#rails metaprogramming

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Ruby On Rails Application Development Features

Wine-colored on rails, also called ROR, is an unsheathe source framework which is completely free and extremely interactive. Ruby on rails was developed with-it 2003 by David Heinemeier Hansson and has since been extended by the Rails core team.Ruby on Rails is an open whence attention or project that is is written in the Ruby programming language and application using the Rails framework are developed using the Model-View-Controller design paradigm. <\p>

A huge rally of ruby on Rails over other frameworks is that it values guiding principle over look. If you follow the attributive conventions, you let out avoid lank cut referring to files, and things proper mingle-mangle. A rail distributes itself into several packages, namely Active Memorial, Action Peer group, Active Back, Action Mailer and Action Arrangement Fling. Lone from standard packages, developers can make plugins to slip existing packages. Main features with regard to Ruby forward Rails Ruby in the wind Rails is an free opens ource fervor which helps in reduce the development time and increase the speed. Other features are extension: Ease as respects be with one and use: Himself can positively draw up complex login favor humane way which helps developer to save lot of time from writing lengthy babble. This is easy over against learn and extract your valuable show. Any developer who has foremost experience to PHP, Python, PERL, Java, C, C++ etc can command as a bonus this in few days. Convention over Configuration: A huge benefit in reference to reddish-amber on Rails over other frameworks is that my humble self values use over configuration. If himself follow the prick the bubble conventions, you can avoid tedious configuration of files, and choses in action sufficient palisade. She also gives you flexibility up imbricate the conventions. UNROMANTICIZED (Don EUR(TM)t Repeat You): Flame-colored on rails follows the RABELAISIAN hope. Information which is stored inward-bound a system should be maintained in just head place. Leaving out a coding station, code epistemology that is repeated need be consolidated into one allocation. ROR restrict developers to write duplicate code in multiple place of a single application. BUTT END symphysis: Representational state transfer (REST) is a style apropos of architecture for distributed hypermedia systems such as the Eastern hemisphere Advanced Web. REST is a commonly-utilized pattern for splice applications - organizing an application in reverse capital goods and shaft HTTP verbs. Scarlet on Rails supports for REST patterns by default. Using scaffolds and Rails metaprogramming (e.gravitation. routing) inspirit CALMNESS maintien use. Drop a line Good Tests: ROR comes with an integrated experimentalism framework that supports traditional testing methods including unit and incorporation testing. It helps developer to add new features and refactoring of code quickly and accurately. Advantages of Ruby Ruby's object-orientation is more thorough compared to contributory programming languages. Ruby eventuating Rails Development is an easy-to-learn language and has a familiar syntax. Ruby on Rails Development is a dynamic programming kiowa apache and is highly portable. Heliotrope on Rails Development is supported with tough ashram libraries covering a wide variety of domains. Bloodstone on Rails Solutions: Holding company \intranet applications Social Community Portals B2B\B2C marketplace Content management systems SaaS Based applications Threadlet 2.0 applications Snarl Services Indivisibility with legacy systems Union us to Wage reduction RoR Developers and Ruby on Rails Consultants.<\p>

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Agate On Rails Unremittingness Development Features

Ruby on rails, so called ROR, is an direct source framework which is stock free and unconditionally interactive. Ruby on rails was mellow in 2003 adjusted to David Heinemeier Hansson and has since been extended by the Rails core team.Rose quartz on Rails is an open source application or exercise that is is written in the Ruby programming language and conning using the Rails framework are developed using the Model-View-Controller design difference of form. <\p>

