SequelMapper

Very new, much experimental, so incomplete

What it is

SequelMapper is a data mapper that pulls rows out of your database and maps them into a graph of plain Ruby objects. The graph can then be modifed and persisted back into the database as a whole.

The main feature is that it fully supports all the kinds of data associations that you are used to with ActiveRecord but for your POROs.

It is built on top of Jeremy Evans' Sequel library.

Why is it?

• It seems like ROM may not be finished any time soon and I felt I could put together something functional albeit less ambitious
• I love the Sequel library
• I love decoupling persistence
• Writing a complex datamapper is sure way to stall your project so I'm writing one for you
• I am a sick person who enjoys this sort of thing

So go on, persist those POROs, they don't even have to know about it.

Example

  # Let's say you have some domain objects

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

  # And a relational database with some tables that look similar

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

  user_mapper = SequelMapper::Graph.new(
    top_level_namespace: :users,
    datastore: DB,
    config: mapper_config, # Config omitted
  )

  # Then this may appeal to you

  user = user_mapper.where(id: 1).first
  # => [#<struct User
  #       id=1,
  #       first_name="Stephen",
  #       last_name="Best",
  #       email="bestie@gmail.com",
  #       posts=#<SequelMapper::AssociationProxy:0x007ffbc3c7cb50 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>>]

  user.posts
  # => #<SequelMapper::AssociationProxy:0x007ffbc3c7cb50 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>
  # That's lazily evaluated try ...

  user.posts.to_a
  # => [#<struct Post
  #       id=1,
  #       author=
  #        #<struct User
  #         id=1,
  #         first_name="Stephen",
  #         last_name="Best",
  #         email="bestie@gmail.com",
  #         posts=#<SequelMapper::AssociationProxy:0x007ffbc3c7cb50 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>>,
  #       subject="Object mapping",
  #       body="It is often tricky",
  #       comments=#<SequelMapper::AssociationProxy:0x007ffbc59377b8 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>,
  #       categories=#<SequelMapper::AssociationProxy:0x007ffbc5936138 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>>,
  #      #<struct Post
  #       id=2,
  #       author=
  #        #<struct User
  #         id=1,
  #         first_name="Stephen",
  #         last_name="Best",
  #         email="bestie@gmail.com",
  #         posts=#<SequelMapper::AssociationProxy:0x007ffbc3c7cb50 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>>,
  #       subject="Object mapping part 2",
  #       body="Lazy load all the things!",
  #       comments=#<SequelMapper::AssociationProxy:0x007ffbc5935990 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>,
  #       categories=#<SequelMapper::AssociationProxy:0x007ffbc592fe50 @assoc_enum=#<Enumerator::Lazy: ...>, @removed_nodes=[]>>]

  # And then access the comments and so on ...

Installation

Add this line to your application's Gemfile:

gem 'sequel_mapper'

And then execute:

$ bundle

Or install it yourself as:

$ gem install sequel_mapper