Input arguments for mutations in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Mutation with required input argument

Given the following GraphQL mutation schema, what will be the result of this mutation call?

mutation {
  addUser(name: "Alice") {
    id
    name
  }
}

Schema snippet:

type Mutation {
  addUser(name: String!): User
}
type User {
  id: ID!
  name: String!
}

A {"data": {"addUser": {"id": "1", "name": "Alice"}}}

B {"data": {"addUser": null}}

C {"errors": [{"message": "Field 'addUser' argument 'name' of type 'String!' is required but not provided."}]}

D {"data": {"addUser": {"id": null, "name": "Alice"}}}

💡 Hint

The mutation requires a non-null string argument 'name'.

The mutation 'addUser' requires a non-null 'name' argument. Providing 'Alice' returns a new User object with id and name.

📝 Syntax

intermediate

Identify the syntax error in mutation input

Which option contains a syntax error in the mutation input arguments?

GraphQL

mutation {
  updateUser(id: 5, name: "Bob") {
    id
    name
  }
}

A mutation { updateUser(id: 5, name: Bob) { id name } }

B mutation { updateUser(id: "5", name: "Bob") { id name } }

C mutation { updateUser(id: 5, name: "Bob") { id name } }

D mutation { updateUser(id: 5 name: "Bob") { id name } }

💡 Hint

Check the commas between arguments and string quoting.

Option D is missing a comma between arguments 'id: 5' and 'name: "Bob"', causing a syntax error.

❓ optimization

advanced

Optimizing mutation input for multiple fields

You want to update a user's profile with many fields: name, email, age, and address. Which input argument style is best for scalability and clarity?

A mutation { updateUser(id: 1, input: {name: "Eve", email: "[e-mail]", age: 30, address: "123 St"}) { id name } }

B mutation { updateUser(id: 1, name: "Eve", email: "[e-mail]", age: 30, address: "123 St") { id name } }

C mutation { updateUser({id: 1, name: "Eve", email: "[e-mail]", age: 30, address: "123 St"}) { id name } }

D mutation { updateUser(id: 1, fields: ["name", "email", "age", "address"], values: ["Eve", "[e-mail]", 30, "123 St"]) { id name } }

💡 Hint

Consider grouping related fields into one input object.

Using a single input object argument (option A) is clearer and easier to extend than listing many separate arguments.

🔧 Debug

advanced

Why does this mutation fail?

Given this mutation call:

mutation {
  createPost(title: "Hello") {
    id
    title
  }
}

And this schema snippet:

type Mutation {
  createPost(input: PostInput!): Post
}
input PostInput {
  title: String!
  content: String!
}
type Post {
  id: ID!
  title: String!
  content: String!
}

Why does the mutation fail?

A The mutation does not provide the 'input' argument as required by the schema.

B The mutation is missing the required 'content' field inside the 'input' argument.

C All of the above.

D The mutation uses 'title' as a direct argument instead of inside 'input'.

💡 Hint

Check how the mutation arguments match the schema.

The mutation must provide a single 'input' argument of type PostInput with both 'title' and 'content'. The call provides 'title' directly and omits 'content'.

🧠 Conceptual

expert

Understanding input argument types in mutations

Which statement about input arguments in GraphQL mutations is TRUE?

A You cannot use lists as input arguments in mutations.

B Input object types can be used as arguments to group multiple fields into one argument.

C Mutation input arguments must always be nullable to allow partial updates.

D Scalar types cannot be used as mutation input arguments.

💡 Hint

Think about how to organize multiple fields in mutation inputs.

Input object types are designed to group multiple related fields into one argument. Scalars and lists can also be used, and arguments can be non-null.