Add ActiveRecord::Relation#in_batches

`in_batches` yields Relation objects if a block is given, otherwise it
returns an instance of `BatchEnumerator`. The existing `find_each` and
`find_in_batches` methods work with batches of records. The new API
allows working with relation batches as well.

Examples:

    Person.in_batches.each_record(&:party_all_night!)
    Person.in_batches.update_all(awesome: true)
    Person.in_batches.delete_all
    Person.in_batches.map do |relation|
      relation.delete_all
      sleep 10 # Throttles the delete queries
    end

1 files changed, 230 insertions, 2 deletions

diff --git a/activerecord/test/cases/batches_test.rb b/activerecord/test/cases/batches_test.rb
index 0791dde1f2..48dc8135ab 100644
--- a/activerecord/test/cases/batches_test.rb
+++ b/activerecord/test/cases/batches_test.rb
@@ -53,7 +53,7 @@ class EachTest < ActiveRecord::TestCase
   end
 
   def test_each_should_raise_if_select_is_set_without_id
-    assert_raise(RuntimeError) do
+    assert_raise(ArgumentError) do
       Post.select(:title).find_each(batch_size: 1) { |post|
         flunk "should not call this block"
       }
@@ -199,7 +199,7 @@ class EachTest < ActiveRecord::TestCase
 
   def test_find_in_batches_should_return_an_enumerator
     enum = nil
-    assert_queries(0) do
+    assert_no_queries do
       enum = Post.find_in_batches(:batch_size => 1)
     end
     assert_queries(4) do
@@ -210,6 +210,234 @@ class EachTest < ActiveRecord::TestCase
     end
   end
 
