Why databases back GraphQL - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why do GraphQL servers often rely on databases?

GraphQL servers need to provide data to clients. Why is it common for GraphQL servers to use databases as their data source?

A Because databases automatically convert GraphQL queries into REST API calls.

B Because GraphQL can only work with SQL databases and no other data sources.

C Because GraphQL servers do not need any data source to respond to queries.

D Because databases store structured data that GraphQL queries can retrieve efficiently.

💡 Hint

Think about where data is usually stored in applications.

GraphQL servers use databases because databases hold the actual data in a structured way. GraphQL queries ask for specific data, and databases can efficiently provide that data.

❓ query_result

intermediate

What data does this GraphQL query return from the database?

Given a GraphQL query requesting user { id, name } and a database table users with columns id, name, and email, what will the query return?

GraphQL

query {
  user {
    id
    name
  }
}

A [{ "id": 1, "name": "Alice", "email": "[e-mail]" }]

B [{ "id": 1, "name": "Alice" }, { "id": 2, "name": "Bob" }]

C [{ "email": "[e-mail]" }]

D []

💡 Hint

The query only asks for id and name, not email.

The GraphQL query requests only the id and name fields. The database returns those fields for each user.

📝 Syntax

advanced

Identify the error in this GraphQL resolver accessing a database

Look at this resolver code snippet that fetches data from a database. What is the syntax error?

GraphQL

const resolvers = {
  Query: {
    user: (parent, args, context) => {
      return context.db.query('SELECT * FROM users WHERE id = $1', args.id)
    }
  }
}

A The function should be async to await the database query.

B The resolver is missing a return statement.

C The query method should use an array for parameters, like [args.id] instead of args.id.

D The context object cannot be used inside resolvers.

💡 Hint

Check how parameters are passed to parameterized queries.

Database query methods usually expect parameters as an array. Passing args.id directly is incorrect syntax.

❓ optimization

advanced

How to optimize GraphQL queries backed by databases to reduce load?

When a GraphQL query requests nested data (e.g., users and their posts), what is a common optimization to reduce database load?

A Use data loader techniques to batch and cache database requests.

B Run separate database queries for each nested field without caching.

C Fetch all data in one big query without filtering.

D Avoid using databases and hardcode data in resolvers.

💡 Hint

Think about how to avoid many repeated database calls.

Data loader batches multiple requests into one and caches results, reducing database load and improving performance.

🔧 Debug

expert

Why does this GraphQL query fail when backed by a database?

This GraphQL query requests a user by ID, but it returns null even though the user exists in the database. What is the likely cause?

GraphQL

query {
  user(id: 5) {
    id
    name
  }
}

A The resolver does not correctly use the argument 'id' to query the database.

B The user ID 5 does not exist in the database.

C GraphQL does not support arguments in queries.

D The database table is empty.

💡 Hint

Check how the resolver uses the query arguments.

If the resolver ignores or misuses the 'id' argument, the database query will not find the user, returning null.