Merge pull request #13314 from laurocaetano/blacklist_array_methods

Create a blacklist to disallow mutator methods to be delegated to Array

Conflicts:
	guides/source/upgrading_ruby_on_rails.md

1 files changed, 17 insertions, 0 deletions

diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index b838874e2b..33e58f892e 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -200,6 +200,23 @@ Note that this option was added as a security measure, to ensure user input coul
 not be used as locale information unless previously known, so it's recommended not
 to disable this option unless you have a strong reason for doing so.
 
+### Mutator methods called on Relation
+
+`Relation` no longer has mutator methods like `#map!` and `#delete_if`. Convert
+to an `Array` by calling `#to_a` before using these methods.
+
+It intends to prevent odd bugs and confusion in code that call mutator
+methods directly on the `Relation`.
+
+```ruby
+# Instead of this
+Author.where(name: 'Hank Moody').compact!
+
+# Now you have to do this
+authors = Author.where(name: 'Hank Moody').to_a
+authors.compact!
+```
+
 Upgrading from Rails 3.2 to Rails 4.0
 -------------------------------------