Reading aggregate

book.rb

class Book < Hanami::Entity
  attributes do
    attribute :id, Types::Int
    attribute :title, Types::String
    attribute :author, Types::String
    attribute :publisher, Types::String
  end
end

book_repository.rb

class BookRepository < Hanami::Repository
  
  def all_with_author_and_publisher
   books.read query_with_author_and_publisher
  end
  
  private
  
  def query_with_author_and_publisher
    <<-SQL
      SELECT b.id, b.name title, a.name author, p.name publisher
      FROM books AS b
      JOIN authors AS a ON a.id = b.author_id
      JOIN publishers AS p ON p.id = b.publisher_id;
    SQL
  end
end

books.sql

CREATE TABLE publishers(
id serial primary key,
name text);

CREATE TABLE authors(
id serial primary key,
name text);

CREATE TABLE books(
id serial primary key,
author_id int references authors(id),
publisher_id int references publishers(id),
name text);

INSERT INTO authors (name) VALUES ('Douglas Adams');
INSERT INTO authors (name) VALUES ('William Gibson');
INSERT INTO publishers (name) VALUES ('Victor Gollancz Ltd');
INSERT INTO publishers (name) VALUES ('GPPutnam Sons');
INSERT INTO publishers (name) VALUES ('Pan Books');
INSERT INTO books (author_id, publisher_id, name) VALUES (1,3,'The Meaning of Liff ');
INSERT INTO books (author_id, publisher_id, name) VALUES (2,1,'Mona Lisa Overdrive');
INSERT INTO books (author_id, publisher_id, name) VALUES (2,2,'Pattern Recognition');

SELECT b.id, b.name title, a.name author, p.name publisher
FROM books AS b
JOIN authors AS a ON a.id = b.author_id
JOIN publishers AS p ON p.id = b.publisher_id;