schema-assoc-preview.rb

class Users < ROM::Relation[:users]
  schema do
    attribute :id, Types::Serial
    attribute :name, Types::String
    
    associate do
      many :posts
    end
  end
end

class Posts < ROM::Relation[:posts]
  schema do
    attribute :id, Types::Serial
    attribute :user_id, Types::ForeignKey(:users)
    attribute :title, Types::String
    attribute :body, Types::String
    
    associate do
      many :tags, through: :posts_tags
    end
  end
end

class UserRepo < ROM::Repository[:users]
end

class PostRepo < ROM::Repository[:posts]
end

user_repo = UserRepo.new(rom_container)
post_repo = PostRepo.new(rom_container)

user_repo.aggregate(:posts) # returns users with their posts
post_repo.aggregate(:tags) # returns posts with their tags