3.1.0 breaks with PostgreSQL tables that have json columns

[leklund]

Setup: vanilla Rails 4.0.4 app using PostgreSQL 9.3. The 3.1.0 release breaks when using tagged_with on a model that utilizes a json column.

The tagged_with method is calling .uniq on every request and that in turn generates a query with a distinct table.* which breaks with json columns. See this pull request for a possible solution: #496

migration:

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.text :title
      t.text :content
      t.json :options

      t.timestamps
    end
  end
end

the model

class Post < ActiveRecord::Base
  acts_as_taggable
end

the error in action:

> Post.create(title:'one', tag_list:'lorem')
> Post.create(title:'two', tag_list:'lorem,ipsum')
> Post.create(title:'three', tag_list:'ipsum,dolor')
> Post.tagged_with('lorem')
> ActsAsTaggableOn::Tag Load (0.8ms)  SELECT "tags".* FROM "tags" WHERE (LOWER(name) = LOWER('lorem'))
  Post Load (0.9ms)  SELECT DISTINCT "posts".* FROM "posts" JOIN taggings posts_taggings_861d63c ON posts_taggings_861d63c.taggable_id = "posts".id AND posts_taggings_861d63c.taggable_type = 'Post' AND posts_taggings_861d63c.tag_id = 1
PG::UndefinedFunction: ERROR:  could not identify an equality operator for type json
LINE 1: SELECT DISTINCT "posts".* FROM "posts" JOIN taggings posts_t...

[seuros]

this is related to #496 , we should merge this PR once the tests pass.