OceanDynamo is a massively scalable Amazon DynamoDB near drop-in replacement for ActiveRecord.

OceanDynamo requires Ruby 2.0 and Ruby on Rails 4.0.0 or later. Rails 5.0.x is supported, but 5.1 will require a couple of changes.

src="https://badge.fury.io/rb/ocean-dynamo.png" alt="Gem Version" />[http://badge.fury.io/rb/ocean-dynamo]


As one important use case for OceanDynamo is to facilitate the conversion of SQL databases to no-SQL DynamoDB databases, it is important that the syntax and semantics of OceanDynamo are as close as possible to those of ActiveRecord. This includes callbacks, exceptions and method chaining semantics. OceanDynamo follows this pattern closely and is of course based on ActiveModel.

The attribute and persistence layer of OceanDynamo is modeled on that of ActiveRecord: there's save, save!, create, update, update!, update_attributes, find_each, destroy_all, delete_all, read_attribute, write_attribute and all the other methods you're used to. The design goal is always to implement as much of the ActiveRecord interface as possible, without compromising scalability. This makes the task of switching from SQL to no-SQL much easier.

OceanDynamo uses only primary indices to retrieve related table items and collections, which means it will scale without limits.

OceanDynamo is fully usable as an ActiveModel and can be used by Rails controllers. Thanks to its structural similarity to ActiveRecord, OceanDynamo works with FactoryBot.

OceanDynamo supports optimistic record locking via a combination of DynamoDB conditional writes and atomic updates. This is activated by default.

Current State

  • Secondary indices are now fully supported! See below for more information.
  • Version 2 of the AWS Ruby SDK is now used.
  • Work begun on association proxies, etc.

Future milestones

  • Direct support for the DynamoDB JSON attribute types for arrays and hashes
  • Collection proxies, to implement ActiveRecord-style method chaining, e.g.: blog_entry.comments.build(body: "Cool!").save!
  • The has_and_belongs_to_many assocation.

Current use

OceanDynamo is used as a central component in Ocean, a Rails framework and development, testing, and production pipeline for creating massively scalable HATEOAS microservice SOAs in the cloud.

However, OceanDynamo can of course also be used stand-alone.



Contributions are welcome. Fork in the usual way. OceanDynamo is developed using TDD: the specs are extensive and test coverage is very near to 100 percent. Pull requests will not be considered unless all tests pass and coverage is equally high or higher. All contributed code must therefore also be exhaustively tested.


Basic syntax

The following example shows the basic syntax for declaring a DynamoDB-based schema.

  class AsyncJob < OceanDynamo::Table

    dynamo_schema(:guid) do
      attribute :credentials,          :string
      attribute :token,                :string,     default: Proc { SecureRandom.uuid }
      attribute :steps,                :serialized, default: []
      attribute :max_seconds_in_queue, :integer,    default: 1.day
      attribute :default_poison_limit, :integer,    default: 5
      attribute :default_step_time,    :integer,    default: 30
      attribute :started_at,           :datetime
      attribute :last_completed_step,  :integer
      attribute :finished_at,          :datetime
      attribute :destroy_at,           :datetime,   local_secondary_index: true
      attribute :created_by
      attribute :updated_by
      attribute :succeeded,            :boolean,    default: false
      attribute :failed,               :boolean,    default: false
      attribute :poison,               :boolean,    default: false

      global_secondary_index :token, projection: :all



Each attribute has a name, a type (:string, :integer, :float, :datetime, :boolean, or :serialized) where :string is the default. Each attribute also optionally has a default value, which can be a Proc. The hash key attribute is by default :id (overridden as :guid in the example above) and is a :string.

The :string, :integer, :float and :datetime types can also store sets of their type. Sets are represented as arrays, may not contain duplicates and may not be empty.

All attributes except the :string type can take the value nil. Storing nil for a string value will return the empty string, "".

