UnionType

type FieldValue1 {
	property: Int!
}

type FieldValue2 {
	method(arg1: Int!): Int!
}

union FieldType = FieldValue1 | FieldValue2

Generated

• Marker model interface used to indicate that the type can be be member of an union type
• Controller interface with method for getting the actual Type System type of the union member
• Default implementation of the controller interface

Model

Marker interface is generated to provide common base interface for members of the union. Each member of the union will implement this interface.

public partial interface IFieldType
{
    public string __Typename => "FieldType";
}

public partial class FieldValue1 : IFieldType
{
    //...
}

public partial class FieldValue2 : IFieldType
{
    //...
}

Controller

GraphQL execution requires to know the actual type of the union member during value completion. Controller interface is generated with IsTypeOf method to resolve the actual type. This is similar to interfaces.

public partial interface IFieldTypeController
{
    INamedType IsTypeOf(IFieldType instance, ISchema schema);
}

Default Controller implementation

Default implementation of the union controller uses the generated __Typename property to fetch the named type from the schema.

public partial class FieldTypeController : IFieldTypeController
{
    public INamedType IsTypeOf(IFieldType instance, ISchema schema)
    {
        return schema.GetNamedType(instance.__Typename);
    }
}