SequelMapper

TL;DR

A Ruby ORM that enables DDD and clean architectural styles.
Persists plain objects while supporting arbitrarily deeply nested / circular associations
Provides excellent database and query building support courtesy of Sequel library

SequelMapper (working title) is a new, currently experimental data mapper ORM implementation for Ruby.

The aim is to provide a convenient way to query and persist graphs of Ruby objects (think models with associations), while keeping those object completely isolated and decoupled from the database.

In contrast to Ruby's many active record implementations, domain objects require no special inherited or mixed in behavior in order to be persisted.

Features

Associations (belongs_to, has_many, has_many_through)
Automatic 'convention over configuration' that is fully customizable
Lazy loading for database read efficiency
Dirty tracking for database write efficiency
Predefined queries, scopes or subsets
Eager loading to avoid the n + 1 query problem

There are some conspicuous missing features that you may want to read more about. If you want to contribute to solving any of the problems listed please open an issue to discuss.

SequelMapper does not reinvent the wheel with querying abstraction and migrations, instead these responsibilities are delegated to Sequel such that its full power can be utilised.

For querying, migrations and creating your database connection see the Sequel documentation.

Getting started

Please try this out, experiment, open issues and pull requests. Please read the code of conduct first.

  # 1. Define some domain objects, structs will surfice for the example

  User = Struct.new(:id, :first_name, :last_name, :email, :posts)
  Post = Struct.new(:id, :author, :subject, :body, :created_at, :categories)
  Category = Struct.new(:id, :name, :posts)

  ## Also assume that a conventional database schema (think Rails) is in place,
  ## a column for each of the struct's attributes will be present. The posts
  ## table will have `author_id` as a foreign key to the users table. There is
  ## a join table named `categories_to_posts` which facilitates the many to
  ## many relationship.

  # 2. Configure a Sequel database connection

  ## Sequel Mapper does not manage your connection for you.
  ## Example assumes Postgres however Sequel supports many other databases.

  DB = Sequel.postgres(
    host: ENV.fetch("PGHOST"),
    user: ENV.fetch("PGUSER"),
    database: ENV.fetch("PGDATABASE"),
  )

  # 3. Configure mappings and associations

  ## This is kept separate from your domain models as knowledge of the schema
  ## is required to wire them up.

  USER_MAPPER_CONFIG = SequelMapper.config(DB)
    .setup_mapping(:users) { |users|
      users.has_many(:posts, foreign_key: :author_id)
    }
    .setup_mapping(:posts) { |posts|
      posts.belongs_to(:author, mapping_name: :users)
      posts.has_many_through(:categories)
    }
    .setup_mapping(:categories) { |categories|
      categories.has_many_through(:posts)
    }

  # 4. Create a mapper by combining a connection and a configuration

  USER_MAPPER = SequelMapper.mapper(
    datastore: DB,
    config: USER_MAPPER_CONFIG,
    name: :users,
  )

  ## You are not limted to one mapper configuration or one database connection.
  ## To handle complex situations you may create several segregated mappings
  ## for your separate aggregate roots, potentially utilising multiple
  ## databases and different domain object classes/compositions.

  # 5. Create some objects

  user = User.new(
    "2f0f791c-47cf-4a00-8676-e582075bcd65",
    "Hansel",
    "Trickett",
    "hansel@tricketts.org",
    [],
  )

  user.posts << Post.new(
    "9b75fe2b-d694-4b90-9137-6201d426dda2",
    user,
    "Things that I like",
    "I like fish and scratching",
    Time.parse("2015-10-03 21:00:00 UTC"),
    [],
  )

  # 6. Save them

  USER_MAPPER.save(user)

  ## Only the (aggregate) root object needs to be passed to the mapper.

  # 7. Query

  user = USER_MAPPER.where(id: "2f0f791c-47cf-4a00-8676-e582075bcd65").first

  # => #<struct User
  #  id="2f0f791c-47cf-4a00-8676-e582075bcd65",
  #  first_name="Stephen",
  #  last_name="Best",
  #  email="bestie@gmail.com",
  #  posts=#<SequelMapper::CollectionMutabilityProxy:7ff57192d510 >,

Running the tests

Set the following environment variables

PGHOST
PGUSER
PGDATABASE

Create a test database

This will create a database named from the value of PGDATABASE

$ bundle exec rake db:create

Run all tests (RSpec and Cucumber)

$ bundle exec rake

Should anything go awry

Drop the test database and start fresh

$ bundle exec rake db:drop

Installation

This library is still pre 1.0 so please lock down your version and update with care.

Add the following to your Gemfile.

gem "sequel_mapper", "0.0.3"

And then execute:

$ bundle

Or install it manually:

$ gem install sequel_mapper

lee-jon / sequel_mapper