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AWS DynamoDB & Rust - Complete Cheat Sheet

Chris Biscardi

Written by Chris Biscardi

Published on 2022-02-10

DynamoDB Rust Query Examples

This cheat sheet should help you understand how to perform a variety of operations starting from simple queries ending with complex transactions using the AWS Rust SDK.

The AWS Rust SDK doesn't currently have a high level DocumentClient like Node.js does, so you'll see more low-level DynamoDB concepts like defining types using AttributeValues when using the SDK.

Table of Contents

Setup

You'll want to include aws_config and aws_sdk_dynamodb in your Cargo.toml. Using cargo-edit:

Typically you'll load the region and other configuration from the environment using aws_config and then pass that to the dynamodb Client::new method to create a new dynamodb client.

The AWS Rust SDK takes advantage of async support with Tokio - an asynchronous runtime for Rust.


If you aren't comfortable with Rust, check out Rust Adventure by Chris Biscardi, an author of this blogpost where he teaches Rust the practical way by building Serverless Functions, interacting with Planetscale SQL databases, and even building a small game!


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, CDK, or using the aws-sdk-rust, like this:

The create_table call succeeding does not mean the database is ready to be used. Before we start manipulating items in it, we should check if it's in ACTIVE state first using the describe_table function ran every 5 seconds until it is ready:

Delete Table

If you changed your mind and need to remove DynamoDB table, don't worry, it's simple:

Keep in mind that Dynobase is capable of removing tables too.

List Tables

If you want to check what tables are available at your disposal in current region, use the list_tables call. Keep in mind that if selected region has more than 100 tables you'll have to paginate through them to fetch a complete list.

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.

The snippet above will in fact return all the items in the table under one condition - you have less than 1MB of data inside it. If your table is bigger than that, you'll have to run Scan command a few times in a loop using pagination.

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

aws-sdk-rust 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 batch_get_item 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_item operation creates a new item, or replaces an old item with a new item if it's using the same key(s):

Batch Write / Put Item

If you need to insert, update or delete multiple items in a single API call, use the batch_write_item operation. It bundles multiple database requests against multiple tables into a single SDK call. It decreases amount of network calls needed to be made, reduces the overall latency and makes your application faster.

Example request writing two different items.

If you are curious about performance of batch_write_item, head to dynamodb-performance-testing repo by Alex DeBrie.

Query for a 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.

Query an Index

DynamoDB allows querying not only on the main table index, but also on LSIs (Local Secondary Indexes) and GSIs (Global Secondary Indexes).

To do that in SDK, you need to change two things:

  • Specify the index you want to query using index_name parameter
  • Provide correct KeyConditionExpression with corresponding ExpressionAttributeValues and ExpressionAttributeNames So, to give you an example. Imagine your table is having a Global Secondary Index called GSI1 with attributes gsi1pk and gsi1sk. If you'd like to query that index in Rust, it will look like this:

Simple Transaction

DynamoDB also support transactions - they allow to run multiple write operations atomically meaning that either all of operations are executed succesfully or none of them. It is especially useful when dealing with applications where data integrity is essential, e.g. in e-commerce - adding an item to a cart and decrementing count of items still available to buy.

Such flow should:

Should happen atomically - these two operations should be treated as one, we don't want to have a single moment in time where there's a discrepancy in items count Should succeed only if count of items available to buy is greated than zero

Described flow can be modelled in Rust like this:

If you want to learn more about transactions, head to our DynamoDB Transactions Guide.

Read Transaction

Transactions can be also used for reading data atomically. Like in batch_get_item, you can retrieve the data from multiple tables in a single call:

If you want to learn more about transactions, head to our DynamoDB Transactions Guide.

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 return results with 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:

Learn more about Pagination in DynamoDB.

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 name = joe 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:

  • Get item, update the value in the application code and send a put request back to DDB overwriting item
  • 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:

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:


Uplevel Your Rust Skills

This article was brought to you by Chris Biscardi. Chris is an author of Rust Adventure, one of the best Rust courses you can get on the market right now.

In Rust Adventure, you will experience the versatility of the Rust language through building games, powerful CLI apps, and serverless functions. Whether your goal is to jumpstart the next stretch of your development career or just to tinker, Rust Adventure is what you need.

I highly recommend it! - Rafal from Dynobase


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