Many to Many relationship over a Web API

Question

I am trying to learn more about Entity Framework Core. Unforunately it appears to mandate a junction class when you create a many to many relationship. Please see the class structure below:

Person
Sport
PersonSport

A person has many Sports and a Sport has many Persons. When using EF I would put a Sport collection in the Person class and a Person collection in the Sport class. However, now I have to create the PersonSport class. Please see the API Controller below (this is the only code needed to replicate the problem):

namespace WebApplication1.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class PersonController : Controller
    {
        [Route("")]
        [ProducesResponseType(typeof(Person), (int)HttpStatusCode.OK)]
        //[ProducesResponseType(typeof(IEnumerable<Sport>), (int)HttpStatusCode.OK)]
        [HttpGet]
        public async Task<IActionResult> GetPerson()
        {
            Person p1 = new Person { Id = Guid.NewGuid() };
            Sport s1 = new Sport { Id = Guid.NewGuid(), Description = "Football" };
            Sport s2 = new Sport { Id = Guid.NewGuid(), Description = "Running" };
            PersonSport ps1 = new PersonSport { Person = p1, PersonId = p1.Id, Sport = s1, SportId = s1.Id };
            PersonSport ps2 = new PersonSport { Person = p1, PersonId = p1.Id, Sport = s2, SportId = s2.Id };
            List<PersonSport> personSports = new List<PersonSport>();
            personSports.Add(ps1);
            personSports.Add(ps2);
            p1.AssignSports(personSports);
            return Ok(p1);
        }
    }

    public class Entity
    {
        public Guid Id { get; set; }
    }

    public class Person : Entity
    {
        private readonly List<PersonSport> _personSports;
        public IReadOnlyCollection<PersonSport> PersonSports => _personSports.AsReadOnly();
        //public Guid Id { get; set; }

        public Person()
        {
            _personSports = new List<PersonSport>();
        }

        public void AssignSports(IEnumerable<PersonSport> personSports)
        {
            this._personSports.AddRange(personSports);
        }
    }

    public class Sport : Entity
    {
        //public Guid Id { get; set; }
        public string Description { get; set; }
    }

    public class PersonSport
    {
        public Person Person { get; set; }
        public Sport Sport { get; set; }
        public Guid PersonId { get; set; }
        public Guid SportId { get; set; }
    }
}

I debug the Web API project and navigate to: http://localhost:57320/api/Person and see this:

Notice the JSON is malformed. If I try to consume the Web API from a console app/unit test app; I see this error:

System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
   --- End of inner exception stack trace ---
   at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error)
   at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.GetResult(Int16 token)
   at System.Net.Http.HttpConnection.FillAsync()
   at System.Net.Http.HttpConnection.ChunkedEncodingReadStream.CopyToAsyncCore(Stream destination, CancellationToken cancellationToken)
   at System.Net.Http.HttpClient.GetStringAsyncCore(Task`1 getTask)
   at ConsoleApp1.Program.CallWebAPI() 

How can I resolve this? The code I am using the consume the Web API is as follows:

HttpClient enquiryClient = new HttpClient();
                var responseString = await enquiryClient.GetStringAsync("http://localhost:57320/api/Person");
                var response = JsonConvert.DeserializeObject<Person>(responseString);

Answer 1

I'll give you an example, but please note that this all would be a lot easier if you added the entity framework to your project.

To test the API, with your entities, this should work, but note: the pain lies within your entities:

public async Task<IActionResult> GetPerson()
{
    var person = new Person() {  Id = new Guid.NewGuid() };
    var sports = new [] {
                 new Sport() { Id = Guid.NewGuid(), Description = "Football" },
                 new Sport() { Id = Guid.NewGuid(), Description = "Soccer" } };

    person.AssignSports(sports);

    return Ok(person);
}

The rest of the stuff, with the virtuals, junction tables, data loading, navigation properties etc. will come when you have implemented entity framework.

For now, this will return a Person, with 2 sports.