Efcore: Self referencing loop error

[Phylum123]

Hey guys, I found an issue with JSON, Razor Pages (Core 2) and EF (Core 2). I know all about self referencing loops and usually it can be solved with configuration. I added configuration and it did not work, I am still getting the error. Below you can see my configuration in "Startup.cs":

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {

            services.AddMvc().AddJsonOptions(options =>
            {
                options.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();
                options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Serialize;
                options.SerializerSettings.PreserveReferencesHandling = PreserveReferencesHandling.Objects;
            });

            services.AddDbContext<CapitalMarketsRMBSContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("CapitalMarketsRMBSContext")));

            //services.AddDbContext<CapitalMarketsReportsContext>(options =>
            //    options.UseSqlServer(Configuration.GetConnectionString("CapitalMarketsReportsContext")));

        }

and when I make this simple call, I get the error:

      public void OnGet()
        {
            Pool = _context.Rmbspool.Include(p => p.RmbsCertificateRates).First();
        }

Here are both entities involved in the call:

    public partial class RmbsPool: EntityBase
    {
        //*** Omitted other properties for clarity ***

                /// <summary>
        /// Child RmbsCertificateRates where [RMBSCertificateRate].[PoolId] point to this entity (FK_RMBSCertificateRate_RMBSPool)
        /// </summary>
        public virtual System.Collections.Generic.ICollection<RmbsCertificateRate> RmbsCertificateRates { get; set; } // RMBSCertificateRate.FK_RMBSCertificateRate_RMBSPool

    }

And the "Many" class:

 [Serializable]  
public partial class RmbsCertificateRate: EntityBase
    {
        //*** Omitted other properties for clarity ***
               [Required]
        [Display(Name = "Pool ID")]
        public int PoolId
        {
            get { return _poolId; }
            set { SetProperty(ref _poolId, value); }
        }

        /// <summary>
        /// Parent RmbsPool pointed by [RMBSCertificateRate].([PoolId]) FK_RMBSCertificateRate_RMBSPool)
        /// </summary>
        public virtual RmbsPool RmbsPool { get; set; } // FK_RMBSCertificateRate_RMBSPool
    }

[ralmsdeveloper]

Can you explain here the error you see?

[Phylum123]

An unhandled exception occurred while processing the request.

JsonSerializationException: Self referencing loop detected with type 'System.Collections.Generic.List`1[RMBSWeb.Main.Models.RmbsCertificateRate]'. Path 'data[0].RmbsPool'.
Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)

[ralmsdeveloper]

This does not sound like error from EF Core. But I can be wrong.
Unless you have no information in your table. and the error message is not what you want.
Try swapping First() for FirstOrDefault()

[Phylum123]

I can see the data load into the variable "Pool", but I guess when it is sending it back to the client via JSON, thats when it occurs.

[ralmsdeveloper]

If you can see the data load ... the wonderful EF Core did its part ✅

[ralmsdeveloper]

Can you attach a project to reproduce this error here?
So I could try to play, and some member of the team too.

[smitpatel]

      services.AddMvc().AddJsonOptions(options =>
            {
                options.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();
                options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Serialize;
                options.SerializerSettings.PreserveReferencesHandling = PreserveReferencesHandling.Objects;
            });

This is incorrect
ReferenceLoopHandling should be set to ignore and not serialize. See https://github.com/aspnet/EntityFrameworkCore/issues/4646#issuecomment-189152043

[Phylum123]

I tried ignore, and it didn't work