MongoDB + Ruby. How to access document properties?

Question

I want to try Mongo with Ruby. I connected, selected collection and I can query data from MongoDB.

irb(main):049:0> coll.find_one({:x=>4})
=> #<BSON::OrderedHash:0x3fdb33fdd59c {"_id"=>BSON::ObjectId('4f8ae4d7c0111ba6383cbe1b'), "x"=>4.0, "j"=>1.0}>

irb(main):048:0> coll.find_one({:x=>4}).to_a
=> [["_id", BSON::ObjectId('4f8ae4d7c0111ba6383cbe1b')], ["x", 4.0], ["j", 1.0]]

But how to access propeties, when I retrieve BSON hash? I need something like this:

data.x
=> 4

to_hash method gives me the same BSON::OrderedHash... :(

mu is too short · Accepted Answer · 2019-03-15 17:45:41Z

4

When you say coll.find_one({:x=>4}), you get a BSON::OrderedHash back that you access like a normal Hash:

h = coll.find_one(:x => 4)
puts h['x']
# 4 comes out unless you didn't find anything.

If you use a full find instead of find_one, you get a MongoDB::Cursor which is an Enumerable so you can iterate it like any other collection; the cursor will return BSON::OrderedHash instances as you iterate so you can do things like this:

cursor = coll.find(:thing => /stuff/)
cursor.each { |h| puts h['thing'] }
things = cursor.map { |h| h['thing'] }

If you wanted objects instead of Hashes then you'd have to wrap the MongoDB::Cursor and BSON::OrderedHash instances with object yourself (possibly via Struct).

edited Mar 15, 2019 at 17:45

answered Apr 15, 2012 at 16:39

mu is too short

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lmcanavals · Accepted Answer · 2013-01-24 16:36:00Z

0

Mongodb find_one method returns hash object, find method returns cursor object.

Cursor object can be iterated and then is possible to extract the answer in a normal hash.

require 'rubygems'
require 'mongo'
include Mongo

client = MongoClient.new('localhost', 27017)

db = client.db("mydb")
coll = db.collection("testCollection")

coll.insert({"name"=>"John","lastname"=>"Smith","phone"=>"12345678"})
coll.insert({"name"=>"Jane","lastname"=>"Fonda","phone"=>"87654321"})

cursor = coll.find({"phone"=>"87654321"})
answer = {}
cursor.map { |h| answer = h }
puts answer["name"]

edited Jan 24, 2013 at 16:36

lmcanavals

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answered Jan 24, 2013 at 16:14

Harmonix

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