fk: add docs

1 files changed, 25 insertions, 0 deletions

diff --git a/guides/source/4_2_release_notes.md b/guides/source/4_2_release_notes.md
index dd484ccee2..ef294f55d7 100644
--- a/guides/source/4_2_release_notes.md
+++ b/guides/source/4_2_release_notes.md
@@ -25,6 +25,31 @@ guide.
 Major Features
 --------------
 
+### Foreign key support
+
+The migration DSL now supports adding and removing foreign keys. They are dumped
+to `schema.rb` as well. At this time, only the `mysql`, `mysql2` and `postgresql`
+adapters support foreign keys.
+
+```ruby
+# add a foreign key to `articles.author_id` referencing `authors.id`
+add_foreign_key :articles, :authors
+
+# add a foreign key to `articles.author_id` referencing `users.lng_id`
+add_foreign_key :articles, :users, column: :author_id, primary_key: "lng_id"
+
+# remove the foreign key on `accounts.branch_id`
+remove_foreign_key :accounts, :branches
+
+# remove the foreign key on `accounts.owner_id`
+remove_foreign_key :accounts, column: :owner_id
+```
+
+See the API documentation on
+[add_foreign_key](http://api.rubyonrails.org/v4.2.0/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-add_foreign_key)
+and
+[remove_foreign_key](http://api.rubyonrails.org/v4.2.0/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-remove_foreign_key)
+for a full description.
 
 
 Railties