Forum: Ruby Creating a ruby class with mass assignment

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Ruby N. (Guest)
on 2009-01-30 14:10
Hi,
How do I create a ruby class that has mass assignment functionality?  I
want it to work in a similar way to the way in which ActiveRecord does,
ie.
MyClass.new
=> #<MyClass:>
MyClass.new(:name => "Cool class")
=> #<MyClass: @name="s">
MyClass.new(:name => "Cool class", :other_attribute => "some other")
=> #<MyClass: @name="s", @other_attribute="some other">

I have found the following code snippit which works for the mass
assignment part but doesn't work if I initialize the class without any
arguments:

class MyClass
  attr_accessor :name
  attr_accessor :other_attribute

  def initialize(args)
    args.keys.each { |name| instance_variable_set "@" + name.to_s,
args[name] }
  end
end

MyClass.new
ArgumentError: wrong number of arguments (0 for 1)
        from (irb):19:in `initialize'
        from (irb):19:in `new'
        from (irb):19

What is the best way of achieving mass assignment whilst still allowing
to initialize without parameters?
Rupert V. (Guest)
on 2009-01-30 14:46
(Received via mailing list)
> What is the best way of achieving mass assignment whilst still allowing
> to initialize without parameters?

def initialize(args = {})
  args.keys.each { ....... }
end
Robert K. (Guest)
on 2009-01-30 15:36
(Received via mailing list)
2009/1/30 Ruby N.y <removed_email_address@domain.invalid>:
>
> args[name] }
> to initialize without parameters?
You can make your life considerably easier by using Struct:

irb(main):001:0> Test = Struct.new :foo, :bar, :baz do
irb(main):002:1*   def self.create(h = {})
irb(main):003:2>     new(*members.map {|m| h[m.to_sym]})
irb(main):004:2>   end
irb(main):005:1> end
=> Test
irb(main):006:0> Test.create(:foo => 1)
=> #<struct Test foo=1, bar=nil, baz=nil>
irb(main):007:0> Test.create(:bar => 3, :foo => 123)
=> #<struct Test foo=123, bar=3, baz=nil>

Kind regards

robert
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