Posts

What are delegate, delegate method, SimpleDelegator in ruby

 delegate methods in Rails, exposing only necessary methods of containing objects, thereby, making them more easily accessible. class Parent   def initialize     @child = Child.new   end end class Child   def initialize     @data = []   end   def insert(data)     @data << data   end   def fetch(key)     @data[key]   end end parent = Parent.new if you try this parent.insert("imrahul") then you will get response undefined method `insert' for #<Parent:0x000055f4915673a0 @child=#<Child:0x000055f491567350 @data=[]>> (NoMethodError)   This code will work if we overide methods of child class class Parent   def initialize     @child = Child.new   end   def insert(data)     @child.insert(data)   end   def fetch(index)     @child.fetch(index)   end end class Child   def initialize     @data = []   end   def insert(data)     @data << data   end   def fetch(key)     @data[key]   end end parent = Parent.new parent.insert("imrahul") So this is how dele

Completely uninstall elasticsearch in Linux

sudo apt-get remove elasticsearch sudo apt-get --purge autoremove elasticsearch sudo dpkg --remove elasticsearch sudo dpkg --purge elasticsearch sudo dpkg --purge --force-all elasticsearch sudo rm -rf /var/lib/elasticsearch/ sudo rm -rf /etc/elasticsearch If still facing any issues then you have to delete source file too. cd /etc/apt/sources.list.d/ sudo rm -rf elastic-*   Install Elasticsearch in ubuntu 20, 18, 16

Install Elastic search 5.x in ubuntu 20, 18, 16

Look for OpenJDK in APT sudo apt search openjdk Install OpenJDK 8 sudo apt-get install openjdk-8-jdk Add the proper GPG key for ElasticSearch wget -qO - https://artifacts.elastic.co/GPG-KEY-elasticsearch | sudo apt-key add - Make sure to install/update transport sudo apt-get install apt-transport-https Save the repo definition echo "deb https://artifacts.elastic.co/packages/5.x/apt stable main" | sudo tee -a /etc/apt/sources.list.d/elastic-5.x.list Update APT and install ElasticSearch from APT sudo apt-get update && sudo apt-get install elasticsearch Reload the daemon sudo /bin/systemctl daemon-reload Allow ElasticSearch to start on boot sudo /bin/systemctl enable elasticsearch.service Lets fire up ElasticSearch... sudo systemctl start elasticsearch.service Lets see if we have some logs sudo ls -la /var/log/elasticsearch/ Have a look at the logs and make sure that ElasticSearch has properly initiated sudo cat /var/log/elasticsearch/elasticsearch.

What is the Peatio cryptocurrency exchange or trading plateform?

  Cryptocurrency Exchange A cryptocurrency is nothing but a digital currency. Cryptocurrency exchanges are the platforms where you can buy, sell or exchange cryptocurrencies with other digital currency or with other assets such as fiat money. Fiat currency is like paper money for example Rupees, Dollars whose value is decided by the government. To start with the cryptocurrency exchange, you have to create an account in a cryptocurrency exchange. The exchange will then verify your account. When you want to buy the cryptocurrency, check the asks and when you want to sell the cryptocurrency, check the bids. The ask represents the lowest price sell order that is currently available in the market or the lowest price that someone is willing to go short. The bids represent the highest price buy order that is currently available in the market. Peatio Cryptocurrency Exchange Peatio is an open-source cryptocurrency exchange developed in Ruby On Rails framework. You can easily use the Peatio cryp

Transition Block in Rails with_lock

What is with_lock? how it work Ans:  If two users read a value from a record and then update it simultaneously, one of the values has to “win” and data integrity will be compromised. This is dangerous especially when dealing with money or inventory stocks. For example: User has a card balance = 10 User opens browser A and fill out 5 USD to buy User opens browser B and fill out 10 USD to buy User hits “Buy” button of both browsers at the same time Request A reads card balance=10 Request B reads card balance=10 Request A updates balance -= 5 (balance now is 10-5=5) Request B still has the instance card balance=10 (even though request A already decremented it) Request B updates balance -= 10 (balance now is 10-10=0) Final balance is now 0 User was able to purchase 15 USD when the initial balance was only 10 USD. This is race condition potentially at its worst case! Rails doesn’t do locking when loading a row from the database by default. If the same row of data from a table is loaded by t

Faraday::SSLError: SSL_connect returned=1 errno=0 state=error: certificate verify failed (certificate has expired)

  require 'openssl' OpenSSL::SSL::VERIFY_PEER = OpenSSL::SSL::VERIFY_NONE put this lines in config/application.rb

unterminated string meets end of file +rails

 This error is because you are trying to instert special symbol in record. User.last.update(password: "!@#$") User.last.update(password: "!@/#$") //it will not throw any errors.

The "chunk" argument must be of type string or an instance of Buffer or Uint8Array. Received an instance of Array

 res.end() to res.send()

Some Ruby on Rails interview questions

 1) How flash message work in ruby on rails? Ans. They are stored in your session store. The default since rails 2.0 is the cookie store, but check in config/initializers/session_store.rb to check if you're using something other than the default. According to APIdock : ActionController/Flash, it is stored in a session. Note that if sessions are disabled only flash.now will work. When using flash.now, your values are not available in the next request. 2) What is the use of Asset-PipeLine in Rails? Ans. Assets(css, scss, js, coffeescript, images etc), its fast executed in rails application because of asset pipeline when we compile it or when its compiled, it will generate a single source code file or a manifest file, so that's why assets are interpret fastly. 3)   Difference between find and find_by? Ans . The find method is usually used to retrieve a row by ID:            Model.find(1)           And it will throw ActiveRecord::RecordNotFound error if record not found. find_by is

Some important and unknown(least used) ruby methods.

 1) inject or reduce      When called, the inject method will pass each element and accumulate each sequentially.     ex:         [1,2,3].inject(:+)    => ((1+2)+3))   //we have can any operator here i.e +,-,*,/,%         OR         [1,2,3].inject{|sum, value| sum + value } => 1 iteration:  (1 + 2)                                                                                             =>  2 iteration: (3(1st iteration sum)+3)            we  can also pass it a default value or base value for the accumulator.     ex:          [1,2,3].inject(0, :+)    => (0+(1+2)+3)) //so here initial value for sum is 0.          We can also use inject menthods for building hash's from the array's     ex:           [[:book, "data structure"], [:price, "400rs"]].inject({}) do |result, element|               result[element.first] = element.last               result           end            #=> {:book=>"data structure", :price=>"400rs&qu