+  def test_in_batches_should_not_execute_any_query
+    assert_no_queries do
+      assert_kind_of ActiveRecord::Batches::BatchEnumerator, Post.in_batches(of: 2)
+    end
+  end
+
+  def test_in_batches_should_yield_relation_if_block_given
+    assert_queries(6) do
+      Post.in_batches(of: 2) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+      end
+    end
+  end
+
+  def test_in_batches_should_be_enumerable_if_no_block_given
+    assert_queries(6) do
+      Post.in_batches(of: 2).each do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+      end
+    end
+  end
+
+  def test_in_batches_each_record_should_yield_record_if_block_is_given
+    assert_queries(6) do
+      Post.in_batches(of: 2).each_record do |post|
+        assert post.title.present?
+        assert_kind_of Post, post
+      end
+    end
+  end
+
+  def test_in_batches_each_record_should_return_enumerator_if_no_block_given
+    assert_queries(6) do
+      Post.in_batches(of: 2).each_record.with_index do |post, i|
+        assert post.title.present?
+        assert_kind_of Post, post
+      end
+    end
+  end
+
+  def test_in_batches_each_record_should_be_ordered_by_id
+    ids = Post.order('id ASC').pluck(:id)
+    assert_queries(6) do
+      Post.in_batches(of: 2).each_record.with_index do |post, i|
+        assert_equal ids[i], post.id
+      end
+    end
+  end
+
+  def test_in_batches_update_all_affect_all_records
+    assert_queries(6 + 6) do # 6 selects, 6 updates
+      Post.in_batches(of: 2).update_all(title: "updated-title")
+    end
+    assert_equal Post.all.pluck(:title), ["updated-title"] * Post.count
+  end
+
+  def test_in_batches_delete_all_should_not_delete_records_in_other_batches
+    not_deleted_count = Post.where('id <= 2').count
+    Post.where('id > 2').in_batches(of: 2).delete_all
+    assert_equal 0, Post.where('id > 2').count
+    assert_equal not_deleted_count, Post.count
+  end
+
+  def test_in_batches_should_not_be_loaded
+    Post.in_batches(of: 1) do |relation|
+      assert_not relation.loaded?
+    end
+
+    Post.in_batches(of: 1, load: false) do |relation|
+      assert_not relation.loaded?
+    end
+  end
+
+  def test_in_batches_should_be_loaded
+    Post.in_batches(of: 1, load: true) do |relation|
+      assert relation.loaded?
+    end
+  end
+
+  def test_in_batches_if_not_loaded_executes_more_queries
+    assert_queries(@total + 1) do
+      Post.in_batches(of: 1, load: false) do |relation|
+        assert_not relation.loaded?
+      end
+    end
+  end
+
+  def test_in_batches_should_return_relations
+    assert_queries(@total + 1) do
+      Post.in_batches(of: 1) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+      end
+    end
+  end
+
+  def test_in_batches_should_start_from_the_start_option
+    post = Post.order('id ASC').where('id >= ?', 2).first
+    assert_queries(2) do
+      relation = Post.in_batches(of: 1, begin_at: 2).first
+      assert_equal post, relation.first
+    end
+  end
+
+  def test_in_batches_should_end_at_the_end_option
+    post = Post.order('id DESC').where('id <= ?', 5).first
+    assert_queries(7) do
+      relation = Post.in_batches(of: 1, end_at: 5, load: true).reverse_each.first
+      assert_equal post, relation.last
+    end
+  end
+
+  def test_in_batches_shouldnt_execute_query_unless_needed
+    assert_queries(2) do
+      Post.in_batches(of: @total) { |relation| assert_kind_of ActiveRecord::Relation, relation }
+    end
+
+    assert_queries(1) do
+      Post.in_batches(of: @total + 1) { |relation| assert_kind_of ActiveRecord::Relation, relation }
+    end
+  end
+
+  def test_in_batches_should_quote_batch_order
+    c = Post.connection
+    assert_sql(/ORDER BY #{c.quote_table_name('posts')}.#{c.quote_column_name('id')}/) do
+      Post.in_batches(of: 1) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Post, relation.first
+      end
+    end
+  end
+
+  def test_in_batches_should_not_use_records_after_yielding_them_in_case_original_array_is_modified
+    not_a_post = "not a post"
+    def not_a_post.id
+      raise StandardError.new("not_a_post had #id called on it")
+    end
+
+    assert_nothing_raised do
+      Post.in_batches(of: 1) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Post, relation.first
+
+        relation = [not_a_post] * relation.count
+      end
+    end
+  end
+
+  def test_in_batches_should_not_ignore_default_scope_without_order_statements
+    special_posts_ids = SpecialPostWithDefaultScope.all.map(&:id).sort
+    posts = []
+    SpecialPostWithDefaultScope.in_batches do |relation|
+      posts.concat(relation)
+    end
+    assert_equal special_posts_ids, posts.map(&:id)
+  end
+
+  def test_in_batches_should_not_modify_passed_options
+    assert_nothing_raised do
+      Post.in_batches({ of: 42, begin_at: 1 }.freeze){}
+    end
+  end
+
+  def test_in_batches_should_use_any_column_as_primary_key
+    nick_order_subscribers = Subscriber.order('nick asc')
+    start_nick = nick_order_subscribers.second.nick
+
+    subscribers = []
+    Subscriber.in_batches(of: 1, begin_at: start_nick) do |relation|
+      subscribers.concat(relation)
+    end
+
+    assert_equal nick_order_subscribers[1..-1].map(&:id), subscribers.map(&:id)
+  end
+
+  def test_in_batches_should_use_any_column_as_primary_key_when_start_is_not_specified
+    assert_queries(Subscriber.count + 1) do
+      Subscriber.in_batches(of: 1, load: true) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Subscriber, relation.first
+      end
+    end
+  end
+
+  def test_in_batches_should_return_an_enumerator
+    enum = nil
+    assert_no_queries do
+      enum = Post.in_batches(of: 1)
+    end
+    assert_queries(4) do
+      enum.first(4) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Post, relation.first
+      end
+    end
+  end
+
+  def test_in_batches_relations_should_not_overlap_with_each_other
+    seen_posts = []
+    Post.in_batches(of: 2, load: true) do |relation|
+      relation.to_a.each do |post|
+        assert_not seen_posts.include?(post)
+        seen_posts << post
+      end
+    end
+  end
+
+  def test_in_batches_relations_with_condition_should_not_overlap_with_each_other
+    seen_posts = []
+    author_id = Post.first.author_id
+    posts_by_author = Post.where(author_id: author_id)
+    Post.in_batches(of: 2) do |batch|
+      seen_posts += batch.where(author_id: author_id)
+    end
+
+    assert_equal posts_by_author.pluck(:id).sort, seen_posts.map(&:id).sort
+  end
+
+  def test_in_batches_relations_update_all_should_not_affect_matching_records_in_other_batches
+    Post.update_all(author_id: 0)
+    person = Post.last
+    person.update_attributes(author_id: 1)
+
+    Post.in_batches(of: 2) do |batch|
+      batch.where('author_id >= 1').update_all('author_id = author_id + 1')
+    end
+    assert_equal 2, person.reload.author_id # incremented only once
+  end
+
   def test_find_in_batches_start_deprecated
     assert_deprecated do
       assert_queries(@total) do