A circular reference was detected while serializin

问题:

I am trying to do a simple JSON return but I am having issues I have the following below.

public JsonResult GetEventData()
{
    var data = Event.Find(x => x.ID != 0);
    return Json(data);
}

I get a HTTP 500 with the exception as shown in the title of this question. I also tried

var data = Event.All().ToList()

That gave the same problem.

Is this a bug or my implementation?

回答1:

It seems that there are circular references in your object hierarchy which is not supported by the JSON serializer. Do you need all the columns? You could pick up only the properties you need in the view:

return Json(new 
{  
    PropertyINeed1 = data.PropertyINeed1,
    PropertyINeed2 = data.PropertyINeed2
});

This will make your JSON object lighter and easier to understand. If you have many properties, AutoMapper could be used to automatically map between DTO objects and View objects.

回答2:

I had the same problem and solved by using Newtonsoft.Json;

var list = JsonConvert.SerializeObject(model,
    Formatting.None,
    new JsonSerializerSettings() {
        ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
});

return Content(list, \"application/json\");

回答3:

This actually happens because the complex objects are what makes the resulting json object fails. And it fails because when the object is mapped it maps the children, which maps their parents, making a circular reference to occur. Json would take infinite time to serialize it, so it prevents the problem with the exception.

Entity Framework mapping also produces the same behavior, and the solution is to discard all unwanted properties.

Just expliciting the final answer, the whole code would be:

public JsonResult getJson()
{
    DataContext db = new DataContext ();

    return this.Json(
           new {
                Result = (from obj in db.Things select new {Id = obj.Id, Name = obj.Name})
               }
           , JsonRequestBehavior.AllowGet
           );
}

It could also be the following in case you don\'t want the objects inside a Result property:

public JsonResult getJson()
{
    DataContext db = new DataContext ();

    return this.Json(
           (from obj in db.Things select new {Id = obj.Id, Name = obj.Name})
           , JsonRequestBehavior.AllowGet
           );
}

回答4:

To sum things up, there are 3 solutions to this:

    private DBEntities db = new DBEntities();//dbcontext

    //Solution 1: turn off ProxyCreation for the DBContext and restore it in the end 
    public ActionResult Index()
    {
        bool proxyCreation = db.Configuration.ProxyCreationEnabled;
        try
        {
            //set ProxyCreation to false
            db.Configuration.ProxyCreationEnabled = false;

            var data = db.Products.ToList();

            return Json(data, JsonRequestBehavior.AllowGet);
        }
        catch (Exception ex)
        {
            Response.StatusCode = (int)HttpStatusCode.BadRequest;
            return Json(ex.Message);
        }
        finally
        {
            //restore ProxyCreation to its original state
            db.Configuration.ProxyCreationEnabled = proxyCreation;
        }
    }

    //Solution 2: Using JsonConvert by Setting ReferenceLoopHandling to ignore on the serializer settings. 
    //using using Newtonsoft.Json;
    public ActionResult Index()
    {
        try
        {
            var data = db.Products.ToList();

            JsonSerializerSettings jss = new JsonSerializerSettings { ReferenceLoopHandling = ReferenceLoopHandling.Ignore };
            var result = JsonConvert.SerializeObject(data, Formatting.Indented, jss);

            return Json(result, JsonRequestBehavior.AllowGet);
        }
        catch (Exception ex)
        {
            Response.StatusCode = (int)HttpStatusCode.BadRequest;
            return Json(ex.Message);
        }
    }

    //Solution 3: return a new dynamic object which includes only the needed properties.
    public ActionResult Index()
    {
        try
        {
            var data = db.Products.Select(p => new
                                                {
                                                    Product_ID = p.Product_ID,
                                                    Product_Name = p.Product_Name,
                                                    Product_Price = p.Product_Price
                                                }).ToList();

            return Json(data, JsonRequestBehavior.AllowGet);
        }
        catch (Exception ex)
        {
            Response.StatusCode = (int)HttpStatusCode.BadRequest;
            return Json(ex.Message);
        }
    }

回答5:

JSON, like xml and various other formats, is a tree-based serialization format. It won\'t love you if you have circular references in your objects, as the \"tree\" would be:

root B => child A => parent B => child A => parent B => ...

There are often ways of disabling navigation along a certain path; for example, with XmlSerializer you might mark the parent property as XmlIgnore. I don\'t know if this is possible with the json serializer in question, nor whether DatabaseColumn has suitable markers (very unlikely, as it would need to reference every serialization API)

回答6:

Its because of the new DbContext T4 template that is used for generating the EntityFramework entities. In order to be able to perform the change tracking, this templates uses the Proxy pattern, by wrapping your nice POCOs with them. This then causes the issues when serializing with the JavaScriptSerializer.

