20+ Ruby on Rails Developer Interview Questions and Answers

Concerns in Ruby on Rails are used to group common functionality that can be shared across multiple models.

• Concerns help in keeping the code DRY (Don't Repeat Yourself) by extracting reusable code into separate modules.

• They are used to encapsulate shared methods, scopes, validations, callbacks, etc.

• Concerns are included in models using mixins, which allow the shared functionality to be easily added to multiple classes.

• For example, a 'Searchable' concern can be created to add ...read more

Query to fetch records by username and group by age

• Use WHERE clause to filter records by username

• Use GROUP BY clause to group records by age

• Example: SELECT * FROM table_name WHERE username = 'example_username' GROUP BY age

Optimizing the database involves indexing, query optimization, denormalization, and caching.

• Use indexing on frequently queried columns to improve search performance.

• Optimize queries by avoiding unnecessary joins and using efficient SQL queries.

• Consider denormalizing data to reduce the number of joins needed for queries.

• Implement caching mechanisms to store frequently accessed data in memory for faster retrieval.

Ruby's return keyword is different from Java in terms of behavior and syntax.

• In Ruby, the return keyword is optional and can be omitted.

• Ruby's return keyword can be used to explicitly return a value from a method.

• In Java, the return keyword is mandatory and must be used to return a value from a method.

• Java's return keyword cannot be used to return from a block or lambda expression.

Class methods are called on the class itself, while instance methods are called on instances of the class.

• Class methods are defined using 'self' keyword in the method name.

• Instance methods are defined without 'self' keyword in the method name.

• Class methods are used for operations that are not specific to any instance of the class.

• Instance methods are used for operations that are specific to individual instances of the class.

The docker ps command is used to list all the running containers on a Docker host.

• It provides information about the container ID, image used, command being run, status, ports, and names of the running containers.

• It helps in monitoring and managing the containers on a Docker host.

• The command can be used with various options to filter and format the output as per requirements.

• Example: 'docker ps -a' lists all containers, including the ones that are not running.

• Example: 'docker ...read more

1. Devise - authentication solution. 2. Paperclip - file attachment management. 3. Cancancan - authorization solution. 4. Sidekiq - background job processing. 5. RSpec - testing framework.

• Devise: A flexible authentication solution for Rails applications.

• Paperclip: A file attachment management library for ActiveRecord.

• Cancancan: An authorization solution that provides a simple way to define abilities.

• Sidekiq: A background job processing library that uses threads to handle mult...read more

extend adds class methods, prepend adds instance methods, include adds module methods

• extend adds methods to a class as class methods

• prepend adds methods to a class as instance methods

• include adds methods to a class as module methods

Concurrency in Rails allows multiple tasks to be executed simultaneously, improving performance and responsiveness.

• Concurrency in Rails is achieved through the use of background jobs and threads.

• It allows multiple requests to be processed at the same time, improving the overall performance of the application.

• Popular tools for implementing concurrency in Rails include Sidekiq, DelayedJob, and Active Job.

• Concurrency can help prevent bottlenecks and improve the responsiveness of...read more

Meta programming is writing code that writes code, allowing for dynamic generation and modification of classes and methods at runtime.

• Meta programming allows for creating methods and classes dynamically.

• It can be used for defining methods at runtime based on certain conditions.

• Examples include defining methods using define_method or dynamically creating classes using Class.new.

include is used to add instance methods to a class, while extend is used to add class methods to a class.

• include is used to mix in module methods as instance methods in a class.

• extend is used to mix in module methods as class methods in a class.

• Example: include ModuleName adds ModuleName's instance methods to the class, while extend ModuleName adds ModuleName's class methods to the class.

Mixins in Ruby are a way to add functionality to a class without inheritance.

• Mixins are modules that can be included in a class to extend its functionality.

• They allow for code reuse and help avoid duplication.

• Mixins are included using the 'include' keyword in Ruby.

Migrations in Rails are a way to manage database schema changes.

• Migrations are Ruby classes that help modify the database schema.

• They allow you to create, modify, or delete database tables, columns, and indexes.

• Migrations provide a version control system for the database schema.

• They ensure that all developers working on the project have the same database structure.

• Migrations can be easily rolled back if needed, making it easy to revert changes.

• They are executed using the 'rak...read more

Inheritance is a concept in object-oriented programming where a class inherits attributes and behaviors from another class.

• Allows for code reusability by creating a new class that is based on an existing class

• Child class can access all the attributes and methods of the parent class

• Helps in creating a hierarchy of classes with shared characteristics

Sorting numbers in Ruby using built-in methods

• Use the sort method to sort numbers in ascending order

• Use the sort method with a block to sort numbers in descending order

• Use the sort_by method to sort numbers based on a specific criteria

SQL commands are used to interact with databases and perform operations like querying, updating, and deleting data.

• SELECT: Retrieve data from a database

• INSERT: Add new data to a database

• UPDATE: Modify existing data in a database

• DELETE: Remove data from a database

• CREATE TABLE: Create a new table in a database

Sorting code in JavaScript involves using built-in methods like sort() or implementing custom sorting algorithms.

• Use the sort() method to sort arrays in JavaScript.

• Custom sorting can be implemented by providing a compare function to the sort() method.

• Examples: arr.sort(), arr.sort((a, b) => a - b)

Custom implementation of flatten method in Ruby

• Create a recursive function to iterate through the array elements

• Check if each element is an array or not, if it is an array then call the function recursively

• Concatenate the elements into a single array and return the result

MVC is a software design pattern that separates an application into three main components: Model, View, and Controller.

• Model represents the data and business logic of the application

• View is responsible for displaying the data to the user

• Controller acts as an intermediary between Model and View, handling user input and updating the Model accordingly