Ruby on Rails Interview Questions Experienced

ROR Interview Questions Experienced 

1. Difference between the map & each?
• The map will return the new array with modified values.
• Each will return the same array with an object.
2. Write the  program to sort the array in ruby without using the sort method?
• def ary_sort(list, new_array = nil)
  return new_array if list.size <= 0
  if new_array == nil
  min = list.min
  new_array = [] end
  ary_sort(list, new_array)
  new_array << min list.delete(min)
  end  
• ary_sort([1,6,5,3,8,24,18])
3. Write the   Program for array pass the arguments? 
1. Input will be a = [2,3,4] ,a.add_no(2)   ====> Output - [4,5,6]
• Array.class_eval do
  def add_no(n)
  self.map{|x| x+ n}
  end
  end
4. Difference between the find and find_by in rails?
• find_by() returns the nil if the record does not exist in the database
• find() returns the  ActiveRecord::RecordNotFound exception f the record does not exist in the database.
5. How do access the private method outside the class?
• class Koti
•  private 
•   def test_priv
•     puts "this is the private method"
•   end
• end
• Koti.new.instance_eval(:test_priv)
6. Given two arrays of integers nums and index. Your task is to create a target array under the following rules:
1. * Initially target array is empty.
2. * From left to right read nums[i] and index[i], insert at index index[i] the value nums[i] in target array.
3. * Repeat the previous step until there are no elements to read in nums and index.
4. Return the target array.
5. Example 1:
6. Input: nums = [0,1,2,3,4], index = [0,1,2,2,1]
7. Output: [0,4,1,3,2]
8. 
   
• Explanation:
• nums       index     target
• 0            0        [0]
• 1            1        [0,1]
• 2            2        [0,1,2]
• 3            2        [0,1,3,2]
• 4            1        [0,4,1,3,2]
• 
  
• 
  
• Example 2:
• Input: nums = [1,2,3,4,0], index = [0,1,2,3,0]
• Output: [0,1,2,3,4]
• Explanation:
• nums       index     target
• 1            0        [1]
• 2            1        [1,2]
• 3            2        [1,2,3]
• 4            3        [1,2,3,4]
• 0            0        [0,1,2,3,4]
7. What is the garbage collection?
• Garbage collection allows the removal of the pointer values that is left behind when the execution of the program ends. -It frees the programmer from tracking the object that is being created dynamically on runtime
• The Ruby garbage collector also allocates memory. It’s a complete memory management system.
8. What is the difference between the attr_accessor,attr_accesible?
1. attr_accessor -> attr_accessor is a Ruby method that makes a getter and a setter.
2. attr_accesible -> attr_accesible is Rails method that allows you to pass in values to a mass assignment: new(attrs) or update_attributes(attrs)
3. attr_accessor is ruby code and is used when you do not have a column in your database, but still want to show a field in your forms. The only way to allow this is to attr_accessor :fieldname
4. attr_accessor is getter, setter method. whereas attr_accessible is to say that particular attribute is accessible or not. we should use the Strong parameter instead of attr_accessible to protect from mass assignment.
5. attr_accessor example

• class Address
      attr_accessor :city  
      def initialize
          @city = ""
      end
  end

•  Address.new.city  = "Miryalaguda"

• class Person
    def name
      @name
    end
  
    def name=(str)
      @name = str
    end
  end
  
  person = Person.new
  person.name = 'kotesh'
  person.name # => "kotesh"

• class Person
    attr_accessor :name
  end

• person = Person.new
  person.name = "koti"
  person.name # => "koti"

9. Write the program for the below input
1. Write the program for the below input
• Input data is ===> array = [1, 2] snap = Snapshot.new(array) array[0] = 3; array = snap.restore() puts array print(array.join()) #It should log "1,2" array.push(4) array = snap.restore() print(array.join()) #It should log "1,2"
• Program is
• class Snapshot def initialize(inp) @start_val =[] inp.each{|x| @start_val << x} @start_val.freeze end def restore() new_strt_val = [] @start_val.each{|y| new_strt_val<< y } return new_strt_val end end 
10. What are the design patterns in ruby?
• Service Objects
  View Objects
  Query Objects
  Decorators
   Form Objects
  Value Objects
  Policy Objects 
11. Write the program for palindrome in ruby?
1. • a = "RKR"
     new_ar = []
     a.each_with_index do |i,index|
      new_ar << a[(a.length-1) - index]
     end
     if a == new_ar.join(",")
       puts "palindrome number"
     else
       puts "It's not palindrome number"
     end
12. How to pass the block in the method using ruby?
• def method1 puts yield end method1{"testing block with arguments"}
13. Difference between the proc & block?
• Blocks are used extensively in Ruby for passing bits of code to functions
•  Procs behave like blocks, but they can be stored in a variable.
• A block is a collection of code enclosed in a do/end statement or between braces

• def block_method
    puts "we are in the method"
  endblock_method { puts "The block is called"}
  O/p => we are in the method

14. Given array how many times "1" is repeated?
• /p => a = [1,0,1,1,1,1,0,1] O/p => 6 Solution: a.collect{|x|x if x == 1}.inject(:+) a.count(1) a.inject(:+).
15. What is the use of webpackers in rails?
• Webpacker is a gem that allows easy integration of JavaScript pre-processor and bundler with Rails. It provides various helpers and configuration options to use webpack easily with Rails

• <%= javascript_pack_tag 'application', 'data-turbolinks-track': 'reload' %>