mirakui / activerecord-mysql-index-hint Goto Github PK

Hi there, we have been using your library for a while. Thanks for maintaining it!

Today I ran into a curious Rails bug rails/rails#24193 that stemmed from the way the hints are set. It's not specific to the hints, it has to do any queries that:

• Set from(...) to a string
• Use an eager_load(:some_association)
• Call .count (like most pagination libraries)

I'm pretty sure the problematic line is https://github.com/rails/rails/blob/4232f7ee427a510eb07e420f5883611bcb0abfae/activerecord/lib/active_record/relation/finder_methods.rb#L408 but we can avoid this by making this line truthy https://github.com/rails/rails/blob/4232f7ee427a510eb07e420f5883611bcb0abfae/activerecord/lib/active_record/relation/finder_methods.rb#L402

I came across another hinting library https://github.com/winebarrel/arel-mysql-index-hint but it is "sticky" in that once you set a hint for one query, all subsequent queries against the model will reuse that hint.

So I wanted to ping you before submitting a PR.

What I'm envisioning is something like this:

• We modify Arel::Table or create a subclass of Arel::Table that includes an index hint attribute
• We modify the Arel visitor to output the index (similar to https://github.com/winebarrel/arel-mysql-index-hint/blob/master/lib/arel-mysql-index-hint/arel-visitors-mysql.rb#L7)
• However where we deviate is in how we use this. The users of this library would still call the same method (Product.where(user_id: 1).force_index(:idx_user_id).first) but we would instantiate an Arel::Table instead of setting the string.

A rough sketch of the code would look like:

def from_with_index_hint(hint_type, *args)
  return self if args.blank?
  indexes = args.map {|index| connection.quote_column_name index }
  temporary_arel_table = arel_table.dup # this is part of ActiveRecord
  temporary_arel_table.index_hint = "#{hint_type} INDEX(#{indexes.join(', ')})"
  self.from(temporary_arel_table)
end

So we just set the from() to a different Arel::Table and the overrided visitor that we write would output the hint.

What are your thoughts on a change like that?

While taking a look at [Feature] Active Record: Add use_index I've found this gem.

I started testing it by running specs the current master branch and got this error likely due to bundler's feature.

https://travis-ci.org/yahonda/activerecord-mysql-index-hint/jobs/272447821

[!] There was an error parsing `4.1.gemfile`: You cannot specify the same gem twice coming from different sources.
You specified that activerecord-mysql-index-hint (>= 0) should come from source at `../` and source at `../`
. Bundler cannot continue.
 #  from /home/travis/build/yahonda/activerecord-mysql-index-hint/gemfiles/4.1.gemfile:9
 #  -------------------------------------------
 #  
 >  gemspec :path => "../"
 #

I've pushed reboot_ci_at_travis branch to resolve this error. My first target is to run specs at Travis CI and wanted to get some feedback if this approach is correct.

Thanks.

Please if you can add mysql as a dependency so user won't be able to install gem if he is not using mysql.

I want to call force index in a join as in:

• http://stackoverflow.com/questions/1272399/what-is-the-syntax-to-force-the-use-of-an-index-for-a-join-in-mysql