Optimize ActiveRecord::Relation#include? on an unloaded relation

Perform an efficient existence query through #exists? instead of loading the entire relation into memory and searching it.

Before:

    > Person.where(name: "David").include?(david)
    SELECT `people`.* FROM `people` WHERE `people`.`name` = 'David'
    => true

After:

    > Person.where(name: "David").include?(david)
    SELECT 1 AS one FROM `people` WHERE `people`.`name` = 'David' AND `people`.`id` = 1 LIMIT 1
    => true

activerecord/lib/active_record/relation/finder_methods.rb

@@ -319,6 +319,21 @@ module ActiveRecord
       skip_query_cache_if_necessary { connection.select_rows(relation.arel, "#{name} Exists?").size == 1 }
     end
 
+    # Returns true if the relation contains the given record or false otherwise.
+    #
+    # No query is performed if the relation is loaded; the given record is
+    # compared to the records in memory. If the relation is unloaded, an
+    # efficient existence query is performed, as in #exists?.
+    def include?(record)
+      if loaded?
+        records.include?(record)
+      else
+        record.is_a?(klass) && exists?(record.id)
+      end
+    end
+
+    alias :member? :include?
+
     # This method is called whenever no records are found with either a single
     # id or multiple ids and raises an ActiveRecord::RecordNotFound exception.
     #

activerecord/test/cases/finder_test.rb

@@ -375,6 +375,84 @@ class FinderTest < ActiveRecord::TestCase
     end
   end
 
+  def test_include_on_unloaded_relation_with_match
+    assert_sql(/1 AS one.*LIMIT/) do
+      assert_equal true, Customer.where(name: "David").include?(customers(:david))
+    end
+  end
+
+  def test_include_on_unloaded_relation_without_match
+    assert_sql(/1 AS one.*LIMIT/) do
+      assert_equal false, Customer.where(name: "David").include?(customers(:mary))
+    end
+  end
+
+  def test_include_on_unloaded_relation_with_mismatched_class
+    topic = topics(:first)
+    assert Customer.exists?(topic.id)
+
+    assert_no_queries do
+      assert_equal false, Customer.where(name: "David").include?(topic)
+    end
+  end
+
+  def test_include_on_loaded_relation_with_match
+    customers = Customer.where(name: "David").load
+    david     = customers(:david)
+
+    assert_no_queries do
+      assert_equal true, customers.include?(david)
+    end
+  end
+
+  def test_include_on_loaded_relation_without_match
+    customers = Customer.where(name: "David").load
+    mary      = customers(:mary)
+
+    assert_no_queries do
+      assert_equal false, customers.include?(mary)
+    end
+  end
+
+  def test_member_on_unloaded_relation_with_match
+    assert_sql(/1 AS one.*LIMIT/) do
+      assert_equal true, Customer.where(name: "David").member?(customers(:david))
+    end
+  end
+
+  def test_member_on_unloaded_relation_without_match
+    assert_sql(/1 AS one.*LIMIT/) do
+      assert_equal false, Customer.where(name: "David").member?(customers(:mary))
+    end
+  end
+
+  def test_member_on_unloaded_relation_with_mismatched_class
+    topic = topics(:first)
+    assert Customer.exists?(topic.id)
+
+    assert_no_queries do
+      assert_equal false, Customer.where(name: "David").member?(topic)
+    end
+  end
+
+  def test_member_on_loaded_relation_with_match
+    customers = Customer.where(name: "David").load
+    david     = customers(:david)
+
+    assert_no_queries do
+      assert_equal true, customers.member?(david)
+    end
+  end
+
+  def test_member_on_loaded_relation_without_match
+    customers = Customer.where(name: "David").load
+    mary      = customers(:mary)
+
+    assert_no_queries do
+      assert_equal false, customers.member?(mary)
+    end
+  end
+
   def test_find_by_array_of_one_id
     assert_kind_of(Array, Topic.find([ 1 ]))
     assert_equal(1, Topic.find([ 1 ]).length)

activerecord/test/cases/relation/delegation_test.rb

@@ -48,7 +48,7 @@ module ActiveRecord
     QUERYING_METHODS =
       ActiveRecord::Batches.public_instance_methods(false) +
       ActiveRecord::Calculations.public_instance_methods(false) +
-      ActiveRecord::FinderMethods.public_instance_methods(false) - [:raise_record_not_found_exception!] +
+      ActiveRecord::FinderMethods.public_instance_methods(false) - [:include?, :member?, :raise_record_not_found_exception!] +
       ActiveRecord::SpawnMethods.public_instance_methods(false) - [:spawn, :merge!] +
       ActiveRecord::QueryMethods.public_instance_methods(false).reject { |method|
         method.end_with?("=", "!", "value", "values", "clause")