TypeGen — GraphQL emitter

TypeTarget.GraphQL emits GraphQL SDL .graphql files from C# DTOs — types, enums, and their relationships. Useful when your C# models are the source of truth and you need a matching GraphQL schema for a gateway, federation layer, or schema-first GraphQL server.

[GenerateTypes(Targets = TypeTarget.GraphQL, OutputDir = "../schema")]
public class Order
{
    public Guid Id { get; set; }
    public string Customer { get; set; } = "";
    public OrderStatus Status { get; set; }
    public DateTime CreatedAt { get; set; }
    public List<LineItem> Lines { get; set; } = [];
    public string? Note { get; set; }
}

public enum OrderStatus
{
    Pending,
    Confirmed,
    Shipped,
    Cancelled
}

public class LineItem
{
    public int ProductId { get; set; }
    public int Quantity { get; set; }
    public decimal Price { get; set; }
}

schema.graphql

type Order {
  id: ID!
  customer: String!
  status: OrderStatus!
  createdAt: DateTime!
  lines: [LineItem!]!
  note: String
}

enum OrderStatus {
  PENDING
  CONFIRMED
  SHIPPED
  CANCELLED
}

type LineItem {
  productId: Int!
  quantity: Int!
  price: Float!
}

Type mapping

C#	GraphQL
int, short, byte	Int
long	Int (GraphQL has no native long — use custom scalar if needed)
float, double, decimal	Float
string	String
bool	Boolean
Guid	ID
DateTime, DateTimeOffset	DateTime (custom scalar)
DateOnly	Date (custom scalar)
TimeOnly	Time (custom scalar)
T? (nullable)	field without !
non-nullable	field with !
List<T>, T[], IEnumerable<T>	[T!]!
List<T>?	[T!]
Dictionary<string, V>	JSON (custom scalar — no native map in GraphQL)
user DTO	named type reference
enum	enum with UPPER_SNAKE_CASE values

File layout

SingleFile (default) — all types emitted into one .graphql file:

[GenerateTypes(Targets = TypeTarget.GraphQL, OutputDir = "../schema")]
public class Order { ... }
// → ../schema/schema.graphql (contains Order, OrderStatus, LineItem, etc.)

FilePerType — one .graphql file per type/enum:

b.GraphQL(g =>
{
    g.FileLayout = GraphQLFileLayout.FilePerType;
    g.OutputDir = "../schema/types";
});
// → ../schema/types/Order.graphql
// → ../schema/types/OrderStatus.graphql
// → ../schema/types/LineItem.graphql

Configuration

b.GraphQL(g =>
{
    g.OutputDir = "../schema";
    g.FileLayout = GraphQLFileLayout.SingleFile;   // default; or FilePerType
    g.SingleFileName = "schema.graphql";           // default output file name
    g.EnumCasing = GraphQLEnumCasing.UpperSnake;   // default; PENDING, CONFIRMED, ...
    g.EmitDescriptions = true;                     // emit C# <summary> as GraphQL descriptions
    g.CustomScalars = true;                        // default; emit scalar DateTime / Date / Time / JSON declarations
});

When CustomScalars is enabled (the default), the emitter prepends scalar declarations for non-standard types used in the schema:

scalar DateTime
scalar Date
scalar JSON

type Order {
  ...
}

Set CustomScalars = false if your GraphQL server already defines these scalars and you want to avoid duplicates.