Weird Deletion null error

Question

I'm trying to delete from a join table I made and I'm getting a weird error I cant figure out.

Here are my models

class ArticlesUser < ActiveRecord::Base
 # attr_accessible :title, :body
 belongs_to :user
 belongs_to :article
end

class Article < ActiveRecord::Base
 attr_accessible :title
 belongs_to :user

 has_many :articles_users
 has_many :likes, :through => :articles_users, :class_name => 'User', :source => :user    
end

class User < ActiveRecord::Base 
 has_many :articles, :order => 'id DESC'
 has_and_belongs_to_many :badges

 has_many :articles_users
 has_many :likes, :through => :articles_users, :class_name => 'Article', :source => :article
end

Testing in the Rails Console you can see the error:

> a = Article.find(13) 
> a.articles_users #works fine, returns an array of users who "like" the article
> a.articles_users.where(user_id: 3) #works as well
> a.articles_users.where(user_id: 3).first.destroy #this is where the error is thrown!

Here is there error:

 ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'articles_users.' in 'where clause': DELETE FROM `articles_users` WHERE `articles_users`.`` = NULL

Why does it seem to be completely ignoring the where hash? Please help me with this I've spent hours today trying to figure it out.

Thanks!

Edit:

The articles_users table has 2 columns: article_id and user_id

Edit:

This is copy and pasted from the console:

1.9.3p194 :004 > a.articles_users.where(user_id: 3).first
ArticlesUser Load (0.7ms)  SELECT `articles_users`.* FROM `articles_users` WHERE    `articles_users`.`article_id` = 13 AND `articles_users`.`user_id` = 3 LIMIT 1
=> #<ArticlesUser user_id: 3, article_id: 13> 

Answer 1

I tried and reproduced your issue.

From Your output it seems you don't have a id column in ArticlesUser which is the cause if issue.

=> #<ArticlesUser user_id: 3, article_id: 13> 

I tried adding id column to the table and it worked like charm. Created a new migration and add it

 add_column :articles_users, :id, :primary_key

When you destroy a record rails uses its id as a reference to delete it from database.

Check example.

 DELETE FROM `articles_users` WHERE `articles_users`.`id` = 1