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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

In my web API when I run project to get data from the database got this error
.net core 3.1
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.
These are my codes:
my Model
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string ProductText { get; set; }
public int ProductCategoryId { get; set; }
[JsonIgnore]
public virtual ProductCategory ProductCategory { get; set; }
}
my productCategory class is:
public class ProductCategory
{
public int Id { get; set; }
public string Name { get; set; }
public string CatText { get; set; }
public string ImagePath { get; set; }
public int Priority { get; set; }
public int Viewd { get; set; }
public string Description { get; set; }
public bool Active { get; set; }
public DateTime CreateDate { get; set; }
public DateTime ModifyDate { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
my repo is
public async Task<IList<Product>> GetAllProductAsync()
{
return await _context.Products.Include(p => p.ProductCategory).ToListAsync();
}
my interface
public interface IProductRepository
{
...
Task<IList<Product>> GetAllProductAsync();
...
}
and this is my controller in api project
[Route("api/[controller]")]
[ApiController]
public class ProductsController : ControllerBase
{
private readonly IProductRepository _productRepository;
public ProductsController(IProductRepository productRepository)
{
_productRepository = productRepository;
}
[HttpGet]
public ActionResult Get()
{
return Ok(_productRepository.GetAllProduct());
}
}
When I run API project and put this URL: https://localhost:44397/api/products
I got that error,
I can't resolve it

this is happening because your data have a reference loop.
e.g
// this example creates a reference loop
var p = new Product()
{
ProductCategory = new ProductCategory()
{ products = new List<Product>() }
};
p.ProductCategory.products.Add(p); // <- this create the loop
var x = JsonSerializer.Serialize(p); // A possible object cycle was detected ...
You can not handle the reference loop situation in the new System.Text.Json yet (netcore 3.1.1) unless you completely ignore a reference and its not a good idea always. (using [JsonIgnore] attribute)
but you have two options to fix this.
you can use Newtonsoft.Json in your project instead of System.Text.Json (i linked an article for you)
Download the System.Text.Json preview package version 5.0.0-alpha.1.20071.1 from dotnet5 gallery (through Visual Studio's NuGet client):
option 1 usage:
services.AddMvc()
.AddNewtonsoftJson(
options => {
options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
});
// if you not using .AddMvc use these methods instead
//services.AddControllers().AddNewtonsoftJson(...);
//services.AddControllersWithViews().AddNewtonsoftJson(...);
//services.AddRazorPages().AddNewtonsoftJson(...);
option 2 usage:
// for manual serializer
var options = new JsonSerializerOptions
{
ReferenceHandling = ReferenceHandling.Preserve
};
string json = JsonSerializer.Serialize(objectWithLoops, options);
// -----------------------------------------
// for asp.net core 3.1 (globaly)
services.AddMvc()
.AddJsonOptions(o => {
o.JsonSerializerOptions
.ReferenceHandling = ReferenceHandling.Preserve
});
these serializers have ReferenceLoopHandling feature.
Edit : ReferenceHandling changed to ReferenceHandler in DotNet 5
but if you decide to just ignore one reference use [JsonIgnore] on one of these properties. but it causes null result on your API response for that field even when you don't have a reference loop.
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string ProductText { get; set; }
public int ProductCategoryId { get; set; }
// [JsonIgnore] HERE or
public virtual ProductCategory ProductCategory { get; set; }
}
public class ProductCategory
{
public int Id { get; set; }
// [JsonIgnore] or HERE
public ICollection<Product> products {get;set;}
}

.NET 5 Web API
public static void ConfigureServices(this IServiceCollection services, IConfiguration configuration)
{
services.AddControllers()
.AddJsonOptions(o => o.JsonSerializerOptions
.ReferenceHandler = ReferenceHandler.Preserve);
}

I have the same issue, my fix was to add async and await keyword since I am calling an async method on my business logic.
Here is my original code:
[HttpGet]
public IActionResult Get()
{
//This is async method and I am not using await and async feature .NET which triggers the error
var results = _repository.GetAllDataAsync();
return Ok(results);
}
To this one:
HttpGet]
public async Task<IActionResult> Get()
{
var results = await _repository.GetAllDataAsync();
return Ok(results);
}

