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面试准备

Ruby On Rails 面试题与答案

问题 66. Describe the difference between class and instance variables?

Class variables are created with the prefix ‘@@’ and are shared by all objects in a class.
Instance variables are created with the prefix ‘@’ and belong to a single object within a class.

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问题 67. Example some of the looping structures available in Ruby?

For loop, While loop, Until Loop.

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问题 68. Explain the difference between a has_one and belongs_to association in Ruby on Rails.

has_one: Indicates a direct 1:1 relationship between objects where each instance of a model contains one instance of another model.
A product has_one provider, a customer has_one order.

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问题 69. Explain a polymorphic association in Ruby on Rails.

Polymorphic associations allow a model to belong to more than one other model through a single association.

class Picture < ActiveRecord::Base

belongs_to : imageable, polymorphic: true

end

class Employee < ActiveRecord::Base

has_many : pictures, as: : imageable

end

class Product < ActiveRecord::Base

has_many : pictures, as: : imageable

end

Here, the class Picture belongs_to both Employee and Product, but does so through a single association rather than through multiple.
Be sure to know an appropriate situation to create a polymorphic association, such as creating a comment model associated with multiple other models (articles, photos, etc.). The advantage of using polymorphism here is that it allows you to create a single comment model, rather than separate models for each one (PhotoComment model, ArticleComment model, etc.)

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问题 70. What is a Proc?

Procs, short for procedures, act similar to blocks, but can be saved as variables and reused. Think of them as blocks you can call over and over again on multiple arrays.

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