GraphQL has gained immense popularity as an API query language due to its flexibility and efficiency. If you're preparing for a job that requires knowledge of GraphQL, it's crucial to understand not only the basics but also more advanced concepts. In this blog post, we'll explore some common GraphQL interview questions, ranging from introductory to advanced levels.
Basic Questions
1. What is GraphQL?
GraphQL is a query language for APIs and a runtime for executing those queries by using a type system you define for your data. It allows clients to request exactly the data they need and nothing more, making it more efficient than traditional REST APIs.
2. How does GraphQL differ from REST?
GraphQL allows clients to specify exactly what data they need, whereas REST APIs require multiple endpoints to fetch different resources. GraphQL can fetch related resources in a single request, reducing over-fetching and under-fetching of data.
3. What are the core components of GraphQL?
Schema: Defines the types and structure of the data available in the API.
Resolvers: Functions that handle the logic for fetching the data corresponding to a query.
Queries: Requests sent by the client to fetch data.
Mutations: Requests to modify data on the server.
Subscriptions: For real-time data updates via a published-subscribe model.
4. What is a schema in GraphQL?
A schema is a blueprint that defines the structure of the GraphQL API. It specifies the types, queries, mutations, and subscriptions that the API supports.
5. How do you define a type in GraphQL?
In GraphQL, a type is defined using the type keyword. For example:
type Book {
id: ID!
title: String!
author: Author!
}
Intermediate Questions
6. What is a resolver in GraphQL?
Resolvers are functions that resolve the values for fields in a GraphQL query. Each field in a query is backed by a resolver function that returns the data for that field.
const resolvers = {
Query: {
books: () => fetchBooks(),
},
Book: {
author: (parent) => fetchAuthorById(parent.authorId),
},
};
7. How do you handle errors in GraphQL?
Errors in GraphQL are handled by including an errors array in the response. Each error object can contain a message, locations, and path to help identify the issue.
8. What is the N+1 problem in GraphQL and how can you solve it?
The N+1 problem occurs when a resolver makes a separate database request for each item in a list, leading to performance issues. This can be solved using batching techniques like Facebook's DataLoader, which batches and caches database requests.
9. Explain the use of directives in GraphQL.
Directives provide a way to annotate fields and fragments with additional metadata. The most common directives are @include and @skip, which conditionally include or skip fields based on a boolean argument.
10. What are fragments in GraphQL?
Fragments are reusable units of a query that can be shared between multiple queries. They help reduce duplication in queries by allowing you to define common fields in one place.
fragment BookDetails on Book {
id
title
author {
name
}
}
query {
books {
...BookDetails
}
}
Advanced Questions
11. What is the difference between schema stitching and federation?
Schema Stitching: Combines multiple schemas into a single schema. It was the original method for merging schemas before federation.
Federation: An advanced approach by Apollo that allows multiple services to collaborate and share a unified graph.
12. How do you implement authentication and authorization in GraphQL?
Authentication is typically handled using JWT or OAuth tokens, which are passed in the headers of GraphQL requests. Authorization can be implemented within resolver functions by checking user roles and permissions before executing logic.
13. What are subscriptions in GraphQL, and how are they used?
Subscriptions are a way to receive real-time updates from a GraphQL server. They use a publish-subscribe model to listen for specific events and send updates to subscribed clients.
subscription {
bookAdded {
id
title
author {
name
}
}
}
14. How do you optimize performance in a GraphQL API?
Performance can be optimized by:
Using query batching and caching with tools like
DataLoader.Implementing pagination for large datasets.
Avoiding excessive nesting in queries.
Optimizing database queries within resolvers.
15. What are some common security concerns with GraphQL, and how can you mitigate them?
Query Complexity: Large, complex queries can overload the server. Mitigate by limiting query depth and complexity.
Introspection Exposure: Disable introspection in production to avoid exposing your schema.
Authorization Checks: Always perform authorization checks in resolvers to prevent unauthorized data access.
Conclusion
Preparing for a GraphQL interview involves understanding a range of concepts, from the basics of schemas and queries to advanced topics like schema federation and security. By familiarizing yourself with these questions and their answers, you'll be well-equipped to tackle any GraphQL-related queries in your interview.
Good luck with your interview preparation, and remember that hands-on practice with building and querying GraphQL APIs will solidify your understanding and improve your confidence.