In .Net 6, you can use System.Text.Json to initialize a startup action with AddControllersWithViews like this in Program.cs,
using System.Text.Json.Serialization;
builder.Services.AddControllersWithViews()
.AddJsonOptions(x => x.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles);
also you can use AddMvc like this,
builder.Services.AddMvc()
.AddJsonOptions(x => x.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles);
but quote from Ryan
asp.net core 3.0+ template use these new
methodsAddControllersWithViews,AddRazorPages,AddControllers instead of
AddMvc.
I will recommend to use the first solution.

Ensure you have [JsonIgnore] on the correct fields to avoid a circular reference.
In this case you will need
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string ProductText { get; set; }
[JsonIgnore]
public virtual ProductCategory ProductCategory { get; set; }
}
You probably don't need the ProductCategoryId field (depends if you are using EF and code first to define your DB)
Edit - In answer to noruk
There is often confusion in connected objects and navigation properties. You can get the data you want in JSON but also define the EF structures to get the correct DB structure (foreign keys, indexes, etc).
Take this simple example. A Product (for example a T-Shirt) has many sizes or SKUs (e.g. Small, Large, etc)
public class Product
{
[Key]
[MaxLength(50)]
public string Style { get; set; }
[MaxLength(255)]
public string Description { get; set; }
public List<Sku> Skus { get; set; }
}
public class Sku
{
[Key]
[MaxLength(50)]
public string Sku { get; set; }
[MaxLength(50)]
public string Barcode { get; set; }
public string Size { get; set; }
public decimal Price { get; set; }
// One to Many for Product
[JsonIgnore]
public Product Product { get; set; }
}
Here you can serialise a Product and the JSON data will include the SKUs. This is the normal way of doing things.
However if you serialise a SKU you will NOT get it's parent product. Including the navigation property will send you into the dreaded loop and throw the "object cycle was detected" error.
I know this is limiting in some use cases but I would suggest you follow this pattern and if you want the parent object available you fetch it separately based on the child.
var parent = dbContext.SKUs.Include(p => p.Product).First(s => s.Sku == "MY SKU").Product

I fixed my API Core Net6.0 adding [JsonIgnore]:
public class SubCategoryDto
{
public int Id { get; set; }
public string Name { get; set; }
public string Image { get; set; }
public int CategoryId { get; set; }
[JsonIgnore]
public Category Category { get; set; }
}

For net core 3.1 you have to add in Startup.cs:
services.AddMvc.AddJsonOptions(o => {
o.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.Preserve;
o.JsonSerializerOptions.MaxDepth = 0;
})
and import at least this package using nuget.org include prerelease:
<PackageReference Include="System.Text.Json" Version="5.0.0-rc.1.20451.14" />

following code is working for me in dotnet 5.0 :
services.AddControllersWithViews()
.AddJsonOptions(o => o.JsonSerializerOptions
.ReferenceHandler = ReferenceHandler.Preserve);

Finally fixed mine with System.Text.Json not NewtonSoft.Json using
var options = new JsonSerializerOptions()
{
MaxDepth = 0,
IgnoreNullValues = true,
IgnoreReadOnlyProperties = true
};
Using options to serialize
objstr = JsonSerializer.Serialize(obj,options);

