59 lines
1.3 KiB
Markdown
59 lines
1.3 KiB
Markdown
---
|
|
layout: post
|
|
title: "Mongoid: Use ObjectId as created_at"
|
|
date: 2013-08-23 07:34
|
|
comments: true
|
|
categories:
|
|
- mongodb
|
|
- rails
|
|
- mongoid
|
|
description: "Mongoid: Use ObjectId as created_at"
|
|
---
|
|
|
|
**Update: Nov 20 2014:** add setter
|
|
|
|
One great feature of Mongodb is, that the first bytes of each ObjectID contains the time, they were generated.
|
|
This can be exploited to mimic the well known `created_at` field in rails.
|
|
First put this file in your lib directory.
|
|
|
|
|
|
```ruby
|
|
#lib/mongoid/created.rb
|
|
module Mongoid
|
|
module CreatedAt
|
|
# Returns the creation time calculated from ObjectID
|
|
#
|
|
# @return [ Date ] the creation time
|
|
def created_at
|
|
id.generation_time
|
|
end
|
|
|
|
# Set generation time of ObjectId.
|
|
# Note: This will modify the ObjectId and
|
|
# is therefor only useful for not persisted documents
|
|
#
|
|
# @return [ BSON::ObjectId ] the generated object id
|
|
def created_at=(date)
|
|
self.id = BSON::ObjectId.from_time(date)
|
|
end
|
|
end
|
|
end
|
|
```
|
|
|
|
If you are still using mongoid 3 replace `BSON::ObjectId` with `Moped::BSON::ObjectId`.
|
|
|
|
Now you can include this module in every Model, where you need created at.
|
|
|
|
```ruby
|
|
#app/models/user.rb
|
|
class User
|
|
include Mongoid::Document
|
|
include Mongoid::CreatedAt
|
|
# ...
|
|
end
|
|
u = User.new(created_at: 1.hour.ago)
|
|
u.created_at
|
|
```
|
|
|
|
That's all easy enough, isn't it?
|