Added comments about the check_empty_arguments method which is called

for query methods in a where_clause. Also, modified the CHANGELOG entry
because it had false information and added tests.

3 files changed, 45 insertions, 15 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index a888b79391..60ebe2ff7c 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -6,13 +6,11 @@
     *Yves Senn*
 
 *   ActiveRecord now raises an error when blank arguments are passed to query
-    methods for which blank arguments do not make sense. This also occurs for
-    nil-like objects in arguments.
+    methods for which blank arguments do not make sense.
 
     Example:
 
-        Post.limit()     # => raises error
-        Post.include([]) # => raises error
+        Post.includes()     # => raises error
 
     *John Wang*
 
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 85534608ac..5358b43728 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -108,7 +108,7 @@ module ActiveRecord
     #
     #   User.includes(:posts).where('posts.name = ?', 'example').references(:posts)
     def includes(*args)
-      check_empty_arguments("includes", *args)
+      check_empty_arguments("includes", args)
       spawn.includes!(*args)
     end
 
@@ -126,7 +126,7 @@ module ActiveRecord
     #   FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" =
     #   "users"."id"
     def eager_load(*args)
-      check_empty_arguments("eager_load", *args)
+      check_empty_arguments("eager_load", args)
       spawn.eager_load!(*args)
     end
 
@@ -140,7 +140,7 @@ module ActiveRecord
     #   User.preload(:posts)
     #   => SELECT "posts".* FROM "posts" WHERE "posts"."user_id" IN (1, 2, 3)
     def preload(*args)
-      check_empty_arguments("preload", *args)
+      check_empty_arguments("preload", args)
       spawn.preload!(*args)
     end
 
@@ -158,7 +158,7 @@ module ActiveRecord
     #   User.includes(:posts).where("posts.name = 'foo'").references(:posts)
     #   # => Query now knows the string references posts, so adds a JOIN
     def references(*args)
-      check_empty_arguments("references", *args)
+      check_empty_arguments("references", args)
       spawn.references!(*args)
     end
 
@@ -238,7 +238,7 @@ module ActiveRecord
     #   User.group('name AS grouped_name, age')
     #   => [#<User id: 3, name: "Foo", age: 21, ...>, #<User id: 2, name: "Oscar", age: 21, ...>, #<User id: 5, name: "Foo", age: 23, ...>]
     def group(*args)
-      check_empty_arguments("group", *args)
+      check_empty_arguments("group", args)
       spawn.group!(*args)
     end
 
@@ -269,7 +269,7 @@ module ActiveRecord
     #   User.order(:name, email: :desc)
     #   => SELECT "users".* FROM "users" ORDER BY "users"."name" ASC, "users"."email" DESC
     def order(*args)
-      check_empty_arguments("order", *args)
+      check_empty_arguments("order", args)
       spawn.order!(*args)
     end
 
@@ -295,7 +295,7 @@ module ActiveRecord
     #
     # generates a query with 'ORDER BY name ASC, id ASC'.
     def reorder(*args)
-      check_empty_arguments("reorder", *args)
+      check_empty_arguments("reorder", args)
       spawn.reorder!(*args)
     end
 
@@ -318,8 +318,8 @@ module ActiveRecord
     #   User.joins("LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id")
     #   => SELECT "users".* FROM "users" LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id
     def joins(*args)
-      check_empty_arguments("joins", *args)
-      spawn.joins!(*args.flatten)
+      check_empty_arguments("joins", args)
+      spawn.joins!(*args.compact.flatten)
     end
 
     def joins!(*args) # :nodoc:
@@ -483,7 +483,7 @@ module ActiveRecord
     #
     #   Order.having('SUM(price) > 30').group('user_id')
     def having(opts, *rest)
-      check_empty_arguments("having", opts)
+      opts.blank? ? self : spawn.having!(opts, *rest)
       spawn.having!(opts, *rest)
     end
 
@@ -921,7 +921,23 @@ module ActiveRecord
       end
     end
 
-    def check_empty_arguments(method_name, *args)
+    # Checks to make sure that the arguments are not blank. Note that if some
+    # blank-like object were initially passed into the query method, then this
+    # method will not raise an error.
+    #
+    # Example:
+    #
+    #    Post.references()   # => raises an error
+    #    Post.references([]) # => does not raise an error
+    #
+    # This particular method should be called with a method_name and the args
+    # passed into that method as an input. For example:
+    #
+    # def references(*args)
+    #   check_empty_arguments("references", args)
+    #   ...
+    # end
+    def check_empty_arguments(method_name, args)
       if args.blank?
         raise ArgumentError, "The method .#{method_name}() must contain arguments."
       end
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 379c0c0758..8298d7534c 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -321,6 +321,22 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal 1, person_with_reader_and_post.size
   end
 
+  def test_no_arguments_to_query_methods_raise_errors
+    assert_raises(ArgumentError) { Topic.references() }
+    assert_raises(ArgumentError) { Topic.includes() }
+    assert_raises(ArgumentError) { Topic.preload() }
+    assert_raises(ArgumentError) { Topic.group() }
+    assert_raises(ArgumentError) { Topic.reorder() }
+  end
+
+  def test_blank_like_arguments_to_query_methods_dont_raise_errors
+    assert_nothing_raised { Topic.references([]) }
+    assert_nothing_raised { Topic.includes([]) }
+    assert_nothing_raised { Topic.preload([]) }
+    assert_nothing_raised { Topic.group([]) }
+    assert_nothing_raised { Topic.reorder([]) }
+  end
+
   def test_scoped_responds_to_delegated_methods
     relation = Topic.all