Input Objects

GraphQL defines input object types to allow us to use objects as arguments on our fields.

Input object types can be defined like the following:

public class BookInput
{
    public string Title { get; set; }

    public string Author { get; set; }
}

public class Mutation
{
    public async Task<Book> AddBook(BookInput input)
    {
        // Omitted code for brevity
    }
}

info

If a class is used as an argument to a resolver and it does not end in Input, Hot Chocolate (by default) will append Input to the type name in the resulting schema.

We can also use a class both as an output- and an input-type:

public class Book
{
    public string Title { get; set; }

    public string Author { get; set; }
}

public class Mutation
{
    public async Task<Book> AddBook(Book input)
    {
        // Omitted code for brevity
    }
}

This will produce the following schema:

type Book {
  title: String
  author: String
}

input BookInput {
  title: String
  author: String
}

type Mutation {
  addBook(input: BookInput): Book
}

danger

While it is possible, it is not encouraged, as it complicates future extensions of either type.

`OneOf` Input Objects

OneOf Input Objects are a special variant of Input Objects where the type system asserts that exactly one of the fields must be set and non-null, all others being omitted. This is represented in introspection with the __Type.oneField: Boolean field, and in SDL via the @oneOf directive on the input object.

This introduces a form of input polymorphism to GraphQL. For example, the following PetInput input object lets you choose between a number of potential input types:

input PetInput @oneOf {
  cat: CatInput
  dog: DogInput
  fish: FishInput
}

input CatInput {
  name: String!
  numberOfLives: Int
}
input DogInput {
  name: String!
  wagsTail: Boolean
}
input FishInput {
  name: String!
  bodyLengthInMm: Int
}

type Mutation {
  addPet(pet: PetInput!): Pet
}

Since the OneOf Input Objects RFC is not yet in the draft stage it is still an opt-in feature. In order to activate it set the schema options to enable it:

builder.Services
    .AddGraphQLServer()
    ...
    .ModifyOptions(o => o.EnableOneOf = true);

Once activate you can create Oneof Input Objects like the following:

[OneOf]
public class PetInput
{
    public Dog? Dog { get; set; }

    public Cat? Cat { get; set; }
}

public interface IPet
{
    string Name { get; }
}

public class Dog : IPet
{
    public string Name { get; set; }
}

public class Cat : IPet
{
    public string Name { get; set; }
}

public class Mutation
{
    public Task<IPet> CreatePetAsync(PetInput input)
    {
        // Omitted code for brevity
    }
}

OneOf Input Objects​

`OneOf` Input Objects