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Ruby On Rails Interview Questions and Answers

Ques 16. Explain a polymorphic association in Ruby on Rails.

Ans. 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

class Employee < ActiveRecord::Base
  has_many : pictures, as: : imageable

class Product < ActiveRecord::Base
  has_many : pictures, as: : imageable
  • 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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Ques 17. What is a Proc?
Ans. 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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Ques 18. What is a lambda?
Ans. Lambdas are very similar to procs in terms of functionality. However, they have a few key differences. Lambdas check the number of arguments passed and will return an error if you try to pass the wrong number (while procs set extra variables to nil). The other difference is that lambdas can handle a return function, whereas procs will return an error.
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Ques 19. What are the three levels of method access control for classes and what do they signify? What do they imply about the method?
  • Public, protected, and private.

  • Public methods can be called by all objects and subclasses of the class in which they are defined in.

  • Protected methods are only accessible to objects within the same class.

  • Private methods are only accessible within the same instance.

  • Be able to explain why this does (or doesn’t matter), and when you would want to set a method as private.
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Ques 20. Explain what functional testing is in Ruby on Rails.
Ans. Functional testing in Rails allows you to test the response of  various actions contained in a controller. Using the Rails default test library, mini test, functional tests use a collection of assert statements that will tell your testing library to expect a certain response based on a control request passed in (either a get, post, patch, put, head, delete request).
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