So then the 2 solutions are:

1. Either you just serialize and return the properties you need on the client

2. You may switch off the automatic generation of proxies by setting it on the context\'s configuration

   context.Configuration.ProxyCreationEnabled = false;

Very well explained in the below article.

http://juristr.com/blog/2011/08/javascriptserializer-circular-reference/

回答7:

Using Newtonsoft.Json: In your Global.asax Application_Start method add this line:

GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;

回答8:

add [JsonIgnore] to virtuals properties in your model.

回答9:

Avoid converting the table object directly. If relations are set between other tables, it might throw this error. Rather, you can create a model class, assign values to the class object and then serialize it.

回答10:

Provided answers are good, but I think they can be improved by adding an \"architectural\" perspective.

Investigation

MVC\'s Controller.Json function is doing the job, but it is very poor at providing a relevant error in this case. By using Newtonsoft.Json.JsonConvert.SerializeObject, the error specifies exactly what is the property that is triggering the circular reference. This is particularly useful when serializing more complex object hierarchies.

Proper architecture

One should never try to serialize data models (e.g. EF models), as ORM\'s navigation properties is the road to perdition when it comes to serialization. Data flow should be the following:

Database -> data models -> service models -> JSON string 

Service models can be obtained from data models using auto mappers (e.g. Automapper). While this does not guarantee lack of circular references, proper design should do it: service models should contain exactly what the service consumer requires (i.e. the properties).

In those rare cases, when the client requests a hierarchy involving the same object type on different levels, the service can create a linear structure with parent->child relationship (using just identifiers, not references).

Modern applications tend to avoid loading complex data structures at once and service models should be slim. E.g.:

1. access an event - only header data (identifier, name, date etc.) is loaded -> service model (JSON) containing only header data
2. managed attendees list - access a popup and lazy load the list -> service model (JSON) containing only the list of attendees

回答11:

I\'m Using the fix, Because Using Knockout in MVC5 views.

On action

return Json(ModelHelper.GetJsonModel<Core_User>(viewModel));

function

   public static TEntity GetJsonModel<TEntity>(TEntity Entity) where TEntity : class
    {
        TEntity Entity_ = Activator.CreateInstance(typeof(TEntity)) as TEntity;
        foreach (var item in Entity.GetType().GetProperties())
        {
            if (item.PropertyType.ToString().IndexOf(\"Generic.ICollection\") == -1 && item.PropertyType.ToString().IndexOf(\"SaymenCore.DAL.\") == -1)
                item.SetValue(Entity_, Entity.GetPropValue(item.Name));
        }
        return Entity_;  
    }

回答12:

You can notice the properties that cause the circular reference. Then you can do something like:

private Object DeCircular(Object object)
{
   // Set properties that cause the circular reference to null

   return object
}

回答13:

//first: Create a class as your view model

public class EventViewModel 
{
 public int Id{get;set}
 public string Property1{get;set;}
 public string Property2{get;set;}
}
//then from your method
[HttpGet]
public async Task<ActionResult> GetEvent()
{
 var events = await db.Event.Find(x => x.ID != 0);
 List<EventViewModel> model = events.Select(event => new EventViewModel(){
 Id = event.Id,
 Property1 = event.Property1,
 Property1 = event.Property2
}).ToList();
 return Json(new{ data = model }, JsonRequestBehavior.AllowGet);
}

回答14:

An easier alternative to solve this problem is to return an string, and format that string to json with JavaScriptSerializer.

public string GetEntityInJson()
{
   JavaScriptSerializer j = new JavaScriptSerializer();
   var entityList = dataContext.Entitites.Select(x => new { ID = x.ID, AnotherAttribute = x.AnotherAttribute });
   return j.Serialize(entityList );
}

It is important the \"Select\" part, which choose the properties you want in your view. Some object have a reference for the parent. If you do not choose the attributes, the circular reference may appear, if you just take the tables as a whole.

Do not do this:

public string GetEntityInJson()
{
   JavaScriptSerializer j = new JavaScriptSerializer();
   var entityList = dataContext.Entitites.toList();
   return j.Serialize(entityList );
}

Do this instead if you don\'t want the whole table:

public string GetEntityInJson()
{
   JavaScriptSerializer j = new JavaScriptSerializer();
   var entityList = