Sam Pierson's Blog » ActiveRecord

How to stop ActiveRecord putting attribute name in validation message

sam — Wed, 02 Sep 2009 20:43:12 +0000

Use http://github.com/gumayunov/custom-err-msg/tree/master

Put a ^ at the start of the :message => option:

Non-base messages are prefixed with the attribute name as usual UNLESS they begin with '^'
 in which case the attribute name is omitted.

Switching an ActiveRecord instance between STI classes

sam — Fri, 28 Aug 2009 07:11:16 +0000

Sometimes you wish to convert one STI class to another, e.g. promote User to Administrator.

ActiveRecord::Base#becomes(Klass) returns an instance of the current record converted to the specified Klass, e.g.:

 
user = User.find_by_login("sam")
user.becomes(Administrator)

Note however that this does not change the type attribute of the instance, so you still have an additional step to do if you want this conversion to be permanent.

ActiveRecord performance: validation and associations

sam — Thu, 12 Mar 2009 07:07:03 +0000

If you have two models associated in some way, it is usual to add a validates_presence_of validator to ensure that the models are connected before saving. However, be aware that there are two ways of doing this with different performance ramifications:

class BlogEntry < ActiveRecord::Base
  belongs_to :blog
  validate_presence_of :blog
end

During validation, Validates_presence_of :blog causes ActiveRecord to call self#blog to see if it is nil. As this is the name of the association it will cause AR to retrieve the associated record from the DB before ascertaining if it is nil. E.g. with Rails 2.2.2:

>> e = BlogEntry.find(1)
  BlogEntry Load (0.3ms)   SELECT * FROM "blog_entries" WHERE ("blog_entries"."id" = 1)
=> #
>> e.valid?
  Blog Load (0.3ms)   SELECT * FROM "blogs" WHERE ("blogs"."id" = 1)
=> true

If you are confident of your database integrity, you can do validates_presence_of :blog_id instead. This will save you an SQL query. In a model that is saved frequently, this can be quite beneficial.

class BlogEntry < ActiveRecord::Base
  belongs_to :blog
  validate_presence_of :blog_id
end

ActiveRecord eager-loading thru multiple associations

sam — Fri, 10 Oct 2008 05:26:39 +0000

I just found out how to do something I have been wondering for a long time: :include syntax to eager-load through multiple associations. In the rdoc for class ActiveRecord::Associations::ClassMethods I discovered you can nest include statements in hashes as follows: If for example table_a has_many table_b and table_b has_many table_c and table_c has_many table_d:

Model.find :first, :include => { :table_a => { :table_b => { :table_c => :table_d } } }