WebApi 2: JSON Serialization Exception-- self-referencing circular reference exception Solution 1: project anonymous types removing the self-referring offending property Solution 2: Use a projection into a DTO Model that does not have the self referencing property Solution 3: Use a projection into a Model Factory to create our DTO with flexibili…

FoodsController_sln1.cs

using CountingKs.Data;
using CountingKs.Data.Entities;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace CountingKs.Controllers
{
    public class FoodsController : ApiController
    {
        private ICountingKsRepository _repo;

        public FoodsController(ICountingKsRepository repo)
        {
            _repo = repo;
        }

        public IEnumerable<object> Get()
        {
            //The following code causes exception
            //
            //message: "An error has occurred."
            //exceptionMessage: "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'."
            //exceptionType: "System.InvalidOperationException"
            //stackTrace: null
            //innerException: {
            //message: "An error has occurred."
            //exceptionMessage: "Self referencing loop detected for property 'food' with type 'CountingKs.Data.Entities.Food'. Path '[0].measures[0]'."
            //exceptionType: "Newtonsoft.Json.JsonSerializationException"
            //
            //var results = _repo.GetAllFoodsWithMeasures()
            //    .OrderBy(f => f.Description)
            //    .Take(25)
            //    .ToList();

            //There are a few ways to fix this
            //Method 1: project the childe object without a reference back to the parent of the relation
            var results = _repo.GetAllFoodsWithMeasures()
                .OrderBy(f => f.Description)
                .Take(25)
                .ToList().Select(f => new{
                    Description = f.Description,
                    Measures = f.Measures.Select(m =>
                    new
                    {
                        Description = m.Description,
                        Calories = m.Calories
                    })
                });
                return results;
        }
    }
}

FoodsController_sln2.cs

using CountingKs.Data;
using CountingKs.Data.Entities;
using CountingKs.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace CountingKs.Controllers
{
    public class FoodsController : ApiController
    {
        private ICountingKsRepository _repo;

        public FoodsController(ICountingKsRepository repo)
        {
            _repo = repo;
        }

        public IEnumerable<FoodModel> Get()
        {
            //The following code causes exception
            //
            //message: "An error has occurred."
            //exceptionMessage: "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'."
            //exceptionType: "System.InvalidOperationException"
            //stackTrace: null
            //innerException: {
            //message: "An error has occurred."
            //exceptionMessage: "Self referencing loop detected for property 'food' with type 'CountingKs.Data.Entities.Food'. Path '[0].measures[0]'."
            //exceptionType: "Newtonsoft.Json.JsonSerializationException"
            //
            //var results = _repo.GetAllFoodsWithMeasures()
            //    .OrderBy(f => f.Description)
            //    .Take(25)
            //    .ToList();

            //There are a few ways to fix this
            //Method 1: project the childe object without a reference back to the parent of the relation
            //this is a fragile...
            //var results = _repo.GetAllFoodsWithMeasures()
            //    .OrderBy(f => f.Description)
            //    .Take(25)
            //    .ToList().Select(f => new{
            //        Description = f.Description,
            //        Measures = f.Measures.Select(m =>
            //        new
            //        {
            //            Description = m.Description,
            //            Calories = m.Calories
            //        })
            //    });
            //    return results;

            //Method 2 add a DTO, ViewModel that holds only what you wish to serialize to clients
            //(Automapper can help here-- See http://lostechies.com/jimmybogard/2013/08/25/automapper-3-0-released/
            var results = _repo.GetAllFoodsWithMeasures()
                .OrderBy(f => f.Description)
                .Take(25)
                .ToList().Select(f => new FoodModel
                {
                    Description = f.Description,
                    Measures = f.Measures.Select(m =>
                    new MeasureModel
                    {
                        Description = m.Description,
                        Calories = m.Calories
                    })
                });
                return results;
        }
    }
}

FoodsController_sln3.cs

using CountingKs.Data;
using CountingKs.Data.Entities;
using CountingKs.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;

namespace CountingKs.Controllers
{
    public class FoodsController : ApiController
    {
        private ICountingKsRepository _repo;
        private ModelFactory _modelFactory;

        public FoodsController(ICountingKsRepository repo)
        {
            _repo = repo;
            _modelFactory = new ModelFactory();//we intentionally did not use dependency injection
        }

        public IEnumerable<FoodModel> Get()
        {
            //The following code causes exception
            //
            //message: "An error has occurred."
            //exceptionMessage: "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'."
            //exceptionType: "System.InvalidOperationException"
            //stackTrace: null
            //innerException: {
            //message: "An error has occurred."
            //exceptionMessage: "Self referencing loop detected for property 'food' with type 'CountingKs.Data.Entities.Food'. Path '[0].measures[0]'."
            //exceptionType: "Newtonsoft.Json.JsonSerializationException"
            //
            //var results = _repo.GetAllFoodsWithMeasures()
            //    .OrderBy(f => f.Description)
            //    .Take(25)
            //    .ToList();

            //There are a few ways to fix this
            //Method 1: project the childe object without a reference back to the parent of the relation
            //this is a fragile...
            //var results = _repo.GetAllFoodsWithMeasures()
            //    .OrderBy(f => f.Description)
            //    .Take(25)
            //    .ToList().Select(f => new{
            //        Description = f.Description,
            //        Measures = f.Measures.Select(m =>
            //        new
            //        {
            //            Description = m.Description,
            //            Calories = m.Calories
            //        })
            //    });
            //    return results;

            //Method 2 add a DTO, ViewModel that holds only what you wish to serialize to clients
            //(Automapper can help here-- See http://lostechies.com/jimmybogard/2013/08/25/automapper-3-0-released/
            //var results = _repo.GetAllFoodsWithMeasures()
            //    .OrderBy(f => f.Description)
            //    .Take(25)
            //    .ToList().Select(f => new FoodModel
            //    {
            //        Description = f.Description,
            //        Measures = f.Measures.Select(m =>
            //        new MeasureModel
            //        {
            //            Description = m.Description,
            //            Calories = m.Calories
            //        })
            //    });
            //    return results;

            //Method 3:  Use a Factory Pattern to return our DTO view models
            //NOTE: WE CHOOSE NOT to use Automapper, because we want to be able to build return URI's etc into
            //to return data  e.g.  HATEOS Hypermedia etc
            //using a Model Factory, we have only one place to handling Mapping from
            //Database entities to DTO's
            var results = _repo.GetAllFoodsWithMeasures()
                .OrderBy(f => f.Description)
                .Take(25)
                .ToList().Select(f => _modelFactory.Create(f));
            return results;
        }
    }
}

self_referencing_exception.txt

{
message: "An error has occurred."
exceptionMessage: "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'."
exceptionType: "System.InvalidOperationException"
stackTrace: null
innerException: {
message: "An error has occurred."
exceptionMessage: "Self referencing loop detected for property 'food' with type 'CountingKs.Data.Entities.Food'. Path '[0].measures[0]'."
exceptionType: "Newtonsoft.Json.JsonSerializationException"