Add Read-Only Models as a rails til

Author: jbranchaud

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_431 TILs and counting..._
+_432 TILs and counting..._
 
 ---
 
@@ -278,6 +278,7 @@ _431 TILs and counting..._
 - [Params Includes Submission Button Info](rails/params-includes-submission-button-info.md)
 - [Perform SQL Explain With ActiveRecord](rails/perform-sql-explain-with-activerecord.md)
 - [Pretend Generations](rails/pretend-generations.md)
+- [Read-Only Models](rails/read-only-models.md)
 - [Rescue From](rails/rescue-from.md)
 - [Retrieve An Object If It Exists](rails/retrieve-an-object-if-it-exists.md)
 - [Select A Select By Selector](rails/select-a-select-by-selector.md)

rails/read-only-models.md

@@ -0,0 +1,23 @@
+# 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