AWS Lambda update DynamoDB item

Question

I have a DynamoDB table called Wishlist, and an existing DynamoDB Item which I'm calling "monitor".

I am trying to write a Lambda function that updates the "monitor" item as follows:

takes the user's login ID, appends @gmail.com to it, and writes it to a new email attribute
writes a timestamp to the item

Here is my code:

console.log('Loading function');
var doc = require('dynamodb-doc');
var db = new doc.DynamoDB();

exports.handler = function(event, context) 
{
     var username  = event.username;
     var email = event.username+"@gmail.com";
     console.log(username + "," + email);

     var tableName = "WishList";
     var item = {
           "username":username,
           "email":  email,     
     };

     var params = {
         TableName:tableName, 
         Item: item
     };

     console.log(params);
     db.putItem(params, function(err,data){
         if (err) console.log(err);
         else console.log(data);
     });
};

How do I read the existing "monitor" item so that I can update it with putItem?

What is the primary key of the table?

Mark B
– Mark B

2017-11-13 23:45:38 +00:00
Commented Nov 13, 2017 at 23:45 — Mark B
– Mark B, Commented Nov 13, 2017 at 23:45
Primary partition key - Device (String) @MarkB

Craig A Gomez
– Craig A Gomez

2017-11-14 00:04:05 +00:00
Commented Nov 14, 2017 at 0:04 — Craig A Gomez
– Craig A Gomez, Commented Nov 14, 2017 at 0:04

jarmod · Accepted Answer · 2017-11-14 00:28:49Z

2

If I understand your question, you need to:

get the existing item by its key using getItem
modify the returned item
put the modified item using putItem

Alternatively, you can simply use updateItem which will edit an existing item's attributes, or add a new item to the table if it does not already exist.

You can see sample code here.

answered Nov 14, 2017 at 0:28

jarmod

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