不能访问的ActiveRecord增变器中的块 [英] can't access ActiveRecord mutators in a block

问题描述

我是个Rails的控制器中，我试图访问我的实例变量在一个块： 这给出了一个错误，说没有办法字段1的无：

I am inside a Rails controller and I am trying to access my instance variable in a block: This gives an error saying that "no method field1 for Nil":

Prawn::Document.generate("hello.pdf") do
  @model.field1
end

不过，如果我这样做，那么它的工作原理：

However, if I do this, then it works:

my_model = @model
Prawn::Document.generate("hello.pdf") do
  my_model.field1
end

难道这有什么做的ActiveRecord的块访问或实例变量？

Could this have something to do with ActiveRecord accessors or instance variables in a block?

推荐答案

这是怎么回事，因为内部的块code在对虾:: Document对象的上下文中执行。让我们去这里面code：

That's happening because code inside block is executed in context of Prawn::Document object. Let's go inside this code:

module Prawn
  class Document
    def self.generate(filename,options={},&block)
      pdf = new(options,&block)
      pdf.render_file(filename)
    end

    def initialize(options={},&block)
      if block
        block.arity < 1 ? instance_eval(&block) : block[self]
      end
    end
  end
end

正如你所看到的，块与执行文件对象自。它试图找到@model为自实例变量，不能做到这一点，并返回零。如果使用本地变量模式，你得到倒闭的帮助和code正常工作

As you can see, block is executed with Document object as self. It try to find @model as instance variable of self, can't do this and return nil. If you use local variable model, you get help of closures and your code is working properly

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