Relation `join` method only returns columns of the relation running the `join`.

[calopez]

VERSIONS

• rom-sql (2.4.0)
• rom (4.2.1)

class User < ROM::Relation[:sql]
  schema(:users, infer: true) do
    associations do has_one :address end
  end
end

class Address < ROM::Relation[:sql]
  schema(:addresses, infer: true) do
    associations do belongs_to :user end
  end
end

ROM_ENV = ROM.container(:sql, 'sqlite::memory') do |config|
  gateway = config.gateways[:default]
  migration = gateway.migration do
    change do
      create_table :users do
        primary_key :id
        string :name, null: false
      end

      create_table :addresses do
        primary_key :id
        string :address_line_1, null: false
        foreign_key :user_id, :users
      end
    end
  end

  migration.apply(gateway.connection, :up)
  config.register_relation User
  config.register_relation Address
end

ROM::Relations Whe joining two relations only the columns of the relation running the join are returned. If I use assoc instead of join, only the columns of the joining relation are returned. If I use Sequel al columns are returned, which is the result I expect.

Reproducing the issue:

address = rom.relations[:addresses]
user = rom.relations[:users]

user.transaction do
   u = user.changeset(:create, name: 'carlos').commit  
   a = address.changeset(:create, address_line_1: 'Maxella 89 Av').associate(u, :users).commit   
end  
=> {:id=>1, :address_line_1=>"Maxella 89 Av", :user_id=>1}

user.join(:addresses).to_a
=> [{:id=>1, :name=>"carlos"}]

user.assoc(:addresses).to_a
=> [{:id=>1, :address_line_1=>"Maxella 89 Av", :user_id=>1}]

DB = rom.gateways[:default]
DB[:users].join(:addresses, { user_id: :id }).all
=> [{:id=>1, :name=>"carlos", :address_line_1=>"Maxella 89 Av", :user_id=>1}]

[solnic]

This is intended behavior. We use Sequel but it's an implementation detail, you should not have any expectations based on what Sequel does. The reason why we don't auto-append columns from a joined relation is pretty simple - you may have conflicting column names, and on top of that, auto-appending columns would be implicit behavior, we're trying to avoid that in rom in general.