Input types in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this GraphQL mutation with input type?

Given the following GraphQL mutation and input type, what will be the returned data?

input NewUserInput {
  username: String!
  age: Int
}

mutation CreateUser($input: NewUserInput!) {
  createUser(input: $input) {
    id
    username
    age
  }
}

Variables:

{"input": {"username": "alice", "age": 30}}

GraphQL

input NewUserInput {
  username: String!
  age: Int
}

mutation CreateUser($input: NewUserInput!) {
  createUser(input: $input) {
    id
    username
    age
  }
}

A {"data": {"createUser": {"id": "1", "username": null, "age": 30}}}

B {"data": {"createUser": {"id": "1", "username": "alice"}}}

C {"errors": [{"message": "Field 'age' is required"}]}

D {"data": {"createUser": {"id": "1", "username": "alice", "age": 30}}}

💡 Hint

Check which fields are required and what the mutation returns.

The input type requires 'username' but 'age' is optional. The mutation returns all requested fields including 'age' if provided.

📝 Syntax

intermediate

Which option is a valid GraphQL input type definition?

Choose the valid syntax for defining an input type in GraphQL.

A

input UserInput {
  name: String!
  email: String
}

B

}
gnirtS :liame  
!gnirtS :eman  
{ tupnIresU tupni

C

input UserInput {
  name: String!
  email: String!
  age
}

D

type UserInput {
  name: String!
  email: String
}

💡 Hint

Remember input types use the keyword input and fields must have types.

Option A correctly uses input keyword and specifies field types properly. Option A uses type which is for object types, not input. Option A misses type for age. Option A misses colon after name.

❓ optimization

advanced

How to optimize input types for nested objects in GraphQL?

You want to create a mutation that accepts a user with an address. Which input type design is best for performance and clarity?

A

input UserInput {
  name: String!
  street: String
  city: String
}

B

input UserInput {
  name: String!
  address: AddressInput
}

input AddressInput {
  street: String
  city: String
}

C

input UserInput {
  name: String!
  address: String
}

D

type UserInput {
  name: String!
  address: AddressInput
}

input AddressInput {
  street: String
  city: String
}

💡 Hint

Consider reusability and clear structure for nested data.

Option B uses nested input types properly, improving clarity and reusability. Option B flattens address fields which can be less clear. Option B uses a string for address which loses structure. Option B uses 'type' instead of 'input' for UserInput, which is invalid for inputs.

🔧 Debug

advanced

Why does this GraphQL query with input type cause an error?

Given this input type and mutation, why does the following query cause an error?

input ProductInput {
  name: String!
  price: Float!
}

mutation AddProduct($input: ProductInput!) {
  addProduct(input: $input) {
    id
    name
    price
  }
}

Variables:

{"input": {"name": "Book"}}

A No error, mutation succeeds with price as null.

B Error: Field 'name' is missing.

C Error: Field 'price' of required type 'Float!' was not provided.

D Error: Input type 'ProductInput' is not defined.

💡 Hint

Check which fields are required and if all required fields are provided.

The 'price' field is marked as non-nullable (Float!) but is missing in the variables, causing an error.

🧠 Conceptual

expert

What is the main difference between GraphQL input types and object types?

Choose the statement that best explains the difference between input types and object types in GraphQL.

A Input types are used for passing data into queries or mutations, and cannot have fields that are other object types; object types define the shape of data returned by the server.

B Input types and object types are interchangeable and can be used anywhere in the schema without restrictions.

C Object types are only for mutations, while input types are only for queries.

D Input types can have resolvers, but object types cannot.

💡 Hint

Think about where input types and object types are used in GraphQL operations.

Input types are designed for input data and cannot contain fields that are object types (only other input types or scalars). Object types define the data shape returned by queries or mutations. They are not interchangeable.