= Introduction

This is a Ruby driver for the 10gen Mongo DB. For more information about
Mongo, see http://www.mongodb.org.

Note: this driver is still alpha quality. The API will change, as *may* the
data saved to the database (especially primary key values). Do *_not_* use
this for any production data yet.

Start by reading the XGen::Mongo::Driver::Mongo and XGen::Mongo::Driver::DB
documentation, then move on to XGen::Mongo::Driver::Collection and
XGen::Mongo::Driver::Cursor.

A quick code sample:

  require 'mongo'

  include XGen::Mongo::Driver

  db = Mongo.new('localhost').db('sample-db')
  coll = db.collection('test')

  coll.clear
  3.times { |i| coll.insert({'a' => i+1}) }
  puts "There are #{coll.count()} records. Here they are:"
  coll.find().each { |doc| puts doc.inspect }

= Installation

Install the "mongo" gem by typing

  $ gem sources -a http://gems.github.com
  $ sudo gem install mongodb-mongo-ruby-driver

The first line tells RubyGems to add the GitHub gem repository. You only need
to run this command once.

=== From the GitHub source

The source code is available at http://github.com/mongodb/mongo-ruby-driver.
You can either clone the git repository or download a tarball or zip file.
Once you have the source, you can use it from wherever you downloaded it or
you can install it as a gem from the source by typing

  $ rake gem:install


= Demo

You can see and run the examples if you've downloaded the source. Mongo must
be running, of course.

  $ ruby examples/simple.rb

See also the test code, especially tests/test_db_api.rb.


= Notes

== String Encoding

The BSON ("Binary JSON") format used to communicate with Mongo requires that
strings be UTF-8 (http://en.wikipedia.org/wiki/UTF-8).

Ruby 1.9 has built-in character encoding support. All strings sent to Mongo
and received from Mongo are converted to UTF-8 when necessary, and strings
read from Mongo will have their character encodings set to UTF-8.

When used with Ruby 1.8, the bytes in each string are written to and read from
Mongo as-is. If the string is ASCII all is well, because ASCII is a subset of
UTF-8. If the string is not ASCII then it may not be a well-formed UTF-8
string.

== The DB class

=== Primary Key Factories

A basic Mongo driver is not responsible for creating primary keys or knowing
how to interpret them. You can tell the Ruby Mongo driver how to create
primary keys by passing in the :pk option to the Mongo#db method.

  include XGen::Mongo::Driver
  db = Mongo.new.db('dbname', :pk => MyPKFactory.new)

A primary key factory object must respond to :create_pk, which should take a
hash and return a hash which merges the original hash with any primary key
fields the factory wishes to inject. NOTE: if the object already has a primary
key, the factory should not inject a new key; this means that the object is
being used in a repsert but it already exists. The idea here is that when ever
a record is inserted, the :pk object's +create_pk+ method will be called and
the new hash returned will be inserted.

Here is a sample primary key factory, taken from the tests:

  class TestPKFactory
    def create_pk(row)
      row['_id'] ||= XGen::Mongo::Driver::ObjectID.new
      row
    end
  end

A database's PK factory object may be set after you obtain it, but only once.
The only reason it is changeable is so that libraries such as MongoRecord that
use this driver can set the PK factory after obtaining the database but before
using it for the first time.

=== Strict mode

Each database has an optional strict mode. If strict mode is on, then asking
for a collection that does not exist will raise an error, as will asking to
create a collection that already exists. Note that both these operations are
completely harmless; strict mode is a programmer convenience only.

To turn on strict mode, either pass in :strict => true when obtaining a DB
object or call the :strict= method:

  db = XGen::Mongo::Driver::Mongo.new.db('dbname', :strict => true)
  # I'm feeling lax
  db.strict = false
  # No, I'm not!
  db.strict = true

The method DB#strict? returns the current value of that flag.


= Testing

If you have the source code, you can run the tests.

  $ rake test

The tests assume that the Mongo database is running on the default port.

The project mongo-qa (http://github.com/mongodb/mongo-qa) contains many more
Mongo driver tests that are language independent. To run thoses tests as part
of the "rake test" task, download the code "next to" this directory. So, after
installing the mongo-qa code you would have these two directories next to each
other:

  $ ls
  mongo-qa
  mongo-ruby-driver
  $ rake test

The tests run just fine if the mongo-qa directory is not there.

Additionally, the script bin/validate is used by the mongo-qa project's
validator script.


= Documentation

This documentation is available online at http://mongo.rubyforge.org. You can
generate the documentation if you have the source by typing

  $ rake rdoc

Then open the file html/index.html.


= Release Notes

See the git log comments.


= To Do

* Add group_by. Need to figure out how we are going to send functions. The
  current thinking is that Mongo will allow a subset of JavaScript (which we
  would have to send as a string), but this is still under discussion.

* Tests for update and repsert.

* Add a way to specify a collection of databases on startup (a simple array of
  IP address/port numbers, perhaps, or a hash or something). The driver would
  then find the master and, on each subsequent command, ask that machine if it
  is the master before proceeding.

* Introduce optional per-database and per-collection PKInjector.

* More tests.

== Optimizations

* Only update message sizes once, not after every write of a value. This will
  require an explicit call to update_message_length in each message subclass.

* ensure_index commands should be cached to prevent excessive communication
  with the database. (Or, the driver user should be informed that ensure_index
  is not a lightweight operation for the particular driver.)


= Credits

Adrian Madrid, aemadrid@gmail.com
* bin/mongo_console
* examples/benchmarks.rb
* examples/irb.rb
* Modifications to examples/simple.rb
* Found plenty of bugs and missing features.
* Ruby 1.9 support.
* Gem support.
* Many other code suggestions and improvements.


= License

Copyright (C) 2008-2009 10gen Inc.

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU Affero General Public License, version 3, as published by
the Free Software Foundation.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
details.

See http://www.gnu.org/licenses for a copy of the GNU Affero General Public
License.