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13 DynamoDB Node.js (DocumentClient) Query Examples

Written by Rafal Wilinski

DynamoDB Node.js Query Examples

This cheat sheet should help you how to perform basic query operations with DynamoDB and Node.JS

There are two basic ways to interact with DynamoDB tables from Node.js applications:

  • Class AWS.DynamoDB from AWS SDK for JavaScript
  • AWS.DynamoDB.DocumentClient which simplifies working with DynamoDB items by abstracting away DynamoDB Types and converting responses to native JS

This cheat sheet will mostly focus on DocumentClient but some of the operations like creating tables must be run using classical DynamoDB service.

If you're looking for similar cheat sheet but for Python, you can find it here

Table of Contents

Setup

Setting up your Node.js application to work with DynamoDB is fairly easy. First, make sure that aws-sdk is installed, either by running yarn add aws-sdk or npm i aws-sdk --save. Then, paste following piece of code:

As one of the Node.js best practices is to avoid callback hell, we'll be ending up all of our SDK calls with .promise() call in order to get Promises returned from SDK. It will also allow us to use async/await syntax which makes our programs much more readable.

Keep in mind that using access and secret keys is against best security practices, and you should instead use IAM roles/policies to interact with DynamoDB. This code, if ran on Lamba function or EC2 instance, will automatically use IAM Role attached to it.

Create table

DynamoDB structures data in tables, so if you want to save some data to DynamoDB, first you need to create a table. You can do that using AWS Console, AWS CLI or using AWS-SDK for Javascript, like this:

After this call resolves, it does not necessarily mean that table status is ACTIVE and it's is ready for read and write operations. Before start manipulating items in it, we should check if it's in ACTIVE state first:

Get All Items / Scan in DynamoDB

After our table is provisioned and it's in ACTIVE state, first thing that we probably would like to do is get all items in it aka use (DynamoDB Scan operation):

If you want to narrow your search results, use FilterExpressions combined with ExpressionAttributeNames object like so:

You can find full reference how to write FilterExpressions in this post by Alex Debrie

Get Item

If you know the exact Partition Key (and Sort Key if using composite key) of the item that you want to retrieve from the DynamoDB table, you can use get operation:

Batch Get Item

DocumentClient is also capable of running bunch of get operations in a single call to the DynamoDB service:

As you can see, the RequestItems objects can accept multiple table names and can fetch multiple items from multiple tables in a single call. Keep in mind that number of items retrieved using batchGet is limited to 100 items or 16MB of data.

Moreover, if you exceed table capacity, this call will return UnprocessedKeys attribute containing a map of keys which weren't fetched.

Put Item aka Write

put operation creates a new item, or replaces an old item with a new item if it's using the same key(s):

Query Set of Items

If your table has composite key (which is the best practice), in order to get a collection of items sharing the same Parition Key, use Query method. It also allows to use multiple operators for SortKey such as begins_with or mathematical ones like >, =, >= and so on.

Keep in mind that Query can return up to 1MB of data and you can also use FilterExpressions here to narrow the results on non-key attributes.

If you don't know how to construct your Query and its attributes, head to our DynamoDB Query Builder which will generate code for you. You can also use Query Code Generation feature inside Dynobase.

Query with Sorting

Unfortunately, DynamoDB offers only one way of sorting the results on the database side - using the sort key. If your table does not have one, your sorting capabilities are limited to sorting items in application code after fetching the results. However, if you need to sort DynamoDB results on sort key descending or ascending, you can use following syntax:

Query (and Scan) DynamoDB Pagination

Both Query and Scan operations returns results up to 1MB of items. If you need to fetch more records, you need to invoke a second call to fetch the next page of results. If LastEvaluatedKey is present in response object, this table has more items like requested and another call with ExclusiveStartKey should be sent to fetch more of them:

Update Item

DynamoDB update operation in Node.js consists of two main parts:

  • Part which item to update (Key), similar to get
  • Part what in the selected item should be updated (UpdateExpression and ExpressionAttributeValues)

Conditionally Update Item

Sometimes we want to update our record only if some condition is met, e.g. item is not soft-deleted (does not have deletedAt attribute set). To do that, use ConditionExpression which has similar syntax to the FilterExpression:

In this example the name attribute of the record with partition key id = 123 in table my-table will be only updated if this item does not have attribute deletedAt and its attribute company has value Apple.

Increment Item Attribute

Incrementing a Number value in DynamoDB item can be achieved in two ways:

  1. Get item, update the value in the application code and send a put request back to DDB overwriting item
  2. Using update operation

While it might be tempting to use first method because Update syntax is unfriendly, I strongly recommend using second one because of the fact it's much faster (requires only one request) and atomic:

In this example the score attribute of the record with partition key id = 123 in table my-table will incremented by one.

Delete Item

Removing single item from table is very similar to Get Item operation. The parameters of the call are actually exactly the same, the only difference is that we call delete instead of get:

Delete All Items

Unfortunately, there's no easy way to delete all items from DynamoDB just like in SQL-based databases by using DELETE FROM my-table;. To achieve the same result in DynamoDB, you need to query/scan to get all the items in a table using pagination until all items are scanned and then perform delete operation one-by-one on each record.

Luckily, truncating table is possible just with few clicks using Dynobase.

Run DynamoDB Local

If you need to use DynamoDB offline locally, you can use DynamoDB local distributed by AWS or DynamoDB from Localstack. Connecting to it is as easy as changing the endpoint parameter DynamoDB or DocumentClient constructor:

If you want to see your local tables and data in them, you can use Dynobase to query and modify items in offline tables.

Bonus!

If you're looking for Serverless Framework based CRUD project which uses other AWS Lambda and DynamoDB best practices with Node.js, you can find one on our Github.

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