AWS Developer Blog

General Availability Release of the aws-record Gem

by Alex Wood | on | in Ruby | Permalink | Comments |  Share

Today, we’re pleased to announce the GA release of version 1.0.0 of the aws-record gem.

What Is aws-record?

In version 1 of the AWS SDK for Ruby, the AWS::Record class provided a data mapping abstraction over Amazon DynamoDB operations. Earlier this year, we released the aws-record developer preview as a separately packaged library to provide a similar data mapping abstraction for DynamoDB, built on top of the AWS SDK for Ruby version 2. After customer feedback and some more development work, we’re pleased to move the library out of developer preview to general availability.

How to Include the aws-record Gem in Your Project

The aws-record gem is available now from RubyGems:

 

gem install aws-record

 

You can also include it in your project’s Gemfile:

 

# Gemfile
gem 'aws-record', '~> 1.0'

 

This automatically includes a dependency on the aws-sdk-resources gem, major version 2. Be sure to include the aws-sdk or aws-sdk-resources gem in your Gemfile if you need to lock to a specific version, like so:

 

 # Gemfile
gem 'aws-record', '~> 1.0'
gem 'aws-sdk-resources', '~> 2.5'

 

Working with DynamoDB Tables Using the aws-record Gem

Defining an Aws::Record Model

The aws-record gem provides the Aws::Record module, which you can include in a class definition. This decorates your class with a variety of helper methods that can simplify interactions with Amazon DynamoDB. For example, the following model uses a variety of preset attribute definition helper methods and attribute options:

 

require 'aws-record'

class Forum
  include Aws::Record  

  string_attr     :forum_uuid, hash_key: true
  integer_attr    :post_id,    range_key: true
  string_attr     :author_username
  string_attr     :post_title
  string_attr     :post_body
  string_set_attr :tags,       default_value: Set.new 
  datetime_attr   :created_at, database_attribute_name: "PostCreatedAtTime"
  boolean_attr    :moderation, default_value: false
end

 

Using Validation Libraries with an Aws::Record Model

The aws-record gem does not come with a built-in validation process. Rather, it is designed to be a persistence layer, and to allow you to bring your own validation library. For example, the following model includes the popular ActiveModel::Validations module, and has defined a set of validations that will be run when we attempt to save an item:

 

require 'aws-record'
require 'active_model'

class Forum
  include Aws::Record
  include ActiveModel::Validations

  string_attr     :forum_uuid, hash_key: true
  integer_attr    :post_id,    range_key: true
  string_attr     :author_username
  string_attr     :post_title
  string_attr     :post_body
  string_set_attr :tags,       default_value: Set.new 
  datetime_attr   :created_at, database_attribute_name: "PostCreatedAtTime"
  boolean_attr    :moderation, default_value: false 


  validates_presence_of :forum_uuid, :post_id, :author_username
  validates_length_of :post_title, within: 4..30
  validates_length_of :post_body,  within: 2..5000
end

 

Creating a DynamoDB Table for a Model with Aws::Record::TableMigration

The aws-record gem provides a helper class for table operations, such as migrations. If we wanted to create a table for our Forum model in DynamoDB, we would run the following migration:

 

migration = Aws::Record::TableMigration.new(Forum)
migration.create!(
  provisioned_throughput: {
    read_capacity_units: 5,
    write_capacity_units: 2
  }
)
migration.wait_until_available

 

You can write these migrations in your Rakefile or as standalone helper scripts for your application. Because you don’t need to update your table definition for additions of non-key attributes, you may find that you’re not running migrations as often for your Aws::Record models.

Working with DynamoDB Items Using the aws-record Gem

Creating and Persisting a New Item

Using the example model above, once it has been created in the DynamoDB remote end using Aws::Record::TableMigration (or if it already existed in the remote end), it is simple to create and save a new item:

 

post = Forum.new(
  forum_uuid: FORUM_UUID,
  post_id: 1,
  author_username: "Author One",
  post_title: "Hello!",
  post_body: "Hello, world!"
)
post.created_at = Time.now
post.save # Performs a put_item call.

 

You can set attributes when you initialize a new item and with setter methods that are defined for you automatically.

Finding and Modifying an Item

A class-level method #find is provided to look up items from DynamoDB using your model’s key attributes. After setting a few new attribute values, calling #save will make an update call to DynamoDB, reflecting only the item changes you’ve made. This is important for users who are fetching items with projections (which may not include all attributes), or using single-table inheritance patterns (who may not have modeled all attributes present in a remote item), to avoid clobbering unmodeled or non-included attribute values.

 

post = Forum.find(forum_uuid: FORUM_UUID, post_id: 1)
post.post_title = "(Removed)"
post.post_body = "(Removed)"
post.moderation = true
post.save # Performs an update_item call on dirty attributes only.

 

There is also a class-level method to directly build and make an update call to DynamoDB, using key attributes to identify the item and non-key attributes to form the update expression:

 

Forum.update(
  forum_uuid: FORUM_UUID,
  post_id: 1,
  post_title: "(Removed)",
  post_body: "(Removed)",
  moderation: true
)

 

The preceding two code examples are functionally equivalent. You’ll have the same database state after running either snippet.

A Note on Dirty Tracking

In our last example, we talked about how item updates only reflect changes to modified attributes. Users of ActiveRecord or similar libraries will be familiar with the concept of tracking dirty attribute values, but aws-record is a bit different. That is because DynamoDB supports collection attribute types, and in Ruby, collection types are often modified through object mutation. To properly track changes to an item when objects can be changed through mutable state, Aws::Record items will, by default, keep deep copies of your attribute values when loading from DynamoDB. Attribute changes through mutation, like this example, will work the way you expect:

 

post = Forum.find(forum_uuid: FORUM_UUID, post_id: 1)
post.tags.add("First")
post.dirty? # => true
post.save # Will call update_item with the new tags collection.

 

Tracking deep copies of attribute values has implications for performance and memory. You can turn off mutation tracking at the model level. If you do so, dirty tracking will still work for new object references, but will not work for mutated objects:

 

class NoMTModel
  include Aws::Record
  disable_mutation_tracking
  string_attr :key, hash_key: true
  string_attr :body
  map_attr    :map
end

item = NoMTModel.new(key: "key", body: "body", map: {})
item.save # Will call put_item
item.map[:key] = "value"
item.dirty? # => false, because we won't track mutations to objects
item.body = "New Body"
item.dirty? # => true, because we will still notice reassignment
# Will call update_item, but only update :body unless we mark map as dirty explicitly.
item.save

 

Try the aws-record Gem Today!

We’re excited to hear about what you’re building with aws-record. Feel free to leave your feedback in the comments, or open an issue in our GitHub repo. Read through the documentation and get started!