Postgresql table values don't match Ruby on Rails Active Record query results

Question

I have a table named monthly_trips in Postgresql. There is a row with values id = 3 & al = 107.415. My problem is when I try to access the value of the "al" column in rails. Using the Rails Console with the code below I get the result of 6154.426156397738. I have no idea what is generating this larger number (57.295779513 times larger to be exact). Any help would be greatly appreciated! Let me know if you need more information.

trip = MonthlyTrip.find(3)
result = trip.al

monthly_trip.rb

class MonthlyTrip < ActiveRecord::Base
  attr_accessible :al, :month, :vehicle_id, :year
  belongs_to :vehicle
end

psql output (select id, al from monthly_trips where id = 3;)

 id |   al    
----+---------
  3 | 107.415
(1 row)

psql output (\d monthly_trips)

   Table "public.monthly_trips"
   Column   |            Type             |                         Modifiers                          
------------+-----------------------------+------------------------------------------------------------
 id         | integer                     | not null default nextval('monthly_trips_id_seq'::regclass)
 vehicle_id | integer                     | 
 year       | integer                     | 
 month      | integer                     | 
 al         | numeric(9,3)                | 
 ak         | numeric(9,3)                | 
 az         | numeric(9,3)                | 
 ar         | numeric(9,3)                | 
 ca         | numeric(9,3)                | 
 co         | numeric(9,3)                | 
 ct         | numeric(9,3)                | 
 de         | numeric(9,3)                | 
 fl         | numeric(9,3)                | 
 ga         | numeric(9,3)                | 
 hi         | numeric(9,3)                | 
 ida        | numeric(9,3)                | 
 il         | numeric(9,3)                | 
 ind        | numeric(9,3)                | 
 ia         | numeric(9,3)                | 
 ks         | numeric(9,3)                | 
 ky         | numeric(9,3)                | 
 la         | numeric(9,3)                | 
 me         | numeric(9,3)                | 
 md         | numeric(9,3)                | 
 ma         | numeric(9,3)                | 
 mi         | numeric(9,3)                | 
 mn         | numeric(9,3)                | 
 ms         | numeric(9,3)                | 
 mo         | numeric(9,3)                | 
 mt         | numeric(9,3)                | 
 ne         | numeric(9,3)                | 
 nv         | numeric(9,3)                | 
 nh         | numeric(9,3)                | 
 nj         | numeric(9,3)                | 
 nm         | numeric(9,3)                | 
 ny         | numeric(9,3)                | 
 nc         | numeric(9,3)                | 
 nd         | numeric(9,3)                | 
 oh         | numeric(9,3)                | 
 ok         | numeric(9,3)                | 
 ore        | numeric(9,3)                | 
 pa         | numeric(9,3)                | 
 ri         | numeric(9,3)                | 
 sc         | numeric(9,3)                | 
 sd         | numeric(9,3)                | 
 tn         | numeric(9,3)                | 
 tx         | numeric(9,3)                | 
 ut         | numeric(9,3)                | 
 vt         | numeric(9,3)                | 
 va         | numeric(9,3)                | 
 wa         | numeric(9,3)                | 
 wv         | numeric(9,3)                | 
 wi         | numeric(9,3)                | 
 wy         | numeric(9,3)                | 
 created_at | timestamp without time zone | not null
 updated_at | timestamp without time zone | not null
Indexes:
    "monthly_trips_pkey" PRIMARY KEY, btree (id)

Migration file

class CreateMonthlyTrips < ActiveRecord::Migration
  def change
    create_table :monthly_trips do |t|
      t.integer :vehicle_id
      t.integer :year
      t.integer :month
      t.decimal :al, precision: 9, scale: 3
      t.timestamps
    end
  end
end

pg_locks table

locktype | database | relation | virtualxid | virtualtransaction | pid | mode | granted

"relation" | 11955 | 11000 | blank | "8/18417" | 25475 | "AccessShareLock" | TRUE

"virtualxid" | blank | blank | "8/18417" | "8/18417" | 25475 | ExclusiveLock" | TRUE

@cdesrosiers al is declared as a decimal with precision: 9, scale: 3 in my migration. This translated into a numeric(9,3) in Postgresql. — Ferrari692
– Ferrari692, Commented Dec 10, 2012 at 4:58
When you read trip.al in the console, you should be getting a BigDecimal object (#<BigDecimal: ... >). What does that look like? — cdesrosiers
– cdesrosiers, Commented Dec 10, 2012 at 6:08
Which version of Rails and pg are you using? I checked a 3.2 app that has a numeric (AKA :decimal) column in the database and it gets pulled out as a BigDecimal. You're getting a Float for some reason and that's not right. — mu is too short
– mu is too short, Commented Dec 11, 2012 at 1:27
@muistooshort I tried a to_d conversion on the Float in that ruby file and I am generating the same wrong number before it is inserted to PG. It must be a problem with Rails using Ruby's to_d to convert the Float. Thanks for pointing me toward this! — Ferrari692
– Ferrari692, Commented Dec 12, 2012 at 21:34

AllenC · Accepted Answer · 2013-04-11 03:13:30Z

1

Your "trip" variable results for an array that's why it returns BigDecimal

You can use this kind of method:

1) Indicated the 1st value returned from ActiveRecord

trip = MonthlyTrip.find(3).first
result = trip.al

OR

2) Looping each element found in the database.

trip = MonthlyTrip.find(3) trip.each do |t| puts t.al end

answered Apr 11, 2013 at 3:13

AllenC

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