Question

I am using the Mongo Ruby driver and have this block of Ruby code before and after line 171 in my code, which is apparently the source of the error below it (the query.each line is line 171):

    query = get_callback.call( "databases", id )
    if query.count > 0
      puts query.count.inspect + " results: " + query.inspect
      res = {}
      query.each do |result|
        puts result.inspect
      end
    else
      puts "No results" + res.inspect
      res = {}
    end

The error:

1 results: <Mongo::Cursor:0x3fc15642c154 namespace='myproj.databases' @selector={"_id"=>BSON::ObjectId('4fe120e4a2f9a386ed000001')} @cursor_id=>
TypeError - can't convert Mongo::Cursor into Integer:
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/bson-1.6.4/lib/bson/byte_buffer.rb:156:in `pack'
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/bson-1.6.4/lib/bson/byte_buffer.rb:156:in `put_int'
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/mongo-1.6.4/lib/mongo/cursor.rb:603:in `construct_query_message'
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/mongo-1.6.4/lib/mongo/cursor.rb:466:in `send_initial_query'
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/mongo-1.6.4/lib/mongo/cursor.rb:459:in `refresh'
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/mongo-1.6.4/lib/mongo/cursor.rb:128:in `next'
        /Users/myuser/.rvm/gems/ruby-1.9.3-p194/gems/mongo-1.6.4/lib/mongo/cursor.rb:291:in `each'
        /Users/myuser/Code/myproj/my_file.rb:171:in `block in initialize'

My query object: {"_id"=>BSON::ObjectId('4fe120e4a2f9a386ed000001')}

I have not the faintest idea what’s causing this. I’ve verified the object I’m finding exists and the query.count shows that there’s a result in my Mongo::Cursor.

I’ve not found any examples of the issue on Google and every Mongo/Ruby on the web I’ve found uses an each iterator just like I do. Anyone know what’s the cause of this error? I notice I also get it when trying to use to_a to cast the collection to a JSON-usable object.

---

For what it’s worth, here’s the relevant part of byte_buffer.rb is below. The line with << is line 156.

def put_int(i, offset=nil)
  @cursor = offset if offset
  if more?
    @str[@cursor, 4] = [i].pack(@int_pack_order)
  else
    ensure_length(@cursor)
    @str << [i].pack(@int_pack_order)
  end
  @cursor += 4
end

Answer 1

This happens when you pass nil to a Ruby Mongo driver limit() method.