Parent (root) argument in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Understanding the root parent argument in GraphQL resolver

Given the following GraphQL resolver snippet, what will be the value of the parent argument when resolving the user field in the root query?

GraphQL

const resolvers = {
  Query: {
    user(parent, args, context, info) {
      return { id: args.id, name: "Alice" };
    }
  }
};

A An empty object {}

B undefined

C The root query object

D null

💡 Hint

Think about what the parent argument represents at the root level of a GraphQL query.

At the root level, the parent argument is undefined because there is no parent object above the root query.

❓ query_result

intermediate

Parent argument value in nested GraphQL resolvers

Consider this GraphQL schema and resolver snippet. What will be the value of the parent argument when resolving the posts field inside the User type?

GraphQL

const resolvers = {
  Query: {
    user(parent, args) {
      return { id: 1, name: "Bob" };
    }
  },
  User: {
    posts(parent, args) {
      return [{ id: 101, title: "Hello" }];
    }
  }
};

A The root query object

B null

C undefined

D The user object { id: 1, name: "Bob" }

💡 Hint

The parent argument in nested resolvers is the object returned by the parent field resolver.

When resolving nested fields, the parent argument is the object returned by the previous resolver, here the user object.

📝 Syntax

advanced

Identify the syntax error in resolver using parent argument

Which option contains a syntax error in the way the parent argument is used in this resolver function?

GraphQL

const resolvers = {
  User: {
    posts(parent, args) {
      return parent.posts;
    }
  }
};

A posts(parent args) { return parent.posts; }

B posts(parent, args) { return parent.posts; }

C posts(parent, args) => { return parent.posts; }

D posts: function(parent, args) { return parent.posts; }

💡 Hint

Check the function parameter list syntax carefully.

Option A is missing a comma between parameters, causing a syntax error.

❓ optimization

advanced

Optimizing resolver usage of parent argument to avoid redundant database calls

Given a resolver for User.posts that fetches posts from the database, which option best uses the parent argument to avoid fetching the user again inside the posts resolver?

GraphQL

const resolvers = {
  Query: {
    user(parent, args) {
      return db.getUserById(args.id);
    }
  },
  User: {
    posts(parent, args) {
      // Which option below is best?
    }
  }
};

A return db.getPostsByUserId(args.userId);

B const user = db.getUserById(parent.id); return db.getPostsByUserId(user.id);

C return db.getPostsByUserId(parent.id);

D return db.getPosts();

💡 Hint

Use the parent argument to get the user id directly.

Option C uses the parent object passed from the user resolver, avoiding an extra database call.

🧠 Conceptual

expert

Why is the parent argument null at the root level in GraphQL?

In GraphQL, the parent argument in resolvers is undefined at the root query level. Why is this the case?

A Because the root query has no parent object above it in the query execution hierarchy.

B Because the parent argument is only used for mutations, not queries.

C Because the parent argument is deprecated and replaced by context.

D Because the parent argument is always an empty object at the root.

💡 Hint

Think about the structure of a GraphQL query and how resolvers are called.

The root query is the top-level entry point, so it has no parent object; hence parent is undefined.