20 Apollo GraphQL Interview Questions and Answers

Prepare for the types of questions you are likely to be asked when interviewing for a position where Apollo GraphQL will be used.

Apollo GraphQL is a popular open-source data query and manipulation language for APIs. If you are applying for a position that involves working with Apollo GraphQL, you should expect to be asked questions about it during your interview. In this article, we will review some of the most common Apollo GraphQL interview questions and provide tips on how to answer them.

Apollo GraphQL Interview Questions and Answers

Here are 20 commonly asked Apollo GraphQL interview questions and answers to prepare you for your interview:

1. What is GraphQL?

GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL provides a complete and understandable description of the data in your API, gives clients the power to ask for exactly what they need and nothing more, makes it easier to evolve APIs over time, and enables powerful developer tools.

2. Can you explain the main features of GraphQL?

GraphQL is a query language for APIs that allows clients to request specific data from a server. It also allows for the creation of new data on the server. GraphQL is often used in place of REST APIs because it offers a more flexible way to request data.

3. How does GraphQL compare with RESTful services?

GraphQL is a newer technology, and it offers a number of advantages over RESTful services. For one, it is much more flexible, allowing you to query for exactly the data you need, and nothing more. It also eliminates the need for multiple round trips to the server, since you can batch your queries together. Finally, it is easier to use with modern front-end frameworks such as React and Angular.

4. What are some use cases for GraphQL?

GraphQL can be used for any application that needs to fetch data from a server. It is especially well suited for mobile applications that need to fetch data from multiple sources, as it allows the client to specify exactly what data it needs. GraphQL is also useful for applications that have complex data dependencies, as it allows the client to request only the data that it needs.

5. What’s the difference between a schema and an API in GraphQL?

A schema is a blueprint for your data that defines the types, relationships, and fields that your data will have. An API is a way to access your data that uses the schema as a guide.

6. Can you explain what Apollo Server is used for?

Apollo Server is a tool used for creating and managing GraphQL servers. It can be used to create a new GraphQL server from scratch, or to add GraphQL capabilities to an existing server. Apollo Server provides a number of features, including the ability to define a schema, query data, and add resolvers.

7. Can you give me some examples of real-world applications that use GraphQL?

Some well-known companies that use GraphQL in their applications include Facebook, GitHub, and Shopify.

8. Can you explain how to create a simple GraphQL server using Express?

There are a few different ways to set up a GraphQL server using Express, but the most basic way is to use the express-graphql middleware. This middleware will allow you to define a GraphQL schema and then handle any incoming GraphQL queries. You will also need to define a route for the middleware to be mounted on, and then you can start your server as usual.

9. What do you understand about graph databases and their relationship to GraphQL?

Graph databases are databases that store data in a graph structure, with nodes representing entities and edges representing the relationships between them. GraphQL is a query language that is used to interact with graph databases, allowing you to fetch and update data in the database.

10. Are there any alternatives to GraphQL? If yes, then which ones?

There are a few alternatives to GraphQL, such as Falcor from Netflix, and REST. However, GraphQL has become the standard for API design, so most new development is focused on GraphQL.

11. Is it possible to integrate GraphQL with other frameworks like Django or Rails?

Yes, it is possible to integrate GraphQL with other frameworks like Django or Rails. There are a few different ways to do this, but one popular way is to use the graphql-ruby gem. This gem allows you to use GraphQL within your Ruby on Rails applications.

12. What do you understand about mutations and queries in GraphQL?

Mutations are used to modify data on the server, while queries are used to fetch data from the server. In order to execute a mutation, you will need to use the keyword mutation, followed by the name of the mutation and the input parameters. A query is similar, but you will use the keyword query and provide the name of the query and the input parameters.

13. How do you build a client app in ReactJS using GraphQL?

The first step is to install the Apollo client library, which can be done with the following command:

npm install apollo-client –save

Once the Apollo client is installed, you need to create a new Apollo client instance and pass it your GraphQL endpoint:

const client = new ApolloClient({
uri: ‘’

After that, you can use the Apollo client instance in your React components to fetch data from your GraphQL endpoint:

class MyComponent extends React.Component {
render() {
return (

// …


14. What are the advantages of using GraphQL over other query languages?

GraphQL has a number of advantages over other query languages. First, it allows for much more flexibility in terms of the data that can be queried. Second, it is much easier to use than other query languages, making it more accessible to developers. Finally, GraphQL is much more efficient in terms of the amount of data that needs to be transferred, making it ideal for use in mobile applications.

15. Are there any disadvantages of using GraphQL?

While GraphQL has a lot of advantages, there are a few potential disadvantages to using it. First, because it is a relatively new technology, there is a lack of tooling and documentation compared to more established technologies. This can make it more difficult to get started with GraphQL. Additionally, GraphQL can be more complex to set up than a traditional REST API, and it requires a bit more work to optimize for performance.

16. What do you need to know before learning GraphQL?

Before learning GraphQL, you should have a basic understanding of the following:

– What is an API?
– What is a REST API?
– What is a GraphQL API?
– What are the benefits of using a GraphQL API?
– How does a GraphQL API differ from a REST API?
– What are some of the most popular GraphQL tools and libraries?

17. What is your opinion on fetching data from multiple sources using GraphQL?

I believe that fetching data from multiple sources using GraphQL can be a great way to get the data that you need while still keeping your code clean and organized. It can also help to reduce the amount of code that you need to write, which can save you time and effort in the long run.

18. What are the various types of errors that can occur when executing queries in GraphQL?

The various types of errors that can occur when executing queries in GraphQL are:

– Syntax Errors: These occur when the query is not well-formed and cannot be parsed by the GraphQL engine.
– Validation Errors: These occur when the query is well-formed but does not adhere to the rules set by the schema.
– Execution Errors: These occur when there is an error during the execution of the query, such as a database error.

19. What are the different ways of defining variables in GraphQL?

There are two ways of defining variables in GraphQL:

1. In the query string: variables can be defined in the query string itself, using the $variableName syntax.

2. In the operation definition: variables can be defined in the operation definition (i.e. inside the query/mutation/subscription block), using the variable keyword, followed by the variable name, type, and default value.

20. Can you explain what fragments are in the context of GraphQL?

In GraphQL, a fragment is a piece of a GraphQL document that is used to group fields together. Fragments are used to avoid duplication when writing GraphQL queries, and they can be used to split up large queries into smaller pieces.


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