Merge pull request #23583 from brchristian/penultimate

Array.second_to_last and Array.third_to_last access methods

10 files changed, 86 insertions, 2 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index a4cf6023e1..be96f9fa2a 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add ActiveRecord `#second_to_last` and `#third_to_last` methods.
+
+    *Brian Christian*
+
 *   Added `numeric` helper into migrations.
 
     Example:
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 9f2c7292ea..2dca6b612e 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -136,6 +136,14 @@ module ActiveRecord
         first_nth_or_last(:forty_two, *args)
       end
 
+      def third_to_last(*args)
+        first_nth_or_last(:third_to_last, *args)
+      end
+
+      def second_to_last(*args)
+        first_nth_or_last(:second_to_last, *args)
+      end
+
       def last(*args)
         first_nth_or_last(:last, *args)
       end
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index fe693cfbb6..2a9627a474 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -197,6 +197,16 @@ module ActiveRecord
         @association.forty_two(*args)
       end
 
+      # Same as #first except returns only the third-to-last record.
+      def third_to_last(*args)
+        @association.third_to_last(*args)
+      end
+
+      # Same as #first except returns only the second-to-last record.
+      def second_to_last(*args)
+        @association.second_to_last(*args)
+      end
+
       # Returns the last record, or the last +n+ records, from the collection.
       # If the collection is empty, the first form returns +nil+, and the second
       # form returns an empty array.
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 1f429cfd94..5259797223 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -1,7 +1,7 @@
 module ActiveRecord
   module Querying
     delegate :find, :take, :take!, :first, :first!, :last, :last!, :exists?, :any?, :many?, to: :all
-    delegate :second, :second!, :third, :third!, :fourth, :fourth!, :fifth, :fifth!, :forty_two, :forty_two!, to: :all
+    delegate :second, :second!, :third, :third!, :fourth, :fourth!, :fifth, :fifth!, :forty_two, :forty_two!, :third_to_last, :third_to_last!, :second_to_last, :second_to_last!, to: :all
     delegate :first_or_create, :first_or_create!, :first_or_initialize, to: :all
     delegate :find_or_create_by, :find_or_create_by!, :find_or_initialize_by, to: :all
     delegate :find_by, :find_by!, to: :all
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index d48bcea28a..90a6a466fd 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -242,6 +242,38 @@ module ActiveRecord
       find_nth! 41
     end
 
+    # Find the third-to-last record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.third_to_last # returns the third-to-last object fetched by SELECT * FROM people
+    #   Person.offset(3).third_to_last # returns the third-to-last object from OFFSET 3
+    #   Person.where(["user_name = :u", { u: user_name }]).third_to_last
+    def third_to_last
+      find_nth -3
+    end
+
+    # Same as #third_to_last but raises ActiveRecord::RecordNotFound if no record
+    # is found.
+    def third_to_last!
+      find_nth! -3
+    end
+
+    # Find the second-to-last record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.second_to_last # returns the second-to-last object fetched by SELECT * FROM people
+    #   Person.offset(3).second_to_last # returns the second-to-last object from OFFSET 3
+    #   Person.where(["user_name = :u", { u: user_name }]).second_to_last
+    def second_to_last
+      find_nth -2
+    end
+
+    # Same as #second_to_last but raises ActiveRecord::RecordNotFound if no record
+    # is found.
+    def second_to_last!
+      find_nth! -2
+    end
+
     # Returns true if a record exists in the table that matches the +id+ or
     # conditions given, or false otherwise. The argument can take six forms:
     #
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index ecaa521283..e975f4fbdd 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -408,6 +408,16 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
 
     assert_no_queries do
+      bulbs.third_to_last()
+      bulbs.third_to_last({})
+    end
+
+    assert_no_queries do
+      bulbs.second_to_last()
+      bulbs.second_to_last({})
+    end
+
+    assert_no_queries do
       bulbs.last()
       bulbs.last({})
     end
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index bd333da081..3d4cc8fae6 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add `Array#second_to_last` and `Array#third_to_last` methods.
+
+    *Brian Christian*
+
 *  Fix regression in `Hash#dig` for HashWithIndifferentAccess.
    *Jon Moss*
 
diff --git a/activesupport/lib/active_support/core_ext/array/access.rb b/activesupport/lib/active_support/core_ext/array/access.rb
index 3177d8498e..37d833887a 100644
--- a/activesupport/lib/active_support/core_ext/array/access.rb
+++ b/activesupport/lib/active_support/core_ext/array/access.rb
@@ -73,4 +73,18 @@ class Array
   def forty_two
     self[41]
   end
+
+  # Equal to <tt>self[-3]</tt>.
+  #
+  #   %w( a b c d e ).third_to_last # => "c"
+  def third_to_last
+    self[-3]
+  end
+
+  # Equal to <tt>self[-2]</tt>.
+  #
+  #   %w( a b c d e ).second_to_last # => "d"
+  def second_to_last
+    self[-2]
+  end
 end
diff --git a/activesupport/test/core_ext/array/access_test.rb b/activesupport/test/core_ext/array/access_test.rb
index 3f1e0c4cb4..1d834667f0 100644
--- a/activesupport/test/core_ext/array/access_test.rb
+++ b/activesupport/test/core_ext/array/access_test.rb
@@ -26,6 +26,8 @@ class AccessTest < ActiveSupport::TestCase
     assert_equal array[3], array.fourth
     assert_equal array[4], array.fifth
     assert_equal array[41], array.forty_two
+    assert_equal array[-3], array.third_to_last
+    assert_equal array[-2], array.second_to_last
   end
 
   def test_without
diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index 0aca6db9b6..10122629b2 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -2240,7 +2240,7 @@ Similarly, `from` returns the tail from the element at the passed index to the e
 [].from(0)           # => []
 ```
 
-The methods `second`, `third`, `fourth`, and `fifth` return the corresponding element (`first` is built-in). Thanks to social wisdom and positive constructiveness all around, `forty_two` is also available.
+The methods `second`, `third`, `fourth`, and `fifth` return the corresponding element, as do `second_to_last` and `third_to_last` (`first` and `last` are built-in). Thanks to social wisdom and positive constructiveness all around, `forty_two` is also available.
 
 ```ruby
 %w(a b c d).third # => "c"