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Asked: 2026-05-27T02:17:05+00:00

I have some code written in Ruby 1.9.2 patch level 136 and I’m have

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I have some code written in Ruby 1.9.2 patch level 136 and I’m have an issue where when I perform a find via the _id in the raw ruby mongo driver I get a nil when trying to use a value from a csv file. Here’s the code: 

require 'mongo'
require 'csv'
require 'bson'

# Games database
gamedb = Mongo::Connection.new("localhost", 27017).db("gamedb")
@games = gamedb.collection("games")

# Loop over CSV data.
CSV.foreach("/tmp/somedata.csv") do |row|

  puts row[0] # Puts the ObjectId

  @game = @games.find( { "_id" => row[0] } ).first  
  puts @game.inspect

end

The CSV file looks like this: 

_id,game_title,platform,upc_db_match,upc
4ecdacc339c7d7a2a6000002,TMNT,PSP,TMNT,085391157663
4ecdacc339c7d7a2a6000004,Super Mario Galaxy,Wii,Super Mario Galaxy,045496900434
4ecdacc339c7d7a2a6000005,Beowulf,PSP,Beowulf,097363473046

The first column is the objectId in Mongo that I already have. If I perform a local find from the mongo command line the values in the first column, I get the data I want. However, the code above returns nil on the @game.inspect call.

I’ve tried the following variations, which all produce nil: 

@game = @games.find( { "_id" => row[0].to_s } ).first
@game = @games.find( { "_id" => row[0].to_s.strip } ).first

I’ve even tried building the ObjectId with the BSON classes as such: 

@game = @games.find( { "_id" => BSON::ObjectId(row[0]) } ).first

or 

@game = @games.find( { "_id" => BSON::ObjectId("#{row[0]}") } ).first

Both of which output the following error: 

/Users/donnfelker/.rvm/gems/ruby-1.9.2-p136@upc-etl/gems/bson-1.4.0/lib/bson/types/object_id.rb:126:in `from_string': illegal ObjectId format: _id (BSON::InvalidObjectId)
    from /Users/donnfelker/.rvm/gems/ruby-1.9.2-p136@upc-etl/gems/bson-1.4.0/lib/bson/types/object_id.rb:26:in `ObjectId'
    from migrate_upc_from_csv.rb:14:in `block in <main>'
    from /Users/donnfelker/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/csv.rb:1768:in `each'
    from /Users/donnfelker/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/csv.rb:1202:in `block in foreach'
    from /Users/donnfelker/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/csv.rb:1340:in `open'
    from /Users/donnfelker/.rvm/rubies/ruby-1.9.2-p136/lib/ruby/1.9.1/csv.rb:1201:in `foreach'
    from migrate_upc_from_csv.rb:10:in `<main>'

The crazy thing is, if I manually create the BSON ObjectId by hand it works (as shown below): 

@game = @games.find( { "_id" => BSON::ObjectId("4ecdacc339c7d7a2a6000004") } ).first

When I run @game.inspect I get my data back, as I would expect. However, If I change this to use row[0], I get nil.

Why? What am I doing wrong?

System Details

$ gem list

*** LOCAL GEMS ***

bson (1.4.0)
bson_ext (1.4.0)
mongo (1.4.0)

RVM Version: rvm 1.6.9

Ruby Version: ruby 1.9.2p136 (2010-12-25 revision 30365) [x86_64-darwin10.6.0]

Mongo Version: 

[initandlisten] db version v1.8.2, pdfile version 4.5
[initandlisten] git version: 433bbaa14aaba6860da15bd4de8edf600f56501b

Again, why? What am I doing wrong here? Thanks!

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1 Answer

  1. Editorial Team

    The first row is not being read as a header, to do that pass in :headers => true like this:

    require 'csv'

# Loop over CSV data.
CSV.foreach("/tmp/somedata.csv", :headers => true) do |row|

  puts row[0] # Puts the ObjectId

end

    If you do not pass the :headers parameter in you can see the first row[0] object is the string “_id”:

    _id
4ecdacc339c7d7a2a6000002
4ecdacc339c7d7a2a6000004
4ecdacc339c7d7a2a6000005

    When you include it, you are golden:

    4ecdacc339c7d7a2a6000002
4ecdacc339c7d7a2a6000004
4ecdacc339c7d7a2a6000005
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