如何在Rails中使用属于自己的模型进行查询

Question

I'm using Rails 3.2. I have a setup similar to the following:

class User < ActiveRecord::Base
  attr_accessible :is_admin
  belongs_to :created_by, :foreign_key => :created_by_id, :class_name => 'User'
end

This works if not using ActiveRecord query, just like the following:

#rails console
User.first.created_by.is_admin
#=> true

#But I want to query like the following, but it doesn't work
User.where(:created_by => {:is_admin => true})
#ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'created_by.is_admin' in 'where clause'...

#This also doesn't work:
User.joins(:created_by).where(:created_by => {:is_admin => true})
#ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'created_by.is_admin' in 'where clause'

I would really be grateful for any help.

Answer 1

You could do it using 2 queries

admin_ids = User.where(:is_admin => true).pluck(:id)
@users = User.where(:created_by_id => admin_ids)

I'd do this because

• A lot of times, 2 simple queries are faster than 1 complex join query
• Readable & easy to understand