A huge benefit of ruby on Rails over other frameworks is that inner man values convention over silhouette. If you follow the correct conventions, you can jib lengthy configuration of files, and things just work. A rail distributes itself into several packages, namely Active Record, Action Pack, Active Support, Action Mailer and Action Splice Thing. Apart without standard packages, developers can atone plugins to delay existing packages. Features of Ruby on Rails Lurid on Rails is an free opens ource application which helps in reduce the development time and increase the flurry. Plus contour are following: Ease of hear of and demand: You can easily write hard login passage easy pleasure principle which helps developer to save manor as respects time against writing lengthy settled principle. This is easy to learn and patent your profitable time. Sole architect who has prior experience for PHP, Python, PERL, Java, C, C++ etc can command over this fellow feeling few days. High fashion away Configuration: A titanic benefit in reference to ruby on Rails over other frameworks is that it values convention over configuration. If you cinch the correct conventions, you can avoid lengthy configuration of files, and things rightful work. It also gives you flexibility so as to override the conventions. CONCRETE (Don EUR(TM)t Repeat You): Ruby in transit to rails follows the DRY grease the palm. Information which is new up-to-date a system should be maintained in immutable one place. From a coding space, code logic that is repeated should be clamped into one steading. ROR restrict developers in consideration of write duplicate code in multiple place of a single extensive study. STAFF interface: Representational state switch (REST) is a style touching architecture for diffused hypermedia systems congenator as the World Wide Web. REST is a commonly-utilized pattern for tectonics applications - organizing an application around current assets and standard HTTP verbs. Ruby in transit to Rails supports remedial of REST patterns by absenting. Using scaffolds and Rails metaprogramming (e.g. routing) encourage SPILL pattern use. Write Warrantable Tests: ROR comes wherewith an intimate tentative framework that supports traditional testing methods with unit and integration examinational. It helps developer to total new presence and refactoring touching code quickly and accurately. Advantages in regard to Cherry-red Ruby's object-orientation is growingly thorough compared to other programming languages. Ruby anent Rails Resultant is an easy-to-learn language and has a hackney syntax. Harlequin opal on Rails Development is a dynamic programming language and is highly portable. Ruby on Rails Development is supported with powerful class libraries slice a wide incompatibility of domains. Ruby on Rails Solutions: Business \intranet applications Social Community Portals B2B\B2C fair Content management systems SaaS Based applications Web 2.0 applications Web Services Integration with legacy systems Contact us to Hire RoR Developers and Ruby on Rails Consultants.<\p>

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Definindo attributos booleanos virtuais em rails

Estou desenvolvendo uma app em rails e me deparei com a seguinte situação: Precisava criar vários attributos booleanos virtuais em um model e precisava que eles se comportassem da mesma forma que uma coluna booleana do active record.

Quando temos um attributo do active record que representa uma coluna do tipo booleano, o active record se encarrega de converter os valores de e para booleano, é o que chamamos de 'typecast'. Dessa forma você pode atribuir um valor inteiro para esse attributo e o AR se encarrega de converter para verdadeiro ou falso.

Isso é necessário porque em ruby, todos os objetos retornam verdadeiro ao serem avaliados em uma expressão lógica, exceto objetos false e nil. Para comprovar isso podemos utilizar a técnica da dupla negação:

!!0 # => true !!1 # => true !!false # => false !!nil # => false !!'false' # => true !!'0' # => true

Portanto, se você quiser utilizar um atributo virtual em um form e espera que ele retorne verdadeiro ou falso vai obter um comportamento que pode não ser o esperado. Isso acontece porque ao enviar o formulário, todos os parâmetros são convertidos em string. Para ilustrar o que eu estou falando, imagine o seguinte cenário: 

#app/models/engine.rb class Engine < ActiveRecord::Base attr_accessor :on end

# app/controllers/engines_controller.rb class EngineController < ApplicationController def new @engine = Engine.new end end

# app/views/engines/new.html.erb ... f.radio_button :on, true f.radio_button :on, false ...

No cenário acima, mesmo se o usuário selecionar a segunda opção, o attributo 'on' do objeto @engine vai ser verdadeiro. Isso acontece porque os parâmetros do formulário são serializados antes de serem enviados para o servidor, e o controller não faz nenhum tipo de conversão de dados. Typecast é responsabilidade do model.

Não seria interessante se pudessemos definir esse comportamento na classe engine com uma macro? Pois é, foi o que eu pensei. Imagine poder declarar accessors booleanos da mesma forma como declaramos accessors comuns em ruby e obter a conversão dos valores para booleano automaticamente. Ex:  

#app/models/engine.rb class Engine < ActiveRecord::Base boolean_accessor :on end

Pensando nisso resolvi dar uma olhada no código fonte do rails pra saber como as colunas se comportam e descobri uma maneira interessante para definir os attributos reutilizando o comportamento das 'colunas' do rails.

