Awesome

Faraday

Amazon DynamoDB client for Clojure

API reference: Codox, clj-doc
Leiningen: [com.taoensso/faraday "1.12.3"]
deps.edn: com.taoensso/faraday {:mvn/version "1.12.3"}

DynamoDB makes a great companion for Clojure apps that need a simple, reliable way to persist data, that scales with predictable performance. Faraday is a small, fast and intuitive DynamoDB client library for Clojure, built around the AWS Java SDK and originally adapted from Rotary by James Reeves.

Why Faraday?

Small and simple API, with coverage of the most useful DynamoDB features
Great performance (zero overhead to the official Java SDK)
Uses Nippy for full support of Clojure's rich data types (with compression too)
The AWS Java SDK for DynamoDB is awkward and verbose
General purpose AWS SDKs for Clojure such as Amazonica or aws-api inherit the awkwardness of the AWS SDK when used to interact with DynamoDB

Getting started

Add Faraday as a dependency to your project and import faraday into your namespace:

(ns my-ns
 (:require [taoensso.faraday :as far]))

Preparing a database

Option 1 - Run a local DynamoDB instance

First thing is to start a DynamoDB Local instance. Once DynamoDB Local is up and running in your terminal, you should see something like:

$ docker run -p 8000:8000 amazon/dynamodb-local
Initializing DynamoDB Local with the following configuration:
Port:		8000
InMemory:	true
DbPath:		null
SharedDb:	false
shouldDelayTransientStatuses:	false
CorsParams:	*

Then proceed to connecting with your local instance in the next section.

Option 2 - Use DynamoDB in the cloud

Make sure you've got an AWS account - note that there's a free tier with limited DynamoDB storage and read/write throughput. Next you'll need credentials for an IAM user with read/write access to your DynamoDB tables.

Ready?

Connecting

(def client-opts
  {;;; For DynamoDB Local just use some random strings here, otherwise include your
   ;;; production IAM keys:
   :access-key "<AWS_DYNAMODB_ACCESS_KEY>"
   :secret-key "<AWS_DYNAMODB_SECRET_KEY>"

   ;;; You may optionally override the default endpoint if you'd like to use DynamoDB
   ;;; Local or a different AWS Region (Ref. http://goo.gl/YmV80o), etc.:
   ;; :endpoint "http://localhost:8000"                   ; For DynamoDB Local
   ;; :endpoint "http://dynamodb.eu-west-1.amazonaws.com" ; For EU West 1 AWS region

   ;;; You may optionally provide your own (pre-configured) instance of the Amazon
   ;;; DynamoDB client for Faraday functions to use.
   ;; :client (AmazonDynamoDBClientBuilder/defaultClient)
  })

(far/list-tables client-opts)
=> [] ; That's good, we don't have any tables yet :)

Now let's create a table. This is actually one of the more complicated parts of working with DynamoDB since it requires understanding how DynamoDB provisions capacity and how its idiosyncratic primary keys work. We can safely ignore the specifics for now.

(far/create-table client-opts :my-table
  [:id :n]  ; Primary key named "id", (:n => number type)
  {:throughput {:read 1 :write 1} ; Read & write capacity (units/sec)
   :block? true ; Block thread during table creation
   })

;; Wait a minute for the table to be created... got a sandwich handy?

(far/list-tables client-opts)
=> [:my-table] ; There's our new table!

Let's write something to :my-table and then fetch it:

(far/put-item client-opts
    :my-table
    {:id 0 ; Remember that this is our primary (indexed) key
     :name "Steve" :age 22 :data (far/freeze {:vector    [1 2 3]
                                              :set      #{1 2 3}
                                              :rational (/ 22 7)
                                              ;; ... Any Clojure data goodness
                                              })})

(far/get-item client-opts :my-table {:id 0})
=> {:id 0 :name "Steve" :age 22 :data {:vector [1 2 3] ...}}

Remaining API

DynamoDB gives you tons of power including secondary indexes, conditional writes, batch operations, atomic counters, tuneable read consistency and more.

Most of this stuff is controlled through optional arguments and is pretty easy to pick up by seeing the relevant [API] docs:

Tables: list-tables, describe-table, create-table, ensure-table, update-table, delete-table.

Items: get-item, put-item, update-item, delete-item.

Batch items: batch-get-item, batch-write-item.

Querying: query, scan, scan-parallel.

Transactions: transact-write-items, transact-get-items

You can also check out the official AWS DynamoDB documentation, though there's a lot of Java-land complexity that you won't need to deal with when using Faraday. The most useful single doc is probably on the DynamoDB data model and the DynamoDB Best Practices.

Development

This project uses Testcontainers to manage starting and stopping a local DynamoDB instance in docker.

Run the tests locally with:

lein test

Or run tests from a REPL like:

taoensso.faraday.tests.main> (clojure.test/run-tests)

To run the entire test suite against all supported versions of Clojure, use:

lein test-all

Contributions

Please see GitHub issues for bugs, ideas, etc. Pull requests welcome. For a general question on usage, try StackOverflow or ask the Faraday users and developers in #faraday at clojurians.slack.com.

License