GraphQL 既是一种用于 API 的查询语言也是一个满足你数据查询的运行时。GraphQL 对你的 API 中的数据提供了一套易于理解的完整描述，使得客户端能够准确地获得它需要的数据，而且没有任何冗余，也让 API 更容易地随着时间推移而演进，还能用于构建强大的开发者工具。
——出自 https://graphql.cn
数据是有关系的，可以利用HotChocolate.Stitching功能，把业务逻辑相关联的实体数据，从后台的两个服务中关联起来，这有点api网关的组合功能，可以把前端的一次请求，分解成后端的多次请求，并把数据组合后返回回去。
下面有这样一个例子：有个学生服务，有两个api，一个是查询全部学生，一个是按学号查询学生；另一个是成绩服务，有两个api，一个是按学号查询这个学生的全部成绩，一个是按id查询成绩。现在可以在学生实体中组合成绩，也可以在成绩实体中组合学生，这是因为学生和成绩是一个一对多的关系。
下面来看实例：
学生服务：GraphQLDemo03_Students
引入NuGet
HotChocolate.AspNetCore
HotChocolate.Data
Starup.cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;namespace GraphQLDemo03_Students
{public class Startup{ public void ConfigureServices(IServiceCollection services){services.AddSingleton<IStudentRepository, StudentRepository>().AddGraphQLServer().AddQueryType<Query>() ;}public void Configure(IApplicationBuilder app, IWebHostEnvironment env){if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseRouting();app.UseEndpoints(endpoints =>{endpoints.MapGraphQL();});}}
}
Query.cs
using HotChocolate;
using System.Collections.Generic;namespace GraphQLDemo03_Students
{public class Query{ public IEnumerable<Student> GetStudents([Service] IStudentRepository studentRepository){return studentRepository.GetStudents();}public Student GetStudent(string stuNo, [Service] IStudentRepository studentRepository){return studentRepository.GetStudent(stuNo);}}
}
StudentRepository.cs
using System.Collections.Generic;
using System.Linq;namespace GraphQLDemo03_Students
{public interface IStudentRepository{IEnumerable<Student> GetStudents();Student GetStudent(string stuNo);}public class StudentRepository : IStudentRepository{public IEnumerable<Student> GetStudents(){var students = new List<Student>() {new Student("S0001","小张",20,true),new Student("S0002","小李",19,false),};return students;}public Student GetStudent(string stuNo){var students = new List<Student>() {new Student("S0001","小张",20,true),new Student("S0002","小李",19,false),};return students.SingleOrDefault(s => s.StuNo == stuNo);}}public record Student(string StuNo, string Name, int Age, bool Sex);
}成绩服务：GraphQLDemo03_Grades
引入NuGet包
HotChocolate.AspNetCore
HotChocolate.Data
Startup.cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;namespace GraphQLDemo03_Grades
{public class Startup{public void ConfigureServices(IServiceCollection services){services.AddSingleton<IGradeRepository, GradeRepository>() .AddGraphQLServer() .AddQueryType<Query>();} public void Configure(IApplicationBuilder app, IWebHostEnvironment env){if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseRouting();app.UseEndpoints(endpoints =>{endpoints.MapGraphQL();});}}
}
Query.cs
using HotChocolate;
using System.Collections.Generic;namespace GraphQLDemo03_Grades
{ public class Query{public IEnumerable<Grade> GetGrades([Service] IGradeRepository gradeRepository, string stuNo){return gradeRepository.GetGrades(stuNo);}public Grade GetGrade([Service] IGradeRepository gradeRepository, int id){return gradeRepository.GetGrade(id);}}
}
GradeRepository.cs
using System.Collections.Generic;
using System.Linq;namespace GraphQLDemo03_Grades
{public interface IGradeRepository{IEnumerable<Grade> GetGrades(string stuNo);Grade GetGrade(int id);}public class GradeRepository : IGradeRepository{public IEnumerable<Grade> GetGrades(string stuNo){var grades = new List<Grade>(){new Grade(1,"S0001",100,"语文"),new Grade(2,"S0001",99,"数学"),new Grade(3,"S0002",98,"语文"),new Grade(4,"S0002",97,"数学")};return grades.Where(s => s.stuNo == stuNo);}public Grade GetGrade(int id){var grades = new List<Grade>(){new Grade(1,"S0001",100,"语文"),new Grade(2,"S0001",99,"数学"),new Grade(3,"S0002",98,"语文"),new Grade(4,"S0002",97,"数学")};return grades.SingleOrDefault(s => s.ID == id);}}public record Grade(int ID, string stuNo, float score, string subject);
}最重要的是组合服务，即网关服务：GraphoQLDemo03_gateway
引入NuGet包
HotChocolate.AspNetCore
HotChocolate.Data
HotChocolate.Stitching
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;namespace GraphQLDemo03_gateway
{public class Startup{const string Students = "students";const string Grades = "grades";public void ConfigureServices(IServiceCollection services){services.AddHttpClient(Students, c => c.BaseAddress = new Uri("http://localhost:7000/graphql"));services.AddHttpClient(Grades, c => c.BaseAddress = new Uri("http://localhost:9000/graphql"));services.AddGraphQLServer().AddRemoteSchema(Students, ignoreRootTypes: true).AddRemoteSchema(Grades, ignoreRootTypes: true).AddTypeExtensionsFromString("type Query { }").AddTypeExtensionsFromFile("StudentStitching.graphql").AddTypeExtensionsFromFile("GradeStitching.graphql").AddTypeExtensionsFromFile("StudentExtendStitching.graphql").AddTypeExtensionsFromFile("GradeExtendStitching.graphql");}public void Configure(IApplicationBuilder app, IWebHostEnvironment env){if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseRouting();app.UseEndpoints(endpoints =>{endpoints.MapGraphQL();});}}
}
学生的Query类型
extend type Query{getonestudent(stuNo:String): Student @delegate(schema: "students", path:"student(stuNo:$arguments:stuNo)")getstudents: [Student] @delegate(schema: "students", path:"students")
}学生Student上扩展的属性grades集合
extend type Student{grades: [Grade] @delegate(schema: "grades", path:"grades(stuNo: $fields:stuNo)")
}
成绩的Query类型
extend type Query{getGrades(stuNo:String): [Grade] @delegate(schema: "grades", path:"grades(stuNo:$arguments:stuNo)")getGrade(id:Int!): Grade @delegate(schema: "grades", path:"grade(id:$arguments:id)")
}
成绩实体上扩展的学生student实体属性
extend type Grade{student: Student @delegate(schema: "students", path:"student(stuNo: $fields:stuNo)")
}
网关项目中通过AddHttpClient把子服务地址添加进来，再通过AddRemoteSchema把子项的架构引入进来，通过AddTypeExtensionsFromFile添加.graphql定义文件，实现类型的定义和拼接，使应用达到灵活性。
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