Merge pull request #16314 from zoltankiss/allow-nested-has-many-assoc…

…iations-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 @@ def stale_state
        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 @@ def clear_association_scope_cache # :nodoc:
        @association_scope_cache.clear
      end

      def belongs_to_or_through?
        belongs_to?
      end

      def nested?
        false
      end
@@ -836,6 +840,10 @@ def join_scopes(table, predicate_builder) # :nodoc:
        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 @@ def test_incorrectly_ordered_through_associations
    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 } }