They retrieve data requested in queries. They implement mutations to create, update, or delete data. They control how data is processed or formatted before being sent to the client. Schema: type Query { getUser(id: ID!): User } type User { id: ID! name: String! email: String! } //resolver const resolvers = { Query: { getUser: async (_, { id }, context) => { // Fetch the user from a database const user = await context.db.findUserById(id); return user; }, }, }; Query Resolvers: Handle fetching data (e.g.,getUser , listPosts ). Mutation Resolvers: Handle modifying data (e.g., createUser, updatePost). Field Resolvers: Resolve specific fields, particularly if they require custom logic (e.g., nested fields like post.author)

What are resolvers?

Difficulty: 6/10

resolver functions, data fetching, error handling

In GraphQL, resolvers are functions that handle the logic for retrieving or manipulating data based on the queries, mutations, or subscriptions defined in your GraphQL schema. Resolvers act as the connection between your GraphQL API and the underlying data sources, such as databases, REST APIs, or other services.

What do they do:

1
They retrieve data requested in queries.
2
They implement mutations to create, update, or delete data.
3
They control how data is processed or formatted before being sent to the client.

Example of a resolver:

Types of resolvers:

1
Query Resolvers: Handle fetching data (e.g.,getUser , listPosts ).
2
Mutation Resolvers: Handle modifying data (e.g., createUser, updatePost).
3
Field Resolvers: Resolve specific fields, particularly if they require custom logic (e.g., nested fields like post.author)

Scenario Questions

0-2 years experience

1We have a simple GraphQL schema with a `User` type that has `id` and `name`. How would you write a resolver to fetch a user by ID from an in‑memory array?
2If you omit a resolver for a scalar field like `name`, what does GraphQL do when that field is requested?
3When a query asks for `user { id name }` and your resolver for `user` returns `null`, what will the response look like?

Follow-up Questions

Can you give an example of when you'd rely on the default resolver?
How would you expose the same resolver logic to both GraphQL and a REST endpoint?
What monitoring would you add around resolver execution?