Schema args and options

dynamo_schema takes args and many options. Here's the full syntax:

   table_hash_key = :id,                   # The name of the hash key attribute
   table_range_key = nil,                  # The name of the range key attribute (or nil)
   table_name: compute_table_name,         # The basename of the DynamoDB table
   table_name_prefix: nil,                 # A basename prefix string or nil
   table_name_suffix: nil,                 # A basename suffix string or nil
   read_capacity_units: 10,                # Used only when creating a table
   write_capacity_units: 5,                # Used only when creating a table
   connect: :late,                         # true, :late, nil/false
   create: false,                          # If true, create the table if nonexistent
   locking: :lock_version,                 # The name of the lock attribute or nil/false
   timestamps: [:created_at, :updated_at], # A two-element array of timestamp columns, or nil/false
   client: nil,                            # A DynamoDB client or nil
) do
   # Attribute definitions

Tip: you might want to use the following idiom when declaring a dynamo_schema. It is used everywhere in Ocean:

 dynamo_schema(:id, table_name_suffix: Api.basename_suffix, create: true) do

This will auto-create the DynamoDB table in all environments and also add a suffix to the table name in order to prevent collisions during tests. Cf Api.basename_suffix in the ocean-rails gem for more information.

has_many and belongs_to


The following example shows how to set up has_many / belongs_to relations:

 class Forum < OceanDynamo::Table
   dynamo_schema do
     attribute :name
     attribute :description
   has_many :topics, dependent: :destroy

 class Topic < OceanDynamo::Table
   dynamo_schema(:guid) do
     attribute :title
   belongs_to :forum
   has_many :posts, dependent: :destroy

 class Post < OceanDynamo::Table
   dynamo_schema(:guid) do
     attribute :body
   belongs_to :topic, composite_key: true

The only non-standard aspect of the above is composite_key: true, which is required as the Topic class itself has a belongs_to relation and thus has a composite key. This must be declared in the child class as it needs to know how to retrieve its parent.


Restrictions for belongs_to tables:

  • The hash key must be specified and must not be :id.
  • The range key must not be specified at all.
  • belongs_to can be specified only once in each class.
  • belongs_to must be placed after the dynamo_schema attribute block.

Restrictions for has_many tables:

  • has_many must be placed after the dynamo_schema attribute block.

These restrictions allow OceanDynamo to implement the has_many / belongs_to relation in a very efficient and massively scalable way.


belongs_to claims the range key and uses it to store its own id, which normally would be stored in the hash key attribute. Instead, the hash key attribute holds the id of the parent. We have thus reversed the roles of these two fields. As a result, all children store their parent id in the hash key, and their own id in the range key.

This type of relation is even more efficient than its ActiveRecord counterpart as it uses only primary indices in both directions of the has_many / belongs_to association. No scans.

Furthermore, since DynamoDB has powerful primary index searches involving substrings and matching, the fact that the range key is a string can be used to implement wildcard matching of additional attributes. This gives, amongst other things, the equivalent of an SQL GROUP BY request, again without requiring any secondary indices.

It's our goal to use a similar technique to implement has_and_belongs_to_many relations, which means that secondary indices won't be necessary for the vast majority of DynamoDB tables. This ultimately means reduced operational costs, as well as reduced complexity.

Secondary Indices

Local Secondary Indices

Up to five attributes can be declared as local secondary indices, in the following manner:

  class Authentication < OceanDynamo::Table
    dynamo_schema(:username, :expires_at) do
      attribute :token,       :string,   local_secondary_index: true
      attribute :max_age,     :integer
      attribute :created_at,  :datetime
      attribute :expires_at,  :datetime
      attribute :api_user_id, :string

The items of the above table can be accessed by using the hash key :username and the range key :expires_at. The local_secondary_index declaration makes it possible to access items using the same hash key :username but with :token as an alternate range key. Local secondary indices all use the same hash key as the primary index, substituting another attribute instead as the range key.

NB: The primary index [:username, :expires_at] requires all items to have a unique combination of keys. Secondary indices don't require the range key to be unique for the same hash key. This means that secondary index searches always will return a collection.