My project built with a similar error.
Here's the code before
public class PrimaryClass {
public int PrimaryClassId
public ICollection<DependentClass> DependentClasses { get; set; }
}
public class DependentClass {
public int DependentClassId { get; set; }
public int PrimaryClassId { get; set; }
public PrimaryClass primaryClass { get; set; }
}
I took away the PrimaryClass object from the DependentClass model.
Code after
public class PrimaryClass {
public int PrimaryClassId
public ICollection<DependentClass> DependentClasses { get; set; }
}
public class DependentClass {
public int DependentClassId { get; set; }
public int PrimaryClassId { get; set; }
}
I also had to adjust the OnModelCreating method from
modelBuilder.Entity<PrimaryClass>().HasMany(p => p.DependentClasses).WithOne(d => d.primaryClass).HasForeignKey(d => d.PrimaryClassId);
to
modelBuilder.Entity<PrimaryClass>().HasMany(p => p.DependentClasses);
The DbSet query that's running is
public async Task<List<DependentClass>> GetPrimaryClassDependentClasses(PrimaryClass p)
{
return await _dbContext.DependentClass.Where(dep => dep.PrimaryClassId == p.PrimaryClassId).ToListAsync();
}
The error could have been with any of these 3 sections of code, but removing the primary object reference from the dependent class and adjusting the OnModelCreating resolved the error, I'm just not sure why that would cause a cycle.

In my case the problem was when creating the entity relationships. I linked the main entity using a foreign key inside the dependent entity like this
[ForeignKey("category_id")]
public Device_Category Device_Category { get; set; }
also I referred the dipendend entity inside the main entity as well.
public List<Device> devices { get; set; }
which created a cycle.
Dependent Entity
public class Device
{
[Key]
public int id { get; set; }
public int asset_number { get; set; }
public string brand { get; set; }
public string model_name { get; set; }
public string model_no { get; set; }
public string serial_no { get; set; }
public string os { get; set; }
public string os_version { get; set; }
public string note { get; set; }
public bool shared { get; set; }
public int week_limit { get; set; }
public bool auto_acceptance { get; set; }
public bool booking_availability { get; set; }
public bool hide_device { get; set; }
public bool last_booked_id { get; set; }
//getting the relationships category 1 to many
public int category_id { get; set; }
[ForeignKey("category_id")]
public Device_Category Device_Category { get; set; }
public List<Booking> Bookings { get; set; }
}
Main Entity
public class Device_Category
{
public int id { get; set; }
public string name { get; set; }
public List<Device> devices { get; set; }
}
}
So I commented the
public List<Device> devices { get; set; }
inside main entity (Device_Category) and problem solved

