How do I update a cumulative field in a Rails database (using ActiveRecord or Mongoid)?

Posted by picardo on Stack Overflow See other posts from Stack Overflow or by picardo
Published on 2010-12-30T07:50:30Z Indexed on 2010/12/30 7:54 UTC
Read the original article Hit count: 209

Filed under:

activerecord

|

ruby-on-rails3

|

database-queries

|

mongoid

I want to update a field in a database table that has to have a cumulative value. So basically I need to find the current value of the field and update it using a new number.

My first inefficient try at this (in Mongoid) is:

v = Landlord.where(:name=>"Lorem")
v.update_attributes(:violations=>v.violations + 10)

Is there a simple method than making one query to read, then sum up, and another query to write?

© Stack Overflow or respective owner

Related posts about activerecord

Rails & ActiveRecord: Appending methods to models that inherit from ActiveRecord::Base

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a standard ActiveRecord model with the following: class MyModel < ActiveRecord::Base custom_method :first_field, :second_field end At the moment, that custom_method is picked up by a module sent to ActiveRecord::Base. The functionality basically works, but of course, it attaches itself… >>> More
Rails ActiveRecord - Best way to perform an include?

as seen on Stack Overflow - Search for 'Stack Overflow'
I have three models: class Book < ActiveRecord::Base has_many :collections has_many :users, :through => :collections end class User < ActiveRecord::Base has_many :collections has_many :books, :through => :collections end class Collection < ActiveRecord::Base belongs_to… >>> More
Getting types of the attributes in an ActiveRecord object

as seen on Stack Overflow - Search for 'Stack Overflow'
I would like to know if it is possible to get the types (as known by AR - eg in the migration script and database) programmatically (I know the data exists in there somewhere). For example, I can deal with all the attribute names: ar.attribute_names.each { |name| puts name } .attributes just… >>> More
Changing ActiveRecord attribute value in before_save hook

as seen on Stack Overflow - Search for 'Stack Overflow'
I needed to fix the encoding of an ActiveRecord attribute and decided to do it in a before_save hook. And at this point I noticed an unexpected feature. When I wanted to change the value of the attribute, simple using the attribute_name=XY did not work as I expected. Instead of that I needed to use… >>> More
Conditions with whitespaces in activerecord find

as seen on Stack Overflow - Search for 'Stack Overflow'
So i am trying to do this Order.find :all, :conditions => "org = 'test org'" what ends up firing is SELECT * FROM `orders` WHERE (org = 'test org') the whitespace in the argument gets stripped. what am i missing.. im really stumped here. please help! >>> More

Related posts about ruby-on-rails3

ruby-on-rails3, and select distinct using activereccord3

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, Some methods have been deprecated with Rails3. It is the case in particular with the following call ! Error.find(:all, :select => 'DISTINCT type') Is anybody have an idea, how to convert this call to an ActiveRecord3 valid statement ? I found nothing on the web ... Thanks >>> More
Rails3 server and bundler error: uninitialized constant Bundler (NameError)

as seen on Stack Overflow - Search for 'Stack Overflow'
I just install rails 3 and all gems that it need, but when I try to start server, it says about problem in boot script. [rap-kasta@acerAspire testR3]$ script/rails server /home/rap-kasta/tmp/testR3/config/boot.rb:7:in `rescue in <top (required)>': uninitialized constant Bundler (NameError)… >>> More
How to set ActiveModel::Base.include_root_in_json to false?

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm using Rails 3 w/ Mongoid, (so no ActiveRecord). Mongoid uses ActiveModel's "to_json" method, and by default that method includes the root object in the JSON (which I don't want). I've tried putting this in an initializer: ActiveModel::Base.include_root_in_json = false But get the error uninitialized… >>> More
No such file to load bundler error for Rails 3

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a Rails 3 app ready for staging. I haven't got a VPS host set up yet. As I was planning to have everything on shared host for the first few months. Problem: cd myapp bundle check result: The Gemfile's dependencies are satisfied Passenger error: Error message: no such file to load… >>> More
How to test Rails 3 Engines with Cucumber & Rspec?

as seen on Stack Overflow - Search for 'Stack Overflow'
I apologize if this question is slightly subjective... I am trying to figure out the best way to test Rails 3 Engines with Cucumber & Rspec. In order to test the engine a rails 3 app is necessary. Here is what I am currently doing: Add a rails test app to the root of the gem (myengine) by… >>> More