# GraphQL with Rails (Ruby on Rails)

> graphql-ruby gem, types, queries, mutations, resolvers, N+1 queries, batching

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

## 1. Which gem is most commonly used to implement GraphQL in a Rails application?

**Answer**

The graphql-ruby gem (often called simply graphql) is the reference solution for implementing GraphQL in Rails. It provides an expressive Ruby DSL for defining types, queries and mutations, along with native Rails integration via routes and controllers. Actively maintained by Robert Mosolgo, it's used by companies like GitHub and Shopify in production.

## 2. How to define an Object type in graphql-ruby to represent a User model?

**Answer**

An Object type in graphql-ruby inherits from Types::BaseObject and exposes fields via the field method. Each field specifies its name, GraphQL type (String, Int, ID, etc.) and nullability. This declarative approach allows precise control over which model data is exposed via the GraphQL API, ensuring clear separation between the ActiveRecord model and its GraphQL representation.

## 3. What is the main difference between a Query and a Mutation in GraphQL?

**Answer**

Queries are used to read data (GET operations) while Mutations are used to modify data (create, update, delete). By GraphQL convention, queries are idempotent and can be executed in parallel, whereas mutations are executed sequentially to guarantee the order of side effects. This distinction is fundamental for a well-designed GraphQL API.

## 17 more questions available

- How to declare a field with arguments in a graphql-ruby Query type?
- What major performance problem frequently occurs with GraphQL and ActiveRecord associations?

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## Other Ruby on Rails interview topics

- [Ruby Basics](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions/ruby-basics.md): 25 questions, Junior
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- [ActiveRecord Basics](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions/active-record-basics.md): 25 questions, Junior
- [Views & ERB Templates](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions/views-erb-templates.md): 20 questions, Junior
- [ActiveRecord Associations](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions/active-record-associations.md): 24 questions, Mid-Level
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