nested json deserialization - need another set of eyes

I have been trying to get this json to deserialize for two days now using RestSharp. I have gone through the RestSharp github site, looked at countless examples, and spent much time here on Stack Overflow to try and find the answer to no avail. My code had previously worked perfectly but the vendor changed their API version and I was forced to do an update to keep using the application for my legal practice. My json is as follows(client info has been removed and replaced with generic info):
{
"data":[
{
"id":1035117666,
"client":
{
"id":905422394,
"name":"client1"
},
"display_number":"11-00012",
"description":"General",
"practice_area":
{
"id":4269978,
"name":"Business"
},
"status":"Open",
"open_date":"2011-12-14",
"close_date":null,
"billing_method":"hourly"
},
{
"id":1035117768,
"client":
{
"id":905422506,
"name":"client2"
},
"display_number":"12-00037",
"description":"HOA",
"practice_area":
{
"id":4269978,
"name":"Business"
},
"status":"Open",
"open_date":"2012-08-07",
"close_date":null,
"billing_method":"hourly"
}
],
"meta":
{
"paging":
{
"next":"https://app.goclio.com/api/v4/matters.json?fields=id%2C+client%7Bid%2C+name%7D%2C+display_number%2C+description%2C+practice_area%7Bid%2C+name%7D%2C+status%2C+open_date%2C+close_date%2C+billing_method&limit=2&page_token=BAh7BjoLb2Zmc2V0aQc%3D--b1ea3eba20c8acefbcdfc7868debd1e0ee630c64&status=Open"
},
"records":91
}
}
I built the following schema within my c# code:
public class MatterList
{
public List<Matter> matters { get; set; }
public Meta meta { get; set; }
}
public class Meta
{
public Paging paging { get; set; }
public int records { get; set; }
}
public class Paging
{
public string previous { get; set; }
public string next { get; set; }
}
[DeserializeAs(Name = "data")]
public class Matter
{
public int id { get; set; }
public Client client { get; set; }
public string display_number { get; set; }
public string description { get; set; }
public PracticeArea practice_area { get; set; }
public string status { get; set; }
public DateTime open_date { get; set; }
public DateTime close_date { get; set; }
public string billing_method { get; set; }
public string type = "matter";
}
public class PracticeArea
{
public int id { get; set; }
public string name { get; set; }
}
public class Client
{
public int id { get; set; }
public string name { get; set; }
}
When I run the RestSharp deserialize method I am sending the result to an object of type MatterList using the following line of code
MatterList matterList = jsonHandler.Deserialize<MatterList>(response);
I have so far attempted to deserialize without the Meta or Paging POCO classes with the accompanying change to the MatterList class (taking out the Meta property).
I have tried with and without the [DeserializeAs(Name="data")] directive.
I have tried to set the RootElement of the json response prior to deserialization.
I have tried to shorthand the deserialization by combining it with the Execute request code
IRestResponse<MatterList> matterList = client.Execute<MatterList>(request);
I have created a container class called MatterContainer which I placed between MatterList and Matter classes in the schema:
public class MatterList
{
public List<MatterContainer> matters { get; set; }
}
public class MatterContainer
{
public Matter matter { get; set; }
}
public class Matter
{
public int id { get; set; }
public Client client { get; set; }
public string display_number { get; set; }
public string description { get; set; }
public PracticeArea practice_area { get; set; }
public string status { get; set; }
public DateTime open_date { get; set; }
public DateTime close_date { get; set; }
public string billing_method { get; set; }
public string type = "matter";
}
I know I am getting the json response back from the server correctly so my request is proper and MatterList is not null after deserialization. The problem is that I cannot get the deserialization to actually populate the List matters within the MatterList class.
I have been looking at this off and on for two days and cannot get past this hurdle. If anyone sees what I did wrong I would greatly appreciate the insight, I am at a point where I cannot progress further with my application.
Thanks!

I think your [DeserializeAs(Name = "data")] attribute is in the wrong place. Try putting it in the root class instead:
public class MatterList
{
[DeserializeAs(Name = "data")]
public List<Matter> matters { get; set; }
public Meta meta { get; set; }
}
alternatively, try renameing that property to data

