What causes undefined method `map!' for ActiveRecord_Relation?

Question

I am updating from Rails 3 to Rails 4.2, and when I run my application's test suite, I get the following error:

 Failure/Error: get 'edit', id: @shops[3].id
 NoMethodError:
   undefined method `map!' for #<Shop::ActiveRecord_Relation:0x007ff1d69b4f40>

The code in the controller is:

existing_shops.map! { |obj| [["##{obj[:shop_id]} #{obj[:name]},
#{obj[:phone]}, #{obj[:address]}, #{obj[:city]}, #{obj[:state]}, #{obj[:zipcode]} "]]}

I am using Rails 4.2.4 and RSpec 3.3.0.

Answer 1

Relation no longer has mutator methods like #map! and #delete_if. Convert to an Array by calling #to_a before using these methods.

existing_shops.to_a.map! { ... }

— A Guide for Upgrading Ruby on Rails