Return only unique record when using includes

Gemfile.lock

@@ -95,6 +95,7 @@ GEM
 
 PLATFORMS
   x86_64-darwin-21
+  x86_64-darwin-22
   x86_64-linux
 
 DEPENDENCIES

lib/fast_page/active_record_methods.rb

@@ -11,7 +11,7 @@ def deferred_join_load
       @values[:limit] = limit_value + 1 if limit_value
       id_scope = dup
       id_scope = id_scope.except(:includes) unless references_eager_loaded_tables?
-      ids = id_scope.pluck(:id)
+      ids = id_scope.pluck(:id).uniq
 
       if limit_value
         @values[:limit] = limit_value - 1

test/fast_page_test.rb

@@ -7,11 +7,14 @@ def setup
     User.delete_all
     Organization.delete_all
 
-    org = Organization.create(name: "planetscale")
-    User.create(login: "mikeissocool", organization: org)
-    User.create(login: "iheanyi")
-    User.create(login: "nicknicknick")
-    User.create(login: "frances")
+    organizations = [
+      Organization.create(name: "planetscale"),
+      Organization.create(name: "github")
+    ]
+    User.create(login: "mikeissocool", organizations: [organizations[0], organizations[1]])
+    User.create(login: "iheanyi", organizations: [organizations[0], organizations[1]])
+    User.create(login: "nicknicknick", organizations: [organizations[0]])
+    User.create(login: "frances", organizations: [organizations[1]])
     User.create(login: "phani")
     User.create(login: "jason")
     User.create(login: "derek")
@@ -54,15 +57,16 @@ def test_removes_includes_id_query
       queries << sql.payload[:sql]
     end
 
-    User.all.includes(:organization).limit(50).fast_page
+    User.all.includes(:organizations).limit(50).fast_page
 
-    assert_equal 3, queries.size
+    assert_equal 4, queries.size
 
     # Organizations are not included on the ID query (not needed)
     assert_includes queries, 'SELECT "users"."id" FROM "users" LIMIT ?'
     assert_includes queries, 'SELECT "users".* FROM "users" WHERE "users"."id" IN (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)'
     # Includes are still loaded
-    assert_includes queries, 'SELECT "organizations".* FROM "organizations" WHERE "organizations"."id" = ?'
+    assert_includes queries, 'SELECT "user_organizations".* FROM "user_organizations" WHERE "user_organizations"."user_id" IN (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)'
+    assert_includes queries, 'SELECT "organizations".* FROM "organizations" WHERE "organizations"."id" IN (?, ?)'
 
     ActiveSupport::Notifications.unsubscribe("sql.active_record")
   end
@@ -99,4 +103,12 @@ def test_works_offset_only
   def test_to_a_returns_an_array
     assert_equal Array, User.all.limit(5).fast_page.to_a.class
   end
+
+  def test_returns_unique_records_when_including_associations
+    og = User.includes(:organizations).where(organizations: { id: Organization.pluck(:id) }).limit(2).order(created_at: :asc)
+    fast = User.includes(:organizations).where(organizations: { id: Organization.pluck(:id) }).limit(2).order(created_at: :asc).fast_page
+
+    assert_equal og.length, fast.length
+    assert_equal og.select(&:id), fast.select(&:id)
+  end
 end

test/test_helper.rb

@@ -16,11 +16,16 @@
 
   create_table :users, force: true do |t|
     t.string :login
-    t.integer :organization_id
     t.timestamps
     t.index ["login"], unique: true
   end
 
+  create_table :user_organizations, force: true do |t|
+    t.integer :user_id
+    t.integer :organization_id
+    t.timestamps
+  end
+
   create_table :organizations, force: true do |t|
     t.string :name
     t.timestamps
@@ -31,5 +36,5 @@ class Organization < ActiveRecord::Base
 end
 
 class User < ActiveRecord::Base
-  belongs_to :organization
+  has_and_belongs_to_many :organizations, join_table: "user_organizations"
 end