Inheritance.md

Inheritance

Interfaces

Assumes we have next GraphQL types:

interface Product {
  manufacturer: String!
}
type Smartphone implements Product {
  manufacturer: String!
  operationSystem: String!
}
type EReader implements Product {
  manufacturer: String!
  inkType: String!
}

C# model for it will be like this:

abstract class Product
{
    public string Manufacturer { get; set; }
}
class Smartphone: Product
{
    public string OperationSystem { get; set; }
}
class EReader: Product
{
    public string InkType { get; set; }
}

As you can see, GraphQL interface Product in C# model defined as abstract class. Now when you will fetch data from GraphQL endpoint, for each member of type Product field __typename will be included automatically. For example this code

context.Get<Product>().ToArray();

will generate query

query {
  products {
    __typename
    manufacturer
    ... on Smartphone {
      operationSystem
    }
    ... on EReader {
      inkType
    }
  }
}

Unions

Assumes we have next GraphQL types:

type Smartphone {
  manufacturer: String!
  operationSystem: String!
}
type EReader {
  manufacturer: String!
  inkType: String!
}
union Product = Smartphone | EReader

C# model for it will be same as above for interface types. It's important to keep in mind that C# types Smartphone and EREader must have common base type (like Product). Now when you will fetch data from endpoint, next query will be generated

query {
  products {
    __typename
    ... on Smartphone {      
      manufacturer
      operationSystem
    }
    ... on EReader {
      manufacturer
      inkType
    }
  }
}

Deep inheritance

Deep inheritance in GraphQL is not supported. But you can use deep inheritance in C# model. For example, we have this GraphQL types

interface Product {
  manufacturer: String!
}
type Smartphone implements Product {
  manufacturer: String!
  operationSystem: String!
  eSim: Boolean!
}
type Tablet implements Product {
  manufacturer: String!
  operationSystem: String!
  hasKeyboard: Boolean!
}
type EReader implements Product {
  manufacturer: String!
  inkType: String!
}

As you can see, types Smartphone and Tablet can be generalized by common parent type, e.g. SmartDevice. So, in C# model you can define next types

abstract class Product
{
    public string Manufacturer { get; set; }
}
class EReader: Product
{
    public string InkType { get; set; }
}
abstract class SmartDevice: Product
{
    public string OperationSystem { get; set; }
}
public class Smartphone: SmartDevice
{
    public bool ESim { get; set; }
}
public class Tablet: SmartDevice
{
    public bool HasKeyboard { get; set; }
}

Important notes

• For correct work of inheritance model all type must be configured as discribed in this section.