Data type of attribute on join model in Active Record/Rails 3.2/PostgreSQL database

Question

I have models Client and Sessions and a join model ClientSessionAssignment that associates the two. ClientSessionAssignment has one join column score which is defined as decimal type in schema.rb. I'm using has_many with select to preload score values when querying instances of Client as follows:

class Client < ActiveRecord::Base
  has_many :sessions,
    :through => :client_session_assignments,
    :select => 'sessions.*, client_session_assignments.score'
end

Despite score being defined as decimal in the database, when it is accessed this way, Active Record represents it as a string, i.e. Client.first.sessions.first.score.class yields String when I would expect it to yield BigDecimal. Consequently, I have to cast or convert scores obtained this way to BigDecimal before I can perform any calculations on them.

UPDATES

It turns out that only the postgresql database adapter exhibits this strange behaviour. I have filed https://github.com/rails/rails/issues/13044 to track this in the Rails bug tracker on GitHub: full test case is at https://gist.github.com/rcook/7670071.

What is the output when you remove the :select option in your association declaration and run Client.first.sessions.first.score.class again? — DiegoSalazar
– DiegoSalazar, Commented Nov 22, 2013 at 16:05
Without the :select option, then score is not added to Client.first.sessions.first. — Richard Cook
– Richard Cook, Commented Nov 23, 2013 at 16:52
Oh right. Try this instead: Client.first.client_session_assignments.first.score.class — DiegoSalazar
– DiegoSalazar, Commented Nov 23, 2013 at 18:52
What database you are using? and can you post the code in schema where decimal column is declared and can you post any sample app in github, because I tried with rails 3.2.13 and mysql db, its working fine(returns BigDecimal calling through associations) — nishanthan
– nishanthan, Commented Nov 24, 2013 at 17:29

DiegoSalazar · Accepted Answer · 2013-11-25 15:55:56Z

1

Seems like activerecord isn't type casting properly through the association. Try overwriting the accessor method in your join model:

class ClientSessionAssignment < ActiveRecord::Base
  def score
    ActiveRecord::ConnectionAdapters::Column.value_to_decimal super
  end
end

This should return a BigDecimal when you call Client.first.sessions.first.score

answered Nov 25, 2013 at 15:55

DiegoSalazar

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2 Comments

Richard Cook Over a year ago

I'll try that tonight. This looks like it'll work around this behaviour. Do you know if this is a bug in Active Record?

DiegoSalazar Over a year ago

Just found out from your question, it might be.

Richard Cook · Accepted Answer · 2013-12-01 22:16:02Z

0

This is a bug in Rails 3.2.x:

https://github.com/rails/rails/issues/13044

It's been fixed in Rails 4.0.1.

answered Dec 1, 2013 at 22:16

Richard Cook

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