Initializing instance variables in Activerecord

Question

I’m having difficulty initializing instance variables in Rails, I need to use a variable in several methods, but this needs to be initialized beforehand, for example:

class Test < ActiveRecord::Base    
  @test = 1

  def testar
    @test+1
  end    
end

t = Test.new
t.testar

Generates the following error:

test.rb:4:in `testar': undefined method `+' for nil:NilClass (NoMethodError)
    from test.rb:9:in `<main>'

For @test has not been initialized, so I see that it does not work to perform this initialization in the class body, there is a more elegant way to do this than you use after_initialize? As in the example below:

  def after_initialize
    @test = 1
  end

Answer 1

As far as I know there is no other recommendable way, except by using the after_initialize.

The initialize original class may not be invoked in some cases by Activerecord, then. o after_initialize was created precisely to solve the boot problem.

There’s an argument about all this in this matter of the OS and in this article. See also the documentation explaining the after_initialize.

Answer 2

The way you did, assigning @test = 1 within the class, you are defining a class variable and not an instance variable.

To do what you want, you can use the operator ||=. If you use the variable in more than one location, I suggest accessing it through a reading method.

class Test < ActiveRecord::Base
  def test
    @test ||= 1
  end

  def testar
    test + 1
  end
end

t = Test.new
t.testar # => 2

The operator @test ||= 1 works as if it were @test = @test || 1. The first time you call the test method, the @test variable is nil, so it assigns 1 to @test (and returns this value). In the next calls, as @test is already defined, the method only returns the variable value.