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authorSean Griffin <sean@thoughtbot.com>2015-01-20 14:09:53 -0700
committerSean Griffin <sean@thoughtbot.com>2015-01-20 14:42:15 -0700
commitbe9b68038e83a617eb38c26147659162e4ac3d2c (patch)
tree49c393437f2d92da3f6cf6a1ef09ee7eb9b4b6ca /activerecord/lib/active_record/attribute_methods.rb
parent08fe700e2fd57a63d1ee899b63e0e818bc0f4e69 (diff)
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Introduce `ActiveRecord::Base#accessed_fields`
This method can be used to see all of the fields on a model which have been read. This can be useful during development mode to quickly find out which fields need to be selected. For performance critical pages, if you are not using all of the fields of a database, an easy performance win is only selecting the fields which you need. By calling this method at the end of a controller action, it's easy to determine which fields need to be selected. While writing this, I also noticed a place for an easy performance win internally which I had been wanting to introduce. You cannot mutate a field which you have not read. Therefore, we can skip the calculation of in place changes if we have never read from the field. This can significantly speed up methods like `#changed?` if any of the fields have an expensive mutable type (like `serialize`) ``` Calculating ------------------------------------- #changed? with serialized column (before) 391.000 i/100ms #changed? with serialized column (after) 1.514k i/100ms ------------------------------------------------- #changed? with serialized column (before) 4.243k (± 3.7%) i/s - 21.505k #changed? with serialized column (after) 16.789k (± 3.2%) i/s - 84.784k ```
Diffstat (limited to 'activerecord/lib/active_record/attribute_methods.rb')
-rw-r--r--activerecord/lib/active_record/attribute_methods.rb33
1 files changed, 33 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 8f165fb1dc..b2db0ceae7 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -369,6 +369,39 @@ module ActiveRecord
write_attribute(attr_name, value)
end
+ # Returns the name of all database fields which have been read from this
+ # model. This can be useful in devleopment mode to determine which fields
+ # need to be selected. For performance critical pages, selecting only the
+ # required fields can be an easy performance win (assuming you aren't using
+ # all of the fields on the model).
+ #
+ # For example:
+ #
+ # class PostsController < ActionController::Base
+ # after_action :print_accessed_fields, only: :index
+ #
+ # def index
+ # @posts = Post.all
+ # end
+ #
+ # private
+ #
+ # def print_accessed_fields
+ # p @posts.first.accessed_fields
+ # end
+ # end
+ #
+ # Which allows you to quickly change your code to:
+ #
+ # class PostsController < ActionController::Base
+ # def index
+ # @posts = Post.select(:id, :title, :author_id, :updated_at)
+ # end
+ # end
+ def accessed_fields
+ @attributes.accessed
+ end
+
protected
def clone_attribute_value(reader_method, attribute_name) # :nodoc: