# ActiveRecord Associations (Ruby on Rails)

> has_many, belongs_to, has_one, has_and_belongs_to_many, polymorphic, dependent destroy

- 24 interview questions
- Mid-Level
- [Interview Questions: Ruby on Rails](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions.md)

## 1. Which association should be used in a Comment model to indicate that a comment must belong to an article?

**Answer**

The belongs_to association is used to define a relationship where a record belongs to another. In this case, a Comment belongs to an Article. By convention, this implies that the comments table contains an article_id column which is a foreign key to the articles table.

## 2. Which association should be used in an Article model to allow having multiple associated comments?

**Answer**

The has_many association defines a one-to-many relationship. An Article can have multiple Comments. This association is the mirror of belongs_to and does not store a foreign key in its own table, but expects the associated model (Comment) to have an article_id column.

## 3. Which association should be used for a user to have a single profile, where the profile contains the foreign key?

**Answer**

The has_one association defines a one-to-one relationship where the other model contains the foreign key. In the case User has_one :profile, the profiles table will contain a user_id column. This is the inverse of has_one/belongs_to depending on where the foreign key is located.

## 21 more questions available

- How to model a many-to-many relationship between Post and Tag with a join table containing additional attributes?
- What is the default behavior of the dependent: :destroy option on a has_many association?

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