Original blog post (January 3, 2011) http://vitobotta.com/serialisable-validatable-tableless-model/
Tableless Model
This is an extended Hash that has a defined collection of method-like attributes, and only these attributes can be set or read from the hash. Optionally, you can also set default values and enforce data types for these attributes.
Tableless Model behaves in a similar way to normal ActiveRecord models in that it also supports validations and can be useful, for example, to reduce database complexity in some cases, by removing associations and therefore tables.
In particular, by using Tableless Model, you could save tables whenever you have one to one associations between a parent model and a child model containing options, settings, debugging information or any other collection of attributes that belongs uniquely to a single parent object.
Removing database tables also means reducing the number of queries to fetch associations, therefore it can also help a little bit with performance.
Installation
Tableless Model is available as a Rubygem:
gem install tableless_model
Usage
For example's sake, say we have these two models:
class Page < ActiveRecord::Base
# having columns such as id, title, etc
has_one :seo_options
end
class SeoOptions < ActiveRecord::Base
set_table_name "seo_options"
# having columns such as id, title_tag, meta_description, meta_keywords,
# noindex, nofollow, noarchive, page_id
belongs_to :page
end
So that each instance of Page has its own SEO options, and these options/settings only belong to a page, so we have a one to one association, and our database will have the tables "pages", and "seo_options".
Using Tableless Model, we could remove the association and the table seo_options altogether, by storing those options in a column of the pages table, in a YAML-serialized form. So the models become:
class Page < ActiveRecord::Base
# having columns such as id, title, seo, etc
has_tableless :seo => SeoOptions
end
class SeoOptions < ActiveRecord::TablelessModel
attribute :title_tag, :type => :string, :default => "default title tag"
attribute :meta_description, :type => :string, :default => ""
attribute :meta_keywords, :type => :string, :default => ""
attribute :noindex, :type => :boolean, :default => false
attribute :nofollow, :type => :boolean, :default => false
attribute :noarchive, :type => :boolean, :default => false
end
That's it.
When you now create an instance of SeoOptions, you can get and set its attributes as you would do with a normal model:
seo_options = SeoOptions.new
=> <#SeoOptions meta_description="" meta_keywords="" noarchive=false nofollow=false noindex=false title_tag="default title tag">
seo_options.title_tag
=> "default title tag"
seo_options.title_tag = "new title tag"
=> "new title tag"
Note that inspect shows the properties of the Tableless Model in the same way it does for ActiveRecord models. Of course, you can also override the default values for the attributes when creating a new instance:
seo_options = SeoOptions.new( :title_tag => "a different title tag" )
=> <#SeoOptions meta_description="" meta_keywords="" noarchive=false nofollow=false noindex=false title_tag="a different title tag">
Now, if you have used the has_tabless macro in the parent class, Page, each instance of Page will store directly its YAML-serialized SEO settings in the column named "seo".
page = Page.new
page.seo
=> <#SeoOptions meta_description="" meta_keywords="" noarchive=false nofollow=false noindex=false title_tag="default title tag">
page.seo.title_tag = "changed title tag"
=> <#SeoOptions meta_description="" meta_keywords="" noarchive=false nofollow=false noindex=false title_tag="changed title tag">
And this is how the content of the serialized column would look like in the database if you saved the changes as in the example
--- !map:SeoOptions
noarchive: false
meta_description:
meta_keywords:
nofollow: false
title_tag: "changed title tag"
noindex: false
You can also pass a lambda/Proc when defining the default value of an attribute, so that the actual value will be calculated at runtime when a new instance of the tableless mode is being initialised:
class SeoOptions < ActiveRecord::TablelessModel
attribute :created_at, :type => :time, :default => lambda { Time.now }
end
Then, when the tableless model is initialised together with the parent model, the default value will be calculated and assigned in that moment:
>> SeoOptions.new
=> <#SeoOptions created_at_=Sun Jul 24 19:26:33 +0100 2011>
>> SeoOptions.new
=> <#SeoOptions created_at_=Sun Jul 24 19:26:37 +0100 2011>
>> SeoOptions.new
=> <#SeoOptions created_at_=Sun Jul 24 19:26:43 +0100 2011>
Of course, if a value is specified for an attribute when creating an instance of the tableless mode, the default value specified for that attribute will be ignored, including lambdas/procs:
>> SeoOptions.new :created_at => Time.local(2011, 7, 24, 18, 47, 0)
=> <#SeoOptions created_at=Sun Jul 24 18:47:00 +0100 2011>
For each of the attribute defined in the tableless model, shortcuts for both setter and getter are automatically defined in the parent model, unless the parent model already has a method of its own by the same name.
