24 questions that come up in Ruby on Rails technical interviews, each with the answer and an explanation of why it is right.
Test yourself — 90 question bankAnswer: Web application framework following MVC pattern
Ruby on Rails is a server-side web application framework written in Ruby. Follows MVC (Model-View-Controller) pattern. Emphasizes convention over configuration and DRY principles.
Answer: Extracts business logic into dedicated classes
Service objects encapsulate business logic. Keep controllers, models thin. app/services/. Single responsibility. call method convention. Better organization, testability.
Answer: Relationships between models: has_many, belongs_to, has_one
Associations define model relationships. has_many, belongs_to, has_one, has_and_belongs_to_many, has_many :through. Provide convenient methods. Define in model classes.
Answer: Defines one-to-one relationship from child side
belongs_to defines child side: class Post < ApplicationRecord; belongs_to :user; end. Expects user_id foreign key. Provides user method. Singular.
Answer: Model-View-Controller
MVC: Model (data/business logic), View (presentation), Controller (handles requests, coordinates). Separation of concerns. Core architectural pattern in Rails.
Answer: Handles complex forms with multiple models
Form objects handle complex forms. Coordinate multiple models. Include ActiveModel::Model. Validations, save logic. Keep controllers clean. Better than accepts_nested_attributes_for.
Answer: Encapsulates complex queries
Query objects extract complex queries. Keep models clean. Reusable, testable. app/queries/. Return ActiveRecord::Relation for chaining. Single responsibility.
Answer: Defines one-to-many relationship from parent side
has_many defines parent side: class User < ApplicationRecord; has_many :posts; end. Provides posts collection. Plural. Can add dependent options.
Answer: rails new app_name
Create app with rails new app_name. Options: --database=postgresql, --skip-test. Creates complete directory structure. Run bundle install automatically.
Answer: Many-to-many through join model
has_many :through creates many-to-many via join model. has_many :comments, through: :posts. More flexible than HABTM. Can add attributes to join.
Answer: Adds presentation logic without modifying model
Decorators add presentation logic. Use Draper gem. Keep models clean. Delegate to model. app/decorators/. Alternative to bloated helpers.
Answer: app/, config/, db/, public/, test/, lib/, etc.
Main directories: app/ (MVC code), config/ (configuration), db/ (database), public/ (static files), test/ or spec/ (tests). Convention over configuration.
Answer: Rails configured for API-only applications
API mode: rails new app --api. No views, assets. Lighter middleware. ApplicationController < ActionController::API. JSON responses. Use for backend APIs.
Answer: Ensure data integrity before saving to database
Validations ensure data integrity: validates :name, presence: true. Run before save. Prevent invalid data. Add errors to model. Display in views.
Answer: Represents data and business logic, inherits from ApplicationRecord
Model represents data/business logic. Inherits from ApplicationRecord (Active Record). Maps to database table. Handles validations, associations, queries.
Answer: presence, uniqueness, length, format, numericality
Common: presence (required), uniqueness, length, format (regex), numericality, inclusion, exclusion. Custom validators possible. Multiple per field.
Answer: Converting models to JSON/XML
Serialization converts to JSON/XML. Use ActiveModel::Serializers, fast_jsonapi, jbuilder. Control output shape. API responses. Versioning consideration.
Answer: Handles requests, coordinates models and views
Controller receives requests, interacts with models, renders views. Inherits from ApplicationController. Actions are public methods. RESTful by convention.
Answer: Query language for APIs, alternative to REST
GraphQL provides flexible API queries. Use graphql-ruby gem. Single endpoint. Clients request exactly needed data. Alternative to REST. More complex but powerful.
Answer: Methods triggered at lifecycle events
Callbacks run at specific points: before_save, after_create, before_validation. Define in models. Use for side effects, computed fields. Can skip with save(validate: false).
Answer: Presents data, typically HTML templates with embedded Ruby
Views render presentation. Typically ERB templates (.html.erb). Can access instance variables from controller. Layouts wrap views. Partials for reusable components.
Answer: rails generate model Name field:type
Generate model: rails generate model User name:string email:string. Creates model file, migration, test. Can use shorthand: rails g model. Specify field types.
Answer: Horizontal partitioning across databases
Sharding splits data across databases. Horizontal scaling. Rails 6+ multi-database support. Connect to multiple databases. Complex but enables scaling.
Answer: Named queries for reuse
Scopes are reusable queries: scope :published, -> { where(published: true) }. Chain scopes. Keep queries DRY. Use lambdas for arguments. Class methods alternative.
The full Ruby on Rails bank has 90 questions across 3 difficulty levels — timed, shuffled, and scored.
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