GraphQL Resolvers: Core Concepts Quiz Quiz

Explore fundamental concepts and best practices related to GraphQL resolvers, their function in handling queries and mutations, and common scenarios faced when building GraphQL APIs. This quiz helps assess understanding of how resolvers work, their structure, and their role in the GraphQL execution process.

1. Resolver Function Purpose

   In the context of a GraphQL API, what is the main role of a resolver function when a client requests the 'user' field in a query?

   1. To fetch and return the appropriate data for the 'user' field
   2. To define the structure of the 'user' field in the schema
   3. To generate a query string for the client
   4. To specify the order of the fields returned to the client

   Explanation: Resolvers are responsible for retrieving and returning data for specific fields requested in a GraphQL query, making option C correct. Defining structure (option A) is done in the schema, not the resolver. The order of returned fields (option B) is determined by the query itself, not the resolver. Generating a query string (option D) is a task for the client, not the resolver.

2. Resolver Function Parameters

   Which set of parameters is typically received by a GraphQL resolver function when processing a field, such as in 'user(id: 1)'?

   1. parent, args, context, info
   2. user, query, result, options
   3. request, response, context, field
   4. root, data, error, schema

   Explanation: A standard resolver function receives four arguments: parent, args, context, and info, which allow it to access relevant data and execution details. Option B includes web server concepts like request and response, which are not specific to GraphQL resolvers. Option C lists terms not used consistently in resolver signatures. Option D includes user and query, which are not appropriate for a resolver's parameter list.

3. Default Resolver Behavior

   If no custom resolver is defined for a field in a GraphQL type and the field's name matches a property in the returned object, what does the GraphQL execution engine do?

   1. It uses a default resolver to fetch the property value
   2. It automatically creates a database query
   3. It ignores the field and returns null
   4. It throws an error and stops execution

   Explanation: The execution engine uses a default resolver, which looks up a property with the same name as the field on the returned object. Ignoring the field or returning null (option A) is not the default behavior. Throwing an error (option C) only occurs for schema violations or execution errors, not for missing custom resolvers. Database queries (option D) are not automatically generated; resolvers manage how and when to access external data.

4. Nested Resolvers Scenario

   Given a query for a 'post' with an embedded 'author' object, how does GraphQL typically resolve both fields?

   1. It runs the 'post' resolver first, then invokes the 'author' resolver within each 'post' object
   2. It skips the 'author' field if a resolver is missing for 'post'
   3. It flattens all fields into a top-level response
   4. It executes a single resolver for both 'post' and 'author' simultaneously

   Explanation: When resolving nested fields, GraphQL first runs the parent 'post' resolver to fetch the post object, then invokes the 'author' resolver for each post to retrieve author details. Simultaneous execution (option A) is not the standard approach; fields are resolved hierarchically. Option B incorrectly suggests skipping fields, and option D misrepresents how responses are structured in GraphQL.

5. Resolver Return Values

   What is the expected return value of a resolver for a field declared as a list of integers, such as '[Int]' in the schema?

   1. A string representing comma-separated numbers
   2. An array of integers
   3. An object containing integer properties
   4. A single integer value

   Explanation: For a field marked as a list of integers, the resolver should return an array of integers to match the schema's type expectations. A comma-separated string (option A) does not match the type and would result in a type error. Returning a single integer (option B) only satisfies a scalar field, not a list. Returning an object (option D) does not conform to a list type in GraphQL.