如何从具有多对多关系的C#Web API Visual Studio 2017 RTM提供(GET)复杂(嵌套)JSON？

概述我很久以来一直坚持这个问题. 我的环境： > Visual Studio 2017 RTM(使用此IDE的默认.net核心版本) > Web API > ASP.NET核心1.1 > MySQL通过Pomelo数据库提供商 我安装的包： Microsoft.EntityFrameworkCorePomelo.EntityFrameworkCore.MySql Microsoft.EntityF 我很久以来一直坚持这个问题.

我的环境：

> Visual Studio 2017 RTM(使用此IDE的默认.net核心版本)
> Web API
> ASP.NET核心1.1
> MySQL通过Pomelo数据库提供商

我安装的包：

Microsoft.EntityFrameworkCorePomelo.EntityFrameworkCore.MysqL Microsoft.EntityFrameworkCore.Tools

我首先使用代码创建了3个表.

>员工：有员工名单
>申请：申请表
> EmployeeApplications：Employees和Applications的Join表

Employee和Application具有M：M关系,因此我在它们之间创建了连接表.

员工模型：

using System;using System.Collections.Generic;using System.linq;using System.Threading.Tasks;using System.ComponentModel.DataAnnotations;namespace Test.Models{    public class Employee    {        public int EmployeeID { get; set; }        [required]        public string Lname { get; set; }        [required]        public string Fname { get; set; }        public string Title { get; set; }        //Navigation Property        public ICollection<EmployeeApplications> EmployeeApplications { get; set; }    }}

应用模型：

using System.linq;using System.Threading.Tasks;using System.ComponentModel.DataAnnotations;namespace Teset.Models{    public class Application    {        public int ApplicationID { get; set; }        [required]        public string name { get; set; }        public string Description { get; set; }        //Navigation Property        public ICollection<EmployeeApplications> EmployeeApplications { get; set; }    }}

员工应用模型：

using System;using System.Collections.Generic;using System.linq;using System.Threading.Tasks;namespace Test.Models{    public class EmployeeApplications    {        public int EmployeeID { get; set; }        public int ApplicationID { get; set; }        public Employee Employee { get; set; }        public Application Application { get; set; }    }}

员工控制员：

[Produces("application/Json")][Route("API/Employees")]public class EmployeesController : Controller{    private Readonly TestContext _context;    public EmployeesController(TestContext context)    {        _context = context;    }    // GET: API/Employees    [httpGet]    public IEnumerable<Employee> GetEmployees()    {        return _context.Employees;    }

语境：

using Test.Models;using Microsoft.EntityFrameworkCore;namespace Test.Data{    public class TestContext : DbContext    {        public TestContext(DbContextoptions<TestContext> options) : base(options)        {        }        public DbSet<Employee> Employees { get; set; }        public DbSet<Application> Applications { get; set; }        public DbSet<EmployeeApplications> EmployeeApplications { get; set; }        protected overrIDe voID OnModelCreating(ModelBuilder modelBuilder)        {            modelBuilder.Entity<EmployeeApplications>()                .HasKey(c => new { c.EmployeeID,c.ApplicationID });        }    }}

我尝试过使用.Include().当我跑去API / Employees时,我得到Postman的“无法得到任何回应”.

return _context.Employees.Include(e => e.EmployeeApplications);

我已经尝试了很多变化,但仍然没有运气.包含.Include()的任何变体都会失败.

电流输出样本：

[{    "employeeID": 1,"lname": "Doe","fname": "John","Title": "Senior Software Engineer","employeeApplications": null},{    "employeeID": 2,"lname": "Smith","fname": "Jack","Title": "Project Manager","employeeApplications": null}]

我尝试使用DTO并取得了一些成功.我设法用employeeApplications中的内容替换上面的null,但是后来对Employee和Applications有了null引用.

我理想的输出：

[{    "employeeID": 1,"employeeApplications": [{        "applicationID": 1,"name": "Application 1","description": "Description 1",},{        "applicationID": 2,"name": "Application 2","description": "Description 2",}]},"employeeApplications": [{        "applicationID": 2,{        "applicationID": 3,"name": "Application 3","description": "Description 3",}]}]

基本上我想提供一份“员工”列表和他们所使用的应用程序.稍后我还要提供一份应用程序列表和处理它们的员工.

编辑：上面添加了上下文文件

编辑2：我遵循Bchir Med Amine的解决方案(目前没有工作),但后来我添加到Startup.cs的ConfigureServices方法：

services.AddMvc()                .AddJsonoptions(                    options => options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore                );

这让我获得了有关我的JsON的更多信息,但仍未完整. JsON现在看起来像这样：

[{    "employeeID": 1,"employeeApplications": [{        "employeeID": 1,"applicationID": 1,"application": null    },{        "employeeID": 1,"applicationID": 2,"application": null    }]},"employeeApplications": [{        "employeeID": 2,{        "employeeID": 2,"applicationID": 3,"application": null    }]}]

应用程序现在为null.我不得不使用.Include()来生成它,但是在包含应用程序之后使用.ThenInclude()不起作用.理想的情况是打印出所有员工的清单,每个员工都应该有一份申请清单.

编辑3：我错了.ThenInclude()没有工作,是Intelisense让我失望.如果我使用.ThenInclud()我得到这个JsON：

[{    "employeeID": 1,"application": {            "applicationID": 1,"employeeApplications": []        }    },"application": {            "applicationID": 2,"employeeApplications": []        }    }]},"employeeApplications": [{                "employeeID": 1,"employee": {                    "employeeID": 1,"employeeApplications": [{                        "employeeID": 1,"application": {                            "applicationID": 1,"employeeApplications": []                        }                    }]                }            }]        }    },"application": {            "applicationID": 3,"employeeApplications": []        }    }]}]

第一个员工对象是Ok(仍然不理想,但它可以工作),但第二个员工不是.第二个打印出员工的应用程序,然后打印出这些应用程序的员工.

编辑4：以下是我返回JsON的方式：

return _context.Employees; //Returns just employees and '[]' for employeeApplicationsreturn _context.Employees.Include(e => e.EmployeeApplications); //returns employees and their employeeApplications,but the applications of employeeApplications is emptyreturn _context.Employees.Include(e => e.EmployeeApplications).ThenInclude(ea => ea.Application); //returns everything,but continues due to circular reference

解决方法 也许你必须将Virtual添加到类中

public class Application{    #region Public Constructors    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2214:DoNotCalloverrIDableMethodsInConstructors")]    public Application()    {        EmployeeApplications = new HashSet<EmployeeApplications>();    }    #endregion Public Constructors    #region Public PropertIEs    public int ApplicationID { get; set; }    public string Description { get; set; }    //Navigation Property    public virtual ICollection<EmployeeApplications> EmployeeApplications { get; set; }    [required]    public string name { get; set; }    #endregion Public PropertIEs}public class Employee{    #region Public Constructors    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage","CA2214:DoNotCalloverrIDableMethodsInConstructors")]    public Employee()    {        EmployeeApplications = new HashSet<EmployeeApplications>();    }    #endregion Public Constructors    #region Public PropertIEs    //Navigation Property    public virtual ICollection<EmployeeApplications> EmployeeApplications { get; set; }    public int EmployeeID { get; set; }    [required]    public string Fname { get; set; }    [required]    public string Lname { get; set; }    public string Title { get; set; }    #endregion Public PropertIEs}public class EmployeeApplications{    #region Public PropertIEs    public virtual Application Application { get; set; }    public int ApplicationID { get; set; }    public virtual Employee Employee { get; set; }    public int EmployeeID { get; set; }    #endregion Public PropertIEs}

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