GraphQL：拼接Stitching

2023-10-18 19:15:52

　　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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