Union就是把不相干的一些数据实体，合并起来，一起供外部查询。不用像webapi，完成查询不同的数据，需要多次请求。一次请求，获取多样数据，减少请求次数，这也是GraphQL的优势之一。怎么弄，来来来，代码看过来：

using HotChocolate;using HotChocolate.Execution;using HotChocolate.Types;using System;namespace GraphQLBase006{    class Program    {        static void Main(string[] args)        {            UnionDemo.Run();        }    }    public class UnionDemo    {        public static void Run()        {            var schema = SchemaBuilder.New()                .AddQueryType
    
     ()                .AddType
     
      ()                .AddType
      
       ()                .AddType
       
        ()                .AddProjections()                .Create();            var executor = schema.MakeExecutable();            Console.WriteLine(executor.Execute(@"{    formats    {        __typename,        ... on Car{            brand,            price        },        ... on Cabbage{            name,            nutrition        }        ... on Earth{            diameter                }    } }").ToJson());        }    }    public class Query    {        public IUnion[] GetFormats()        {            return new IUnion[]            {                    new Car{                         Brand="Benz",                         Price=1000000                    },                    new Cabbage{                       Name="灰子白",                       Nutrition="纤维"                    },                                     new Earth{                      Diameter=12742                    }            };        }    }    [UnionType("Unio")]    public interface IUnion    {    }    public class Car : IUnion    {        public string Brand { get; set; }        public decimal Price { get; set; }    }    public class Cabbage : IUnion    {        public string Name { get; set; }        public string Nutrition { get; set; }    }    public class Earth : IUnion    {        public double Diameter { get; set; }       }}
       
      
     
    

案例中就是把不相干的Car,Cabbage,Earth，通过继承一个空接口合并起来，供外部访问，通过自定义查询接口语句，达到灵活取想要的数据，比如一些数据字典的查询就很有用，不相干的一些配置，同时获取到，以备后用。

结果：

{  "data": {    "formats": [      {        "__typename": "Car",        "brand": "Benz",        "price": 1000000      },      {        "__typename": "Cabbage",        "name": "\u7070\u5B50\u767D",        "nutrition": "\u7EA4\u7EF4"      },      {        "__typename": "Earth",        "diameter": 12742      }    ]  }}