Automated way to select all columns of joined table in ActiveRecord?

Wondering with the upgrade to Arel, if ActiveRecord yet supports an automated way to select in the columns from joined tables, without having to explicitly list them in a select clause.

G开发者_如何学Civen I'm joining the users table to posts, Would like to be able to do something like this in a more succinct manner:

  scope :select_user,
    select("posts.*, " + User.columns.map{|c| 
      "users.#{c.name} user_#{c.name}"}.join(','))

So, I want to automatically select the fields from user so that I get say

Post.joins(:user).select_user.first.user_name

I think what you actually want here is to use includes if you want to access the association's attributes after the query is complete. So the same query would be

Post.includes(:user).first.user.name

This will result in two queries, one select * from users and one select * from posts where posts.user_id in (id1, id2, id3...) (assuming post belongs_to user) which may be a performance hit in a particular situation, but may be worth it from a syntax standpoint. In some cases it may even be faster Rails :include vs. :joins.

Arel will also intelligently use a join if you add a restriction operator to the query e.g. Post.includes(:user).where('users.name = "Bo Bob"') will do one query with a join and also enable you to use the associations on the resulting Post object.

If I understand your question correctly, you can do it with 'joins':

class Post < ActiveRecord::Base
  belongs_to :user

  scope :select_user, joins(:user).where('users.name = "Mary"')
  ...
end

or with a param:

class Post < ActiveRecord::Base
  belongs_to :user

  scope :select_user, lambda {|user_name|
    joins(:user).where('users.name = ?', user_name)
  }
  ...
end