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？

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.EntityFrameworkCore
Pomelo.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 employeeApplications
return _context.Employees.Include(e => e.EmployeeApplications); //returns employees and their employeeApplications,but the applications of employeeApplications is empty
return _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
}

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？

解决方法

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