SQL » Joins

To load associated relations you can simply use join, left_join, or right_join.

Using joins with relations

class Users < ROM::Relation[:sql]
  schema(infer: true) do
    associations do
      has_many :tasks
      has_many :posts
    end
  end

  def with_tasks
    join(tasks)
  end

  def with_posts
    left_join(posts)
  end
end

Auto-qualifying

When you pass a relation as the argument for join methods, the resulting relation will have all attributes qualified automatically for you

Using joins with explicit name and options

If you want to have more control, you can pass table name and additional options yourself:

class Users < ROM::Relation[:sql]
  schema(infer: true) do
    associations do
      has_many :tasks
      has_many :posts
    end
  end

  def with_tasks
    join(:tasks, user_id: :id, priority: 1)
  end

  def with_posts
    left_join(:posts, user_id: :id)
  end
end

Using joins with additional options

The second option hash can be used too, if you want to provide more options:

class Users < ROM::Relation[:sql]
  schema(infer: true) do
    associations do
      has_many :tasks
      has_many :posts
    end
  end

  def with_tasks
    join(:tasks, { user_id: :id }, table_alias: :user_tasks)
  end

  def with_posts
    left_join(posts, { user_id: :id }, table_alias: :user_posts)
  end
end

Learn more

Check out API docs: