Increment an Atomic Counter

Disclaimer: This is not an original writing. I am just summarizing from here

What is an atomic counter?

you use the update method to increment or decrement the value of an existing attribute without interfering with other write requests. This method is called an atomic counter

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var AWS = require("aws-sdk");

AWS.config.update({
  region: "us-west-2",
  endpoint: "http://localhost:8000"
});

var docClient = new AWS.DynamoDB.DocumentClient()

var table = "Movies";

var year = 2015;
var title = "The Big New Movie";

// Increment an atomic counter

var params = {
    TableName:table,
    Key:{
        "year": year,
        "title": title
    },
    UpdateExpression: "set info.rating = info.rating + :val",
    ExpressionAttributeValues:{
        ":val": 1
    },
    ReturnValues:"UPDATED_NEW"
};

console.log("Updating the item...");
docClient.update(params, function(err, data) {
    if (err) {
        console.error("Unable to update item. Error JSON:", JSON.stringify(err, null, 2));
    } else {
        console.log("UpdateItem succeeded:", JSON.stringify(data, null, 2));
    }
});

Notice the value from ExpressionAttributeValues and UpdateExpression. They are being incremented by value of the value in expressionAttributeValues where above is by 1. You can change the value by inputting value by yourself.