So, for instance, if you have the tableless model:
class SeoOptions < ActiveRecord::TablelessModel
attribute :title_tag, :type => :string, :default => "default title tag"
end
which is used by a parent model:
class Page < ActiveRecord::Base
has_tableless :seo => SeoOptions
end
you can get/set attributes of the tableless model directly from the parent model:
# this...
>> page.title_tag
=> "default title tag"
# is same as...
>> page.seo_options.title_tag
=> "default title tag"
For boolean attributes (or also truthy/falsy ones) you can also make calls to special getters ending with "?", so to get true or false in return, depending on the actual value of the attribute:
# this...
>> page.title_tag?
=> true
Encryption
If for some reason you'd like to encrypt the data serialised with the tableless model, so that it cannot be read in clear when looking directly at the contents of the database, you can enable encryption by simply specifying an encryption key:
class SomeModel < ActiveRecord::Base
has_tableless :seo => EncryptedTablelessModel, :encryption_key => "a398bbfaac38c79e60a6e398efba8571"
end
In the database, the encrypted tableless model will look similar to this:
Fxq8TU8syHgWBk1ndGt6U5pXZDbDVs3+lLFcxWkvc3b9OONp02RBf+vkmwl2O5VIZpPVqkMiM3Y3zsv5B2N9sXP1eb7Erskq5T3A3oclHoiXvvPizbKbe0T+pulUdbd+GWka8UYHT1FE/vRNAb6o+F83plL6m8ctWTWafM/skqzVXing1FBqpK0Iv+9H8cK3rOjdxdaWT4RMqvRG//MAsAl8gBor2dIdwbg2iap9j42JYSqua8RlGuPKzr/I4dwSYYO1ldg+gDYHRXLIJ//law==--ohQLUAuE4RU+btUyOibx7g==
Validations
Tableless Model uses the Validatable gem to support validations methods and callbacks (such as "after_validation"). Note: it currently uses the Rails 2.x syntax only.
Example:
class SeoOptions < ActiveRecord::TablelessModel
attribute :title_tag, :type => :string, :default => ""
attribute :meta_description, :type => :string, :default => ""
attribute :meta_keywords, :type => :string, :default => ""
attribute :noindex, :type => :boolean, :default => false
attribute :nofollow, :type => :boolean, :default => false
attribute :noarchive, :type => :boolean, :default => false
validates_presence_of :meta_keywords
end
Testing:
x = SeoOptionsSettings.new
=> <#SeoOptions meta_description="" meta_keywords="" noarchive=false nofollow=false noindex=false title_tag="">
x.valid?
=> false
x.meta_keywords = "test"
=> "test"
x.valid?
=> true
TODO
- Update validations syntax to that of Rails 3
- Support for associations
Authors
- Vito Botta ( http://vitobotta.com )
Contributing
- Fork the project on Github.
- Make your feature addition or bug fix.
- Add specs for it, making sure all specs green.
- Commit, and send me a pull request.
Compatibility
- Tested with REE/1.8.7, 1.9.2
Change log
26.07.2011
- Added support for encryption
24.07.2011
- Added support for passing Proc/lamba when defining the default attribute of a value
- Added shortcuts to call getters/setters of attributes defined in a tableless model, from its parent model directly
License
MIT License. Copyright 2010 Vito Botta. http://vitobotta.com