Web api skips all objects but first in List<T> when returning to client

I have a web api that returns a complex object that looks like this:
public class CanDeleteRumsaAttributeResponse
{
public CanDeleteRumsaAttributeResponse()
{
}
public CanDeleteRumsaAttributeResponse(int attributeId)
{
RumsaAttributeId = attributeId;
}
public int RumsaAttributeId { get; set; }
public bool AttributeFound { get; set; }
public List<RumsaRoom> AffectedRumsaRooms { get; set; } = new List<RumsaRoom>();
public List<RumsaAttribute> AffectedLinkedRumsaAttributes { get; set; } = new List<RumsaAttribute>();
[JsonIgnore]
public bool CanDelete
{
get
{
return AffectedRumsaRooms.Count == 0&&AttributeFound&&AffectedLinkedRumsaAttributes.Count==0;
}
}
}
When I debug it I can see that the controller return that object and that the list AffectedLinkedRumsaAttributes has several objects in the list
When the client receives the list all but the first object are null.
I've tried returning the object as Ok(CanDeleteRumsaAttributeResponse) and I've tried serializing it like this:
RoomAttributesUtils utils = new RoomAttributesUtils(db);
string json = JsonConvert.SerializeObject(utils.GetCanDeleteColor(id));
var response = this.Request.CreateResponse(HttpStatusCode.OK);
response.Content = new StringContent(json, Encoding.UTF8, "application/json");
return response;
In the second case I can search the json string and find the missing data.
So its being serialized in the second case.
I've checked fiddler to see what is being sent and I can see that something is not right in the json-data.
The missing objects gets values like $ref: "4" and so on, but nothing else.
Here is the json-string I'm afraid I dont know how to format it properly for Stackoverflow, but I think that the information is there as well, but when I look at it using a viewer, its not and it sure doesnt deserialize to the correct objects.
The other list in the object can have any number of objects and they all return fine. Also, other endpoints are returning lists of the same type perfectly fine.
The three objects have unique values on the Code property and they are V30, V31 and V12 (if you want to identify them in the json string).
Any ideas?
Here is the json string
{"RumsaAttributeId":4797,"AttributeFound":true,"AffectedRumsaRooms":[{"$id":"1","RoomName":"STÄD","RoomNumber":"U12102-1150","Building":"U1","PartOfBuilding":"21","Plan":"02","Number":"1150","RoomDescriptions":[],"IsDeleted":false,"PMs":[],"IDNR":"175D_40","Exclude":false,"Department":"VN40 Lokalvård","Comments":"","Area":"23.19","HygeneClass":null,"CeilingHeight":"","UniqueRoomId":"d00e5325-7918-4d01-b273-813a770b46ca-010591d3","SolviegHasOpenedThis":true,"LastSynchedFromRevit":"1900-01-01T00:00:00","LastUpdatedFromRevit":"1900-01-01T00:00:00","Id":25772}],"AffectedLinkedRumsaAttributes":[{"$id":"2","AMACode":"KBC.3211","Malning":"56-03510","AvaliableColors":[{"$id":"3","AvaliableMaterials":[{"$ref":"2"},{"$id":"4","AMACode":"MBE.221","Malning":"-","AvaliableColors":[{"$ref":"3"}],"RoomDescriptions":[],"Code":"V30","ShortDescription":"Kakel, vattenavvisande beklädnad","LongDescription":"-","Comment":"-","PartOfRoom":null,"PartOfRoomId":960,"Id":1438},{"$id":"5","AMACode":"MBE.222","Malning":"-","AvaliableColors":[{"$ref":"3"}],"RoomDescriptions":[],"Code":"V31","ShortDescription":"Kakel, vattentät beklädnad","LongDescription":"-","Comment":"-","PartOfRoom":null,"PartOfRoomId":960,"Id":1439}],"RoomDescriptions":[],"Code":"V31_01","ShortDescription":"Kakel, vattentät beklädnad","LongDescription":"Marazzi SistemC Arch ME83, kulör Bianco(vit)200x200x5 mm. Fog Mapei Ultracolor Plus kulör 111 Silver Grey","Comment":"På 1 fondvägg","PartOfRoom":null,"PartOfRoomId":960,"Id":4797}],"RoomDescriptions":[],"Code":"V12","ShortDescription":"Gipsskivor, hygienklass 2","LongDescription":"Hög standard, hygienklass 2\n","Comment":"-","PartOfRoom":null,"PartOfRoomId":960,"Id":1425},{"$ref":"4"},{"$ref":"5"}]}

I had a similar situation in which I found that due to circular references, the serialization was not completed.
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
public List<Post> Posts { get; set; }
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogForeignKey { get; set; }
[ForeignKey("BlogForeignKey")]
public Blog Blog {get;set;}
}
I just deleted the child to parent relationship and included the foreingkey anotation to the entity set.
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
[ForeignKey("BlogForeignKey")]
public List<Post> Posts { get; set; }
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogForeignKey { get; set; }
}
Also consider LoopReferenceHandling

