Merge pull request #46 from zenspongebob/update-readme

Add readme entry for many to many associations

README.md

@@ -106,6 +106,41 @@ You need to specicfy `type` option
     end
 ```
 
+### Many to many associations
+
+Please note that this library doesn't work properly with `has_and_belongs_to_many` associations.
+
+Our recommendation is to be explicit and instead use the `has_many, through: join_class` association. 
+Notice that for it to work properly you must specify the `has_many` to the join class in the main classes of the association,
+and your join class must have `belongs_to` main classes defined as shown in the example below:
+
+```ruby
+  class User < ActiveRecord::Base
+    include ULID::Rails
+    ulid :id, auto_generate: true
+
+    has_many :user_articles
+    has_many :articles, through: :user_articles
+  end
+
+  class UserArticle < ActiveRecord::Base
+    include ULID::Rails
+    ulid :id, auto_generate: true
+    ulid :user_id
+    ulid :article_id
+
+    belongs_to :user
+    belongs_to :article
+  end
+
+  class Article < ActiveRecord::Base
+    include ULID::Rails
+    ulid :id, auto_generate: true
+
+    has_many :user_articles
+  end
+```
+
 ## Development
 
 ### Run tests