Local secondary indices are queried through find_local_each and find_local. They take the same arguments; the former yields to a block for each item, the other returns all items in an array.

The following finds all Authentications where :username is "joe" and :token is "quux":

 Authentication.find_local(:username, "joe", :token, "=", "quux")

This retrieves all Authentications belonging to Joe, sorted on :token:

 Authentication.find_local(:username, "joe", :token, ">=", "0")

The same thing but with the only the item with the highest token value:

 Authentication.find_local(:username, "joe", :token, ">=", "0",
                           scan_index_forward: false, limit: 1)

Global Secondary Indices

Global secondary indices are declared after all attributes, but still within the do block:

  class Authentication < OceanDynamo::Table
    dynamo_schema(:username, :expires_at) do
      attribute :token,       :string,   local_secondary_index: true
      attribute :max_age,     :integer
      attribute :created_at,  :datetime
      attribute :expires_at,  :datetime
      attribute :api_user_id, :string

      global_secondary_index :token, projection: :all
      global_secondary_index :api_user_id, :expires_at, read_capacity_units: 100
      global_secondary_index :expires_at, write_capacity_units: 50

Each global_secondary_index clause (there can be a maximum of 5 per table) takes the following arguments:

  • hash_value (required),
  • range_value (optional),
  • :projection (default :keys_only, :all for all attributes)
  • :read_capacity_units (defaults to the table's read capacity, normally 10)
  • :write_capacity_units (default to the table's write capacity, normally 5)

Global secondary indices are queried through find_global_each and find_global. They take the same arguments; the former yields to a block for each item, the other returns all items in an array.

The following finds all Authentications whose :token is "quux":

 Authentication.find_global(:token, "quux")

This retrieves all Authentications belonging to the user with the ID "dfstw-ruyhdf-ewijf", sorted in ascending order of the :expires_at attribute:

 Authentication.find_global(:api_user_id, "dfstw-ruyhdf-ewijf",
                            :expires_at, ">=", 0)

To get the highest :expires_at record:

 Authentication.find_global(:api_user_id, "dfstw-ruyhdf-ewijf",
                            :expires_at, ">=", 0,
                            scan_index_forward: false, limit: 1)


gem install ocean-dynamo

Ocean-dynamo relies on Aws.config to fetch configuration data. In Ocean, we use an init file similar to this one:

cfg = if ENV['AWS_ACCESS_KEY_ID'].present? && ENV['AWS_SECRET_ACCESS_KEY'].present?
    region: ENV['AWS_REGION'],
    credentials: Aws::Credentials.new(ENV['AWS_ACCESS_KEY_ID'],
    region: "eu-west-1",    # Doesn't matter in this context
    credentials: Aws::Credentials.new('not', 'used'),
    region: ENV['AWS_REGION'],
    credentials: Aws::InstanceProfileCredentials.new

As you can see, this relies on ENV variables to choose from three different setups:

  1. If you're using discrete AWS credentials (not recommended), set AWS_REGION, AWS_ACCESS_KEY_ID, and AWS_SECRET_ACCESS_KEY.
  2. If you're using localstack, provide AWS_DYNAMODB_ENDPOINT (http://localhost:4569).
  3. If you're using EC2 or ECS instance profile credentials, set only AWS_REGION.

You can also supply a DynamoDB client for each table by using the keyword +client:+. If +nil+, the default config in +Aws.config+ will be used.

Running the specs

We're using localstack (https://github.com/localstack/localstack) for development and testing. Install (we use a Docker container) and run it. If you're using ocean-dynamo with the Ocean Rails context, you can install and start it by following the instructions in the ocean repo.

With localstack running, you should now be able to do

 bundle exec rspec

All tests should pass.

Rails console

The Rails console is available from the built-in dummy application:

 cd spec/dummy
 rails console

This will, amongst other things, also create the CloudModel table if it doesn't already exist. On Amazon, this will take a little while. With DynamoDB Local, it's practically instant.

When you leave the console, you must navigate back to the top directory (cd ../..) in order to be able to run RSpec again.