Question

**UPDATE: I found this:

“Active Record expects intermediate join tables to be named with a concatenation of the tables it joins, in alphabetical order.”

Sigh…
**

I have 3 models: images, videos and keywords. Images and videos look basically the same and I’ve been trying to do everything the same for them with regards to keywords. But adding a keyword to an image works fine while adding a keyword to a video doesn’t.

keyword.rb

has_and_belongs_to_many :cases
has_and_belongs_to_many :images
has_and_belongs_to_many :videos

video.rb

has_and_belongs_to_many :keywords

image.rb

has_and_belongs_to_many :keywords

schema.rb

create_table "images_keywords", :id => false, :force => true do |t|
  t.integer  "image_id"
  t.integer  "keyword_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

create_table "videos_keywords", :id => false, :force => true do |t|
  t.integer  "video_id"
  t.integer  "keyword_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

This works:

images_controller.rb

@image.keywords << Keyword.new(:word => "test")

This:

videos_controller.rb

@video.keywords << Keyword.new(:word => "test")

Gives me this error:

ActiveRecord::StatementInvalid in VideosController#create

PGError: ERROR:  relation "keywords_videos" does not exist
LINE 4:              WHERE a.attrelid = '"keywords_videos"'::regclas...
                                    ^
:             SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc,      a.attnotnull
          FROM pg_attribute a LEFT JOIN pg_attrdef d
            ON a.attrelid = d.adrelid AND a.attnum = d.adnum
         WHERE a.attrelid = '"keywords_videos"'::regclass
           AND a.attnum > 0 AND NOT a.attisdropped
         ORDER BY a.attnum

When I check the console for adding a keyword to an image, it correctly looks for “images_keywords” Why does it look for “keywords_videos” for videos???

What is different about the two?

Answer 1

When using has_and_belongs_to_many, the name of the join table needs to have the related models listed in alphabetical order, ie: keywords_videos not videos_keywords.