Performance regression.

[arthurnn]

Problem

define_attribute_methods is slow, AR.respond_to? call that method, in every call: https://github.com/rails/rails/blob/4-0-stable/activerecord/lib/active_record/attribute_methods.rb#L202

this was introduced after https://github.com/rails/rails/commit/30efdd6e9066684dc952966ed71e23a9c7640e7e .

Solution

Make sure we dont define the methods more than one time. Almost the same way that AR does.

Benchmark using mysql+shopify Gemfile

Before:
       user     system      total        real
  18.800000  81.110000  99.910000 (112.324601)
After:
       user     system      total        real
   2.310000  31.300000  33.610000 ( 40.771561)

Benchmark using sqlite3, on vanila rails4-0 stable app https://gist.github.com/arthurnn/b6b2dc053786b32bf94a

cc @jduff @camilo review @byroot

[coveralls]

Coverage increased (+0.01%) when pulling 66448f4c2bcc4ab6e6e5a8dea7c4437661cf6522 on arthurnn:perf_regression_40 into 2bb3752ad90944324924d4054ea852c9d23be7cc on byroot:master.

[byroot]

Thanks!