ActiveRecord query on model methods

If I have the following code:

class User < ActiveRecord::Base
  has_many :problems

  attr_accessible :email, :password, :password_conf开发者_Python百科irmation, :remember_me, :first_name, :last_name, :location, :address

  attr_internal_accessor :user_address

  def user_address
    self.address
  end

end

class Problem < ActiveRecord::Base
  belongs_to :user

  validates_presence_of :user_id, :title, :description, :tags
  delegate :address, :to => :user, :prefix => true

end

When I try to do this in AR this is what the call looks like:

Problem Load (0.2ms)  SELECT "problems".* FROM "problems" ORDER BY problems.user_address asc LIMIT 20 OFFSET 0
SQLite3::SQLException: no such column: problems.user_address: SELECT  "problems".* FROM "problems" ORDER BY problems.user_address asc LIMIT 20 OFFSET 0
Completed 500 Internal Server Error in 173ms

It gives me an error that it is not a column which is true, however it generates data just like active record would.

How can I search the output if this function as if it was a native active record column?

The way i usually do this is by using the model you want to return.

So if its addresses you want, something like:

def user_address
  Address.joins(:users).where(:user_id => user.id)
end

This way you get an AR relation object back and you can chain them.

The method user_address is supposed to be used in the code (mostly views), not to be passed to AR.

AR would require things to be more understood by the DB.

To DB sort (order) using the User#address column:

#Rails 3
p = Problem.includes(:user).order("users.address ASC").first
p.user_address

#Rails 2
p = Problem.find(:first, :include => :user, :order => "users.address ASC")
p.user_address

It might also be wise to check if a user exist for a problem when

def user_address
  self.user.try(:address) #just in case a problem doesn't have an associated user
end