3.x fix for MySQL adapter to prevent MySQL 'LIMIT & IN/ALL/ANY/SOME subquery'" error

[dannguyen]

In regards to bug report 450:
#450

This pull contains a fix for a MySQL error generated by a combination of limit,tag_counts, andsum`

ActiveRecord::StatementInvalid: Mysql2::Error: This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery':

TaggableModel.new(:name => "Barb Jones").tap{|t| t.tag_list = ['awesome', 'fun'] }.save
TaggableModel.new(:name => "John Doe").tap{|t| t.tag_list = ['cool', 'fun', 'hella'] }.save
TaggableModel.new(:name => "Jo Doe").tap{|t| t.tag_list = ['curious', 'young', 'naive', 'sharp'] }.save
TaggableModel.all.each{|t| t.save }

expect( TaggableModel.limit(2).tag_counts.sum('tags_count') ).to eq 5

In other words, limit the model to the first 2 records, find tag counts for the 2 records, then sum those tag counts

MySQL generated 2.x

SELECT tags.*, taggings.tags_count AS count FROM "tags" JOIN (SELECT taggings.tag_id, COUNT(taggings.tag_id) 
  AS tags_count FROM "taggings" 
  INNER JOIN taggable_models ON taggable_models.id = taggings.taggable_id 
  WHERE (taggings.taggable_type = 'TaggableModel' 
    AND taggings.context = 'tags') 
    AND (taggings.taggable_id 

  IN(10,11)) 

  GROUP BY taggings.tag_id HAVING COUNT(taggings.tag_id) > 0) 
  AS taggings ON taggings.tag_id = tags.id

MySQL generated in 3.x

re: ActiveRecord::StatementInvalid: Mysql2::Error: This version of
MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery':

SELECT tags.*, taggings.tags_count AS count FROM `tags` JOIN (SELECT taggings.tag_id, COUNT(taggings.tag_id) 
  AS tags_count FROM `taggings` 
    INNER JOIN taggable_models ON taggable_models.id = taggings.taggable_id 
    WHERE (taggings.taggable_type = 'TaggableModel' 
      AND taggings.context = 'tags') 
      AND (taggings.taggable_id 


    IN(SELECT  taggable_models.id FROM `taggable_models`  LIMIT 2)) 

    GROUP BY taggings.tag_id HAVING COUNT(taggings.tag_id) > 0) 
    AS taggings ON taggings.tag_id = tags.id

Solution: Add a ActsAsTaggableOn::Tag.using_mysql? method and then revert to the 2.x way of
doing a group count in .all_tags and .all_tags_count

Also, collection.rb now has a private class method to switch between the 2.x and 3.x code. I've tentatively referred to it as .generate_tagging_scope_in_clause until a better patch is put in place. I say "better" as in, this patch fixes the broken behavior and passes all the specs, but if there were performance reasons for the breaking behavior, this patch reverts that as it basically does the counting query for Mysql as it did back in acts-as-taggable 2.x

[bf4]

If you could use this in Tag, that would be great https://github.com/mbleigh/acts-as-taggable-on/blob/master/lib/acts_as_taggable_on/tag.rb#L110

Any reason you didn't match case insensitive or some other way?

[bf4]

bump

[dannguyen]

Er yeah...no reason for my specific implementation, just general ignorance of what enumerated strings ActiveRecord might allow for adapter_name :)

Let me make sure I understand what you want before I submit the pull request. Basically,just wrap binary?

def using_mysql?
     !binary.nil?
end

[seuros]

Can you rebase ?