Insert an array of Ruby objects in a Mongo database

Question

So, I'm using the Ruby MongoDB driver and I want to insert and object like this:

 db.insert_one({
  'game_id' => @token,
  'board' => {
    'tiles' => @board.tiles
  }
})

where @board is an instance of a Board class.

class Board
 attr_accessor :tiles
  def initialize()
    @tiles = [Tile.new, Tile.new]
  end
end

and Tile

class Tile
  def initialize()
    @x = 1, @y = 1
  end
  def to_json(options)
    {"x" => @x, "y" => @y}.to_json
  end
end

So at the end, 'tiles' field should look like this:

'tiles': [{x:1, y:1}, {x:1, y:1}]

I'm getting this error:

undefined method `bson_type' for #<Tile:0x007ff7148d2440>

The gems I'm using: 'sinatra', 'mongo (2.0.4)' and 'bson_ext' (all required using Bundler.require). Thanks!

The error is telling you that the driver doesn't know how to put a Tile instance into MongoDB, MongoDB doesn't know what to do with Tiles and no one will automatically call to_json for you. — mu is too short
– mu is too short, Commented Jun 11, 2015 at 2:25
I've tried calling to_json, but it inserts the content as a String (a json string), not as an Array. — Marcos
– Marcos, Commented Jun 11, 2015 at 8:00
to_json returns a string, as_json returns a Hash. Yes, the naming is a bit confusing. Sorry, that wasn't my clearest comment ever. — mu is too short
– mu is too short, Commented Jun 11, 2015 at 17:11

Rostyslav Diachok · Accepted Answer · 2015-06-11 11:49:25Z

2

You can simply transform @board.tiles from collection of Objects to collection of ruby Hashes:

class Tile
  def initialize()
    @x = 1, @y = 1
  end
  def raw_data
    {"x" => @x, "y" => @y}
  end
end

db.insert_one({
  'game_id' => @token,
  'board' => {
    'tiles' => @board.tiles.map(&:raw_data)
  }
})

For more complex thing I recommend you to use mongoid http://mongoid.org/en/mongoid/

edited Jun 11, 2015 at 11:49

answered Jun 11, 2015 at 0:18

Rostyslav Diachok

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2 Comments

Marcos Over a year ago

(I cannot prove the code right now) But that would insert a (json )string and not an array, right? I'm aware of Mongoid, I just thought my problem was easy enough to use the native driver :p Thanks!

Rostyslav Diachok Over a year ago

@enrmarc You are almost right. There was a problem in my solution. It was transforming tiles to array of strings. But now I modified it to return an array of hashes

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