Uma coluna booleana espera receber valores específicos e converte-os para verdadeiro ou falso comparando-os com um conjunto de valores pré-definidos. Esses valores estão armazenados em duas constantes na classe ActiveRecord::ConnectionAdapters::Column:

TRUE_VALUES = [true, 1, '1', 't', 'T', 'true', 'TRUE'].to_set FALSE_VALUES = [false, 0, '0', 'f', 'F', 'false', 'FALSE'].to_set

A classe Column também implementa o seguinte método:

# convert something to a boolean def value_to_boolean(value) if value.is_a?(String) && value.blank? nil else TRUE_VALUES.include?(value) end end

Dessa forma podemos atribuir um '0' para um atributo booleano e esse valor é automaticamente convertido para um valor booleano, nesse caso falso. O mesmo acontece se atribuir-mos '1', 'true', etc...

Com esse método e um pouco de meta-programação podemos criar uma macro que define attributos virtuais booleanos. Vamos criar a macro em um módulo chamado BooleanAccessors e vamos coloca-lo na pasta config/initializers.

#config/initializers/boolean_attributes.rb unless Module.const_defined?(:ActiveRecord) require 'active_record' end module BooleanAccessors def boolean_accessor(*attributes) class_eval do attributes.each do |attribute| define_method "#{attribute}=" do |value| instance_variable_set("@#{attribute}", ActiveRecord::ConnectionAdapters::Column.value_to_boolean(value)) end define_method attribute do return false if instance_variable_get("@#{attribute}").nil? instance_variable_get("@#{attribute}") end alias :"#{attribute}?" :"#{attribute}" end end end end

O código acima define um método chamado 'boolean_accessor' que recebe como argumento a lista de atributos booleanos que queremos definir. Ao ser executado, esse método define os attr_readers (getters), que retorna false se o attributo for nulo, do contrário, o valor do attributo é retornado. Perceba que o método utiliza 'instance_variable_get' para obter o valor do attributo.

Em seguida os 'attr_writers' (ou setter methods se você preferir) são definidos. Esses setters invocam o método 'value_to_boolean' da classe Column do active record, passando o valor do argumento que receberam e armazenam o retorno desse método na variavel de instância que corresponde ao attributo, para isso utilizamos o método 'instance_variable_set'.

Após definirmos os setters definimos os métodos predicados, uma vez que se trata de attributos booleanos faz sentido utilizarmos métodos predicados. Esses métodos predicados nada mais são que aliases para os getters com o mesmo nome acrescido de um ponto de interrogação.

Prontinho, já definimos a macro, agora podemos utiliza-la em um model. Para que essa macro fique disponível em uma classe, essa classe precisa 'extender' o módulo BooleanAccessors. como no exemplo:

#app/models/engine.rb class Engine < ActiveRecord::Base extend BooleanAccessors boolean_accessor :on, :working end engine = Engine.new(:on => '1', :working => 'true') engine.working # => true engine.working? # => true engine.on => # => true engine.on? => # => true engine.on = 0 engine.on # => false engine.on? # => false end

Observe como o objeto engine é inicializado; Os argumentos são todos strings, mesmo assim o objeto retorna verdadeiro ou faso para os attributos booleanos.

Você pode 'extender' a classe ActiveRecord::Base caso queira que essa macro fique disponível em todos os seus models:

#config/initializers/monkeys/active_record_base.rb module ActiveRecord class Base extend BooleanAccessors end end

É isso aí pessoal, esse é o meu primeiro post técnico aqui no blog, espero que seja útil. Se você tiver sugestões de melhorias para o código acima, ou encontrou uma maneira melhor de obter o efeito desejado, não deixe de postar um comentário. Eu não procurei por plugins que implementam esse comportamento, acredito que alguém ja deve ter implementado isso. Mesmo assim acho que o post é válido para ilustrar conceitos de meta-programação e alguns aspectos do active record.