Merge pull request #16314 from zoltankiss/allow-nested-has-many-associations-on-unpersisted-parent-instances

fix nested `has many :through` associations on unpersisted parent instances

activerecord/CHANGELOG.md

@@ -1,3 +1,41 @@
+*   Fix nested `has_many :through` associations on unpersisted parent instances.
+
+    For example, if you have
+
+        class Post < ActiveRecord::Base
+          belongs_to :author
+          has_many :books, through: :author
+          has_many :subscriptions, through: :books
+        end
+
+        class Author < ActiveRecord::Base
+          has_one :post
+          has_many :books
+          has_many :subscriptions, through: :books
+        end
+
+        class Book < ActiveRecord::Base
+          belongs_to :author
+          has_many :subscriptions
+        end
+
+        class Subscription < ActiveRecord::Base
+          belongs_to :book
+        end
+
+    Before:
+
+    If `post` is not persisted, then `post.subscriptions` will be empty.
+
+    After:
+
+    If `post` is not persisted, then `post.subscriptions` can be set and used
+    just like it would if `post` were persisted.
+
+    Fixes #16313.
+
+    *Zoltan Kiss*
+
 *   Fixed inconsistency with `first(n)` when used with `limit()`.
     The `first(n)` finder now respects the `limit()`, making it consistent
     with `relation.to_a.first(n)`, and also with the behavior of `last(n)`.

activerecord/lib/active_record/associations/through_association.rb

@@ -68,7 +68,7 @@ module ActiveRecord
         end
 
         def foreign_key_present?
-          through_reflection.belongs_to? && !owner[through_reflection.foreign_key].nil?
+          through_reflection.belongs_to_or_through? && !owner[through_reflection.foreign_key].nil?
         end
 
         def ensure_mutable

activerecord/lib/active_record/reflection.rb

@@ -504,6 +504,10 @@ module ActiveRecord
         @association_scope_cache.clear
       end
 
+      def belongs_to_or_through?
+        belongs_to?
+      end
+
       def nested?
         false
       end
@@ -836,6 +840,10 @@ module ActiveRecord
         source_reflection.join_scopes(table, predicate_builder) + super
       end
 
+      def belongs_to_or_through?
+        through_reflection.belongs_to_or_through?
+      end
+
       def has_scope?
         scope || options[:source_type] ||
           source_reflection.has_scope? ||

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -1308,6 +1308,35 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
   end
 
+  def test_single_has_many_through_association_with_unpersisted_parent_instance
+    post_with_single_has_many_through = Class.new(Post) do
+      def self.name; "PostWithSingleHasManyThrough"; end
+      has_many :subscriptions, through: :author
+    end
+    post = post_with_single_has_many_through.new
+    post.author = Author.create!(name: "Federico Morissette")
+    book = Book.create!(name: "essays on single has many through associations")
+    post.author.books << book
+    subscription = Subscription.first
+    book.subscriptions << subscription
+    assert_equal [subscription], post.subscriptions.to_a
+  end
+
+  def test_nested_has_many_through_association_with_unpersisted_parent_instance
+    post_with_nested_has_many_through = Class.new(Post) do
+      def self.name; "PostWithNestedHasManyThrough"; end
+      has_many :books, through: :author
+      has_many :subscriptions, through: :books
+    end
+    post = post_with_nested_has_many_through.new
+    post.author = Author.create!(name: "Obie Weissnat")
+    book = Book.create!(name: "essays on nested has many through associations")
+    post.author.books << book
+    subscription = Subscription.first
+    book.subscriptions << subscription
+    assert_equal [subscription], post.subscriptions.to_a
+  end
+
   private
     def make_model(name)
       Class.new(ActiveRecord::Base) { define_singleton_method(:name) { name } }