SequelCombine

This extension adds the Sequel::Dataset#combine method, which returns object from database composed with childrens, parents or any object where exists any relationship. Now it is possible in one query!

Installation

Add this line to your application's Gemfile:

gem 'sequel-combine'

And then execute:

$ bundle

Or install it yourself as:

$ gem install sequel-combine

The plugin needs to be initialized by the Sequel extension interface. The simplest way to configure plugin globally is adding this line to the initializer:

Sequel.extension :combine

or

Sequel::Database.extension :combine

But anyway I recommend reading more about Sequel extensions system.

Usage

Remember! Combined dataset it's still a dataset so methods can be chained!

Combining works only with Postgres adapter

dataset_first
  .combine(many: { attribute: [dataset_second, p_key_dataset_second: :f_key_dataset_first] })
  .to_a

• dataset_first, dataset_second -> datasets which needs to be combined
• many -> method used in combining. If relation is one-to-one recommended method is one(which return object or nil), in any other case I recommend to using method many(which return array of objects or empty array).
• attribute -> attribute which will be an result of combine
• p_key_dataset_second: :f_key_dataset_first -> relationship between tables

Usage examples

Combining many

DB[:groups].columns
  #=> [:id, :name]
DB[:users].columns
  #=> [:id, :username, :email, :group_id]
DB[:groups].combine(many: { users: [DB[:users], id: :group_id] }).to_a
  #=> [{:id=>1,
  #     :name=>"Football",
  #     :users=>
  #       [{
  #           :id=> 1,
  #           :username=> "leonardo",
  #           :email=> "[email protected]",
  #           :group_id=> 1,
  #         },
  #         {
  #           :id=> 2,
  #           :username=> "leonardo2",
  #           :email=> "[email protected]",
  #           :group_id=> 1,
  #         },
  #       ]
  #   }]

Combining one

DB[:groups].columns
  #=> [:id, :name]
DB[:users].columns
  #=> [:id, :username, :email, :group_id]
DB[:users].combine(one: { group: [DB[:groups], group_id: :id] }).to_a
  #=> [
  #     {
  #       :id=> 1,
  #       :username=> "leonardo",
  #       :email=>  "[email protected]",
  #       :group=> { :id=> 1, :name=> "Football" },
  #     },
  #     {
  #       :id=> 2,
  #       :username=> "leonardo2",
  #       :email=> "[email protected]"
  #       :group=> { :id=> 1, :name=> "Football" },
  #     }
  #   ]

Combining one and many

Also combining can be mixed and multiplied:

DB[:users].combine(
    one: {
      group: [DB[:groups], group_id: :id],
      company: [DB[:companies], company_id: :id],
    },
    many: {
      tasks: [DB[:tasks], id: :user_id],
      roles: [DB[:roles], id: :user_id],
    },
  ).to_a

Combining inside combine

It can go deeper and deeper...

DB[:projects].combine(
  many: {
    users: [
      DB[:users].combine(one: { city: [DB[:cities], city_id: :id] }),
      id: :project_id,
    ]
  }
).to_a

Self-combining and combining not by foreign_key

DB[:geolocations].combine(one: { parent: [DB[:geolocations], path: :parent_path] }).to_a

Combining more complex datasets

Datasets used in combine might be of course chained with other Sequel::Dataset methods.

DB[:groups]
    .where(id: 1)
    .select(:id, :name)
    .order(:name)
    .combine(
        many: {
            users: [
                DB[:users]
                    .join(:groups)
                    .select(:id, :username, :group_id, Sequel.qualify("groups", "name")),
                id: :group_id
            ]
        }
    ).to_a

Benchmark

Tested on 2000 mocked records with children's or parents:

4 level of combine - 2,39 sec.

3 level - 1,12 sec.

2 level - 0,55 sec.

1 level - 0,22 sec.

self-combining (the situation from geolocation, tested on real geolocations database, around 23000 records) - 4 sec

Use cases

• API directly in Postgresql
• Exporting tree of objects
• deep clone in Postgresql - very extreme case, but it's probably the most performance effective way of doing this operation
• more, more, more...

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request