https://gitlab.com/bonusly/public/mongoid-falsehoods

Querying fields in Mongo for those with null values will often look like this:

db.users.find({ deleted_at: null })

This is inefficient, even if you've indexed users.deleted_at because Mongo has to look for both documents that have a null value in the deleted_at field and documents that do not have a deleted_at field set at all. If you look at the explain results, you'll see "stage": "FETCH" instead of "stage": "IDXSCAN", which is really what we want.

Mongoid does not support storing false instead of null for DateTime fields.

This gem convinces it to allow doing so.

I'd encourage you to do some baseline explain queries, look at the executionTimeMillis before the change. Then, add the Gem, migrate existing data, and see the difference. This is Mongo's estimation of how long it'll take to run the quey.

Here's an example:

# before
User.where(deleted_at: nil).explain['executionStats']['executionTimeMillis'] # 4197
# after
User.where(deleted_at: false).explain['executionStats']['executionTimeMillis'] #=> 3055

So by switching from null to false, we shaved off about a second from this query. The improvement will vary based on the number of documents. That's with around 790,000.

Hopefully Mongo will address this Jira ticket at some point and make this gem unnecessary.

Add this line to your application's Gemfile:

gem 'mongoid-falsehoods'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install mongoid-falsehoods

Turn code from this:

field :deleted_at, type: DateTime

index({ deleted_at: 1 }, background: true)

def self.not_deleted
  where(deleted_at: nil)
end

def active?
  deleted_at.nil?
end

to

field :deleted_at, type: DateTime, default: false

index({ deleted_at: 1 }, background: true)

def self.not_deleted
  where(deleted_at: false)
end

def active?
  !deleted_at
end

You'll also have to migrate existing data:

User.where(deleted_at: null).update_all(deleted_at: false)

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/bonusly/mongoid-falsehoods. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the Mongo::Falsehoods project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

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