:
database ,partition ,query ,indexes ,dynamodb ,key ,table

Published at DZone with permission of Emmanouil Gkatziouras, DZone MVB. See the original article here.

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