.Net Core 3.0 possible object cycle was detected which is not supported

问题

I have 2 entities that are related as one to many

public class Restaurant {
   public int RestaurantId {get;set;}
   public string Name {get;set;}
   public List<Reservation> Reservations {get;set;}
   ...
}

public class Reservation{
   public int ReservationId {get;set;}
   public int RestaurantId {get;set;}
   public Restaurant Restaurant {get;set;}
}

If I try to get restaurants with reservations using my api

   var restaurants =  await _dbContext.Restaurants
                .AsNoTracking()
                .AsQueryable()
                .Include(m => m.Reservations).ToListAsync();
    .....

I receive error in response, because objects contain references to each other. There are related posts that recommend to create separate model or add NewtonsoftJson configuration

Problem is that I do not want to create separate model and 2nd suggestion didn't help. Is there any way to load data without cycled relationship ? *

System.Text.Json.JsonException: A possible object cycle was detected which is not supported. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32. at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_SerializerCycleDetected(Int32 maxDepth) at System.Text.Json.JsonSerializer.Write(Utf8JsonWriter writer, Int32 originalWriterDepth, Int32 flushThreshold, JsonSerializerOptions options, WriteStack& state) at System.Text.Json.JsonSerializer.WriteAsyncCore(Stream utf8Json, Object value, Type inputType, JsonSerializerOptions options, CancellationToken cancellationToken) at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding) at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()

*

回答1:

I have tried your code in a new project and the second way seems to work well after installing the package Microsoft.AspNetCore.Mvc.NewtonsoftJson firstly for 3.0

services.AddControllersWithViews()
    .AddNewtonsoftJson(options =>
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
);

Try with a new project and compare the differences.

回答2:

.NET Core 3.1 Install the package Microsoft.AspNetCore.Mvc.NewtonsoftJson

Startup.cs Add service

services.AddControllers().AddNewtonsoftJson(options =>
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
);

回答3:

Getting the setting JSON serialisation options on startup to work is probably a preferred way as you will likely have similar cases in the future. In the meantime however you could try add data attributes to your model so it's not serialised: https://www.newtonsoft.com/json/help/html/PropertyJsonIgnore.htm

public class Reservation{ 
    public int ReservationId {get;set;} 
    public int RestaurantId {get;set;} 
    [JsonIgnore]
    public Restaurant Restaurant {get;set;} 
}

回答4:

public class Reservation{ 
public int ReservationId {get;set;} 
public int RestaurantId {get;set;} 
[JsonIgnore]
public Restaurant Restaurant {get;set;} 

Above worked also. But I prefer the following

services.AddControllers().AddNewtonsoftJson(options =>
    options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
);

Because first we need to add the attribute to all the models we may have the cyclic reference.

来源：https://stackoverflow.com/questions/59199593/net-core-3-0-possible-object-cycle-was-detected-which-is-not-supported