DynamoDB Put Operation Doesn't Return the Data Inserted

5/19/2018

This is something that tripped me up a little bit when I was recently playing around with DynamoDB. I was very confused because in the callback function the data argument was just coming back as an empty object. "Surely that can't be right", I thought, but indeed it was right!

Some Code

Here I have a snippet of some Node.js code that puts some data into DynamoDB. This code does work in that it actually puts stuff into the DynamoDB table, but at the end it logs, "got some data: {}".

const AWS = require('aws-sdk')
const docClient = new AWS.DynamoDB.DocumentClient({ region: 'eu-central-1' })

const createDocument = (text, callback) => {
  const createParams = {
    Item: {
      text: text
    },
    TableName: 'ToDoItems'
  }

  docClient.put(createParams, (err, data) => {
    if(err) {
          console.log('uh oh! ', err);
    } else {
          console.log('put some data: ', data);
    }
  })
}

Some Answers

After some Googling I stumbled upon this stack overflow question. The OP was asking the exact question I had. In the first answer I can see that I needed to add the ReturnValues property to my query object. However, in the answer we see that 'ALL_NEW' is not even an option for ReturnValues when doing a put operation! The third answer here is also pretty interesting. In this solution we use an overall update operation that contains many PUT actions- pretty clever.

const createParams = { 
  TableName: "table",
      Key: {
          id: randomId
      },
      AttributeUpdates: {
          authorId: {Action: "PUT", Value: event.authorId},
          date: {Action: "PUT", Value: event.date},
          description: {Action: "PUT", Value: event.description},
          title: {Action: "PUT", Value: event.title}
      },
      ReturnValues: "ALL_NEW"
}

Know Whatcha Got

The key to choosing the correct command for the task at hand is to know what's available to you. That means understanding how the basic CRUD (create, read, update, delete) operations work in DynamoDB but also being aware of Dynamo-specific things like working with change streams or commands for managing an entire table a time (here's a really useful "HowItWorks" dynamoDB Api docs page). As a coder you've got to love learning because there will always be a useful library you haven't touched yet that could make your and your projects that much better. Don't be afraid. Just dive straight in!

0 Comments