Better support for `where()` conditions that use an association name.

Using the name of an association in `where` previously worked only
if the value was a single `ActiveRecrd::Base` object. e.g.

    Post.where(author: Author.first)

Any other values, including `nil`, would cause invalid SQL to be
generated. This change supports arguments in the `where` query
conditions where the key is a `belongs_to` association name and the
value is `nil`, an `Array` of `ActiveRecord::Base` objects, or an
`ActiveRecord::Relation` object.

    # Given the Post model
    class Post < ActiveRecord::Base
      belongs_to :author
    end

    # nil value finds records where the association is not set
    Post.where(author: nil)
    # SELECT "posts".* FROM "posts" WHERE "posts"."author_id" IS NULL

    # Array values find records where the association foreign key
    # matches the ids of the passed ActiveRecord models, resulting
    # in the same query as Post.where(author_id: [1,2])
    authors_array = [Author.find(1), Author.find(2)]
    Post.where(author: authors_array)

    # ActiveRecord::Relation values find records using the same
    # query as Post.where(author_id: Author.where(last_name: "Emde"))
    Post.where(author: Author.where(last_name: "Emde"))

Polymorphic `belongs_to` associations will continue to be handled
appropriately, with the polymorphic `association_type` field added
to the query to match the base class of the value. This feature
previously only worked when the value was a single `ActveRecord::Base`.

    class Post < ActiveRecord::Base
      belongs_to :author, polymorphic: true
    end

    Post.where(author: Author.where(last_name: "Emde"))
    # Generates a query similar to:
    Post.where(author_id: Author.where(last_name: "Emde"), author_type: "Author")

1 files changed, 34 insertions, 0 deletions

diff --git a/activerecord/test/cases/relation/where_test.rb b/activerecord/test/cases/relation/where_test.rb
index 56e4605ccc..937f226b1d 100644
--- a/activerecord/test/cases/relation/where_test.rb
+++ b/activerecord/test/cases/relation/where_test.rb
@@ -35,6 +35,21 @@ module ActiveRecord
       assert_equal Post.where(author_id: 1).to_sql, Post.where(author: author).to_sql
     end
 
+    def test_belongs_to_nil_where
+      assert_equal Post.where(author_id: nil).to_sql, Post.where(author: nil).to_sql
+    end
+
+    def test_belongs_to_array_value_where
+      assert_equal Post.where(author_id: [1,2]).to_sql, Post.where(author: [1,2]).to_sql
+    end
+
+    def test_belongs_to_nested_relation_where
+      expected = Post.where(author_id: Author.where(id: [1,2])).to_sql
+      actual   = Post.where(author:    Author.where(id: [1,2])).to_sql
+
+      assert_equal expected, actual
+    end
+
     def test_belongs_to_nested_where
       parent = Comment.new
       parent.id = 1
@@ -55,6 +70,25 @@ module ActiveRecord
       assert_equal expected.to_sql, actual.to_sql
     end
 
+    def test_polymorphic_nested_array_where
+      treasure = Treasure.new
+      treasure.id = 1
+      hidden = HiddenTreasure.new
+      hidden.id = 2
+
+      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: [treasure, hidden])
+      actual   = PriceEstimate.where(estimate_of: [treasure, hidden])
+
+      assert_equal expected.to_sql, actual.to_sql
+    end
+
+    def test_polymorphic_nested_relation_where
+      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: Treasure.where(id: [1,2]))
+      actual   = PriceEstimate.where(estimate_of: Treasure.where(id: [1,2]))
+
+      assert_equal expected.to_sql, actual.to_sql
+    end
+
     def test_polymorphic_sti_shallow_where
       treasure = HiddenTreasure.new
       treasure.id = 1