update foreword/preface example

Author: ezekg

README.md

@@ -54,25 +54,30 @@ class Book < ActiveRecord::Base
   has_many :coauthorships
   has_many :coauthors, through: :coauthorships, source: :user
 
-  # editors for the book via a join table
-  has_many :edits
-  has_many :editors, through: :edits, source: :user
+  # prefacers for the book via a join table
+  has_many :forewords
+  has_many :foreworders, through: :forewords, source: :user
+
+  # prefacers for the book via a join table
+  has_many :prefaces
+  has_many :prefacers, through: :prefaces, source: :user
 
   # illustrators for the book via a join table
   has_many :illustrations
   has_many :illustrators, through: :illustrations, source: :user
 
-  # foreword writers for the book via a join table
-  has_many :forewords
-  has_many :prefacers, through: :forewords, source: :user
+  # editors for the book via a join table
+  has_many :edits
+  has_many :editors, through: :edits, source: :user
 
   # union association for all contributors to the book
-  has_many :contributors, class_name: 'User', union_of: %i[
+  has_many :contributors, -> { distinct }, class_name: 'User', union_of: %i[
     author
     coauthors
-    editors
-    illustrators
+    foreworders
     prefacers
+    illustrators
+    editors
   ]
 end
 ```
@@ -95,9 +100,12 @@ Edit.create(user: editor, book:)
 # assign an illustrator
 Illustration.create(user: illustrator, book:)
 
-# assign a foreword writer
+# assign a foreword by the author
 Foreword.create(user: writer, book:)
 
+# assign a preface writer
+Preface.create(user: author, book:)
+
 # access all contributors (author, editor, illustrator, etc.)
 book.contributors.to_a
 # => [#<User id=1, name="Isaac Asimov">, #<User id=2, name="John W. Campbell">, #<User id=3, name="Frank Kelly Freas">, #<User id=4, name="Ray Bradbury">]

spec/union_of_spec.rb

@@ -1340,6 +1340,11 @@ def owned = where(owner: proxy_association.owner)
       t.integer :user_id
     end
 
+    temporary_table :prefaces do |t|
+      t.integer :book_id
+      t.integer :user_id
+    end
+
     temporary_model :user do
       has_many :books
       has_many :coauthorships
@@ -1368,33 +1373,36 @@ def owned = where(owner: proxy_association.owner)
       belongs_to :user
     end
 
+    temporary_model :preface do
+      belongs_to :book
+      belongs_to :user
+    end
+
     temporary_model :book do
-      # the primary author of the book
       belongs_to :author, class_name: 'User', foreign_key: 'author_id', optional: true
 
-      # coauthors of the book via a join table
       has_many :coauthorships
       has_many :coauthors, through: :coauthorships, source: :user
 
-      # editors for the book via a join table
-      has_many :edits
-      has_many :editors, through: :edits, source: :user
+      has_many :forewords
+      has_many :foreworders, through: :forewords, source: :user
+
+      has_many :prefaces
+      has_many :prefacers, through: :prefaces, source: :user
 
-      # illustrators for the book via a join table
       has_many :illustrations
       has_many :illustrators, through: :illustrations, source: :user
 
-      # foreword writers for the book via a join table
-      has_many :forewords
-      has_many :prefacers, through: :forewords, source: :user
+      has_many :edits
+      has_many :editors, through: :edits, source: :user
 
-      # union association for all contributors to the book
-      has_many :contributors, class_name: 'User', union_of: %i[
+      has_many :contributors, -> { distinct }, class_name: 'User', union_of: %i[
         author
         coauthors
-        editors
-        illustrators
+        foreworders
         prefacers
+        illustrators
+        editors
       ]
     end
 
@@ -1405,9 +1413,10 @@ def owned = where(owner: proxy_association.owner)
     let(:book) {
       book = Book.create(title: 'I, Robot', author:)
 
-      Edit.create(user: editor, book:)
+      Foreword.create(user: author, book:)
+      Preface.create(user: writer, book:)
       Illustration.create(user: illustrator, book:)
-      Foreword.create(user: writer, book:)
+      Edit.create(user: editor, book:)
 
       book
     }
@@ -1427,7 +1436,7 @@ def owned = where(owner: proxy_association.owner)
     it 'should use UNION' do
       expect(book.contributors.to_sql).to match_sql <<~SQL.squish
         SELECT
-          users.*
+          DISTINCT users.*
         FROM
           users
         WHERE
@@ -1460,9 +1469,18 @@ def owned = where(owner: proxy_association.owner)
                   SELECT
                     users.id
                   FROM
-                    users INNER JOIN edits ON users.id = edits.user_id
+                    users INNER JOIN forewords ON users.id = forewords.user_id
                   WHERE
-                    edits.book_id = 1
+                    forewords.book_id = 1
+                )
+                UNION
+                (
+                  SELECT
+                    users.id
+                  FROM
+                    users INNER JOIN prefaces ON users.id = prefaces.user_id
+                  WHERE
+                    prefaces.book_id = 1
                 )
                 UNION
                 (
@@ -1478,9 +1496,9 @@ def owned = where(owner: proxy_association.owner)
                   SELECT
                     users.id
                   FROM
-                    users INNER JOIN forewords ON users.id = forewords.user_id
+                    users INNER JOIN edits ON users.id = edits.user_id
                   WHERE
-                    forewords.book_id = 1
+                    edits.book_id = 1
                 )
               ) users
           )