Add Read-Only Models as a rails til

rails/read-only-models.md

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+# Read-Only Models
+
+Are you in the midst of a big refactoring that is phasing out an
+`ActiveRecord` model? You may not be ready to wipe it from the project, but
+you don't want it accidentally used to create any database records. You
+essentially want your model to be read-only until it is time to actually
+delete it.
+
+This can be achieved by adding a `readonly?` method to that model that
+always returns `true`.
+
+```ruby
+def readonly?
+  true
+end
+```
+
+`ActiveRecord`'s underlying persistence methods always check `readonly?`
+before creating or updating any records.
+
+[source](http://stackoverflow.com/questions/5641410/is-there-an-easy-way-to-make-a-rails-activerecord-model-read-only)
+
+h/t Josh Davey