Data source integration in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Querying a REST API data source

You have a GraphQL server that integrates a REST API providing user data. The REST API returns a list of users with fields id, name, and email. Which GraphQL query will correctly fetch the name and email of all users?

A { users { name email } }

B { users { id name email } }

C { users { username email } }

D { userList { name email } }

💡 Hint

Focus on the exact field names defined in the GraphQL schema for the REST API data.

The GraphQL query must match the schema fields exactly. The field users returns the list, and name and email are valid fields. Option A correctly queries these fields.

🧠 Conceptual

intermediate

Understanding GraphQL data source resolvers

In GraphQL, what is the main role of a resolver function when integrating an external data source like a database or REST API?

A It defines the schema types and fields for the data source.

B It fetches and returns the data for a specific field when queried.

C It validates the GraphQL query syntax before execution.

D It caches the entire data source to improve performance.

💡 Hint

Think about what happens when a GraphQL query asks for data.

Resolvers are functions that run when a field is requested in a query. They fetch and return the data from the connected data source.

📝 Syntax

advanced

Fixing a GraphQL schema integration error

Given this GraphQL schema snippet integrating a SQL database, which option correctly fixes the syntax error?

type Query {
  getUser(id: ID!): User
}

type User {
  id: ID!
  name: String
  email: String
}

A Add a resolver for getUser that accepts an argument and returns a User object.

B Remove the exclamation mark from <code>ID!</code> to make it optional.

C Change <code>getUser(id: ID!)</code> to <code>getUser: User</code> without arguments.

D Rename the type <code>User</code> to <code>Users</code> to match the database table.

💡 Hint

Consider what is needed to connect the schema to the data source properly.

The schema is correct, but to integrate with a SQL database, you must provide a resolver function for getUser that takes the id argument and returns the matching User. Other options either break the schema or do not fix the integration.

❓ optimization

advanced

Optimizing GraphQL data fetching from multiple sources

You have a GraphQL query that fetches user info from a REST API and order info from a SQL database. The current implementation makes separate calls for each user to fetch their orders, causing slow response times. What is the best optimization approach?

A Remove the order info from the query to speed up the response.

B Use multiple parallel calls for each user’s orders without batching.

C Cache the REST API responses indefinitely to avoid repeated calls.

D Batch the order requests by collecting all user IDs and fetching orders in a single query.

💡 Hint

Think about reducing the number of calls to the database.

Batching requests reduces the number of calls by fetching all needed orders in one query, improving performance. Caching indefinitely may cause stale data, removing data reduces functionality, and parallel calls still cause many requests.

🔧 Debug

expert

Debugging a GraphQL data source integration error

A GraphQL query to fetch products from a MongoDB data source returns null for the price field, but other fields like name and category return correctly. What is the most likely cause?

A The GraphQL schema does not define the <code>price</code> field in the <code>Product</code> type.

B The MongoDB collection does not contain the <code>price</code> field in documents.

C The resolver for <code>price</code> is missing or returns <code>null</code>.

D The query is missing the <code>price</code> field in the selection set.

💡 Hint

Check how each field gets its data from the database.

If other fields return correctly but price is always null, it usually means the resolver for price is missing or incorrectly implemented. The schema and query include price, and the database has the field, so the resolver is the issue.