Mobile Azure Service C# .NET Backend PATCH not updating

I've created a simple .NET backend mobile azure service in C#. I have the mobile service up and running (all it's doing currently is working with your normal CRUD on a single table). The problem I'm having is that the PATCH/UPDATE will not do as it says. I can do everything else I've tried, SELECT, INSERT, DELETE, but I've been unable to update data.
When I debug into the block of code that calls UpdateAsync, the patch.GetEntity()..... always has the values NULL or zeroed out or day one datetimes, like it's not passing along the property values of what I'm trying to update. The only value I ever have is the correct id. Below I tried to strip out some of the code I have, I used some of what was in the first few tutorials on the Azure website.
I have a Data Object:
public class AdminLookupDATA: EntityData
{
public string description { get; set; }
public int lookuptype { get; set; }
public int priority { get; set; }
public bool inactive { get; set; }
public DateTime createdate { get; set; }
public DateTime editdate { get; set; }
}
I have a DTO:
public class AdminLookupDTO
{
public string id { get; set; }
public string description { get; set; }
public int lookuptype { get; set; }
public int priority { get; set; }
public bool inactive { get; set; }
public DateTime createdate { get; set; }
public DateTime editdate { get; set; }
}
I have a Model:
public class AdminLookupModel
{
public string Id { get; set; }
public string description { get; set; }
public int lookuptype { get; set; }
public int priority { get; set; }
public bool inactive { get; set; }
public DateTime createdate { get; set; }
public DateTime editdate { get; set; }
}
My PATCH inside my controller:
public Task<AdminLookupDATA> PatchAdminLookupDATA(string id, Delta<AdminLookupDATA> patch)
{
return UpdateAsync(id, patch);
}
Also, I have the same issue if I try to run the PATCH function directly from the browser in the "try it out" section, so it's something I have configured wrong within the service project itself. Any suggestions would be greatly appreciated.
Thanks,
Rob

Your property names must start with a capital letter.
Otherwise configure the CamelCasePropertyNamesContractResolver as indicated here:
http://odetocode.com/blogs/scott/archive/2013/03/25/asp-net-webapi-tip-3-camelcasing-json.aspx
code snippet
var formatters = GlobalConfiguration.Configuration.Formatters;
var jsonFormatter = formatters.JsonFormatter;
var settings = jsonFormatter.SerializerSettings;
settings.Formatting = Formatting.Indented;
settings.ContractResolver = new CamelCasePropertyNamesContractResolver();

Updating List<T> in DbContext

I have a Model like this
public class Challenge
{
public int ID { get; set; }
public string Name { get; set; }
public string Blurb { get; set; }
public int Points { get; set; }
public string Category { get; set; }
public string Flag { get; set; }
public List<string> SolvedBy { get; set; }
}
public class ChallengeDBContext : DbContext
{
public DbSet<Challenge> Challenges { get; set; }
}
and then Controller like this. But I cannot update the List "SolvedBy", the next time I step through with the debugger, the list is still empty.
[HttpPost]
public string Index(string flag = "", int id=0)
{
Challenge challenge = db.Challenges.Find(id);
if (flag == challenge.Flag)
{
var chall = db.Challenges.Find(id);
if (chall.SolvedBy == null)
{
chall.SolvedBy = new List<string>();
}
chall.SolvedBy.Add(User.Identity.Name);
db.Entry(chall).State = EntityState.Modified;
db.SaveChanges();
//congrats, you solved the puzzle
return "got it";
}
else
{
return "fail";
}
}
is there any way around it to make a list of strings kept in the database?

EF don't know how to store an array in database table so it just ignore it. You can create another table/entity or use XML/JSON to store the list. You can serialize the list before saving and deserialize it after loading from database

A List<T> in a model would normally map to a second table, but in your DbContext you only have a single table. Try adding a second table.
public class ChallengeDBContext : DbContext
{
public DbSet<Challenge> Challenges { get; set; }
public DbSet<Solution> Solutions {get; set;}
}
public class Challenge
{
public int ID { get; set; }
public string Name { get; set; }
public string Blurb { get; set; }
public int Points { get; set; }
public string Category { get; set; }
public string Flag { get; set; }
public List<Solution> SolvedBy { get; set; }
}
public class Solution
{
public int ID { get; set; }
public string Name { get; set; }
}
Then your controller can use code along the lines of...
var chall = db.Challenges.Find(id);
if (chall.SolvedBy == null)
{
chall.SolvedBy = new List<Solution>();
}
chall.SolvedBy.Add(new Solution {Name=User.Identity.Name});
None of the above has been tested and I may have made some mistakes there, but the general principle I want to illustrate is the fact that you need another table. The List<T> represents a JOIN in SQL.