Fix has_many through association assginments with custom scope and custom joining association name

`where_values_hash` method signature accepts `table_name` which is not
always the same as the association name.
So passing `through_association.reflection.name.to_s` as `table_name`
in `through_scope_attributes` wasn't accurate for every case.
This commit fixes the issue by passing the `table_name` taken from
`through_association.reflection.klass.table_name` instead.

Author: nvasilevski

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -70,7 +70,7 @@ def build_through_record(record)
 
         def through_scope_attributes
           scope = through_scope || self.scope
-          attributes = scope.where_values_hash(through_association.reflection.name.to_s)
+          attributes = scope.where_values_hash(through_association.reflection.klass.table_name)
           except_keys = [
             *Array(through_association.reflection.foreign_key),
             through_association.reflection.klass.inheritance_column

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -1359,6 +1359,18 @@ def test_insert_records_via_has_many_through_association_with_scope
     assert_equal [member], club.favorites
   end
 
+  def test_insert_records_via_has_many_through_association_with_scope_and_association_name_different_from_the_joining_table_name
+    club = Club.create!
+    member = Member.create!
+    Membership.create!(club: club, member: member)
+
+    club.custom_favorites << member
+    assert_equal [member], club.custom_favorites
+
+    club.reload
+    assert_equal [member], club.custom_favorites
+  end
+
   def test_has_many_through_unscope_default_scope
     post = Post.create!(title: "Beaches", body: "I like beaches!")
     Reader.create! person: people(:david), post: post

activerecord/test/models/club.rb

@@ -10,6 +10,9 @@ class Club < ActiveRecord::Base
 
   has_many :favorites, -> { where(memberships: { favorite: true }) }, through: :memberships, source: :member
 
+  has_many :custom_memberships, class_name: "Membership"
+  has_many :custom_favorites, -> { where(memberships: { favorite: true }) }, through: :custom_memberships, source: :member
+
   scope :general, -> { left_joins(:category).where(categories: { name: "General" }).unscope(:limit) }
 
   accepts_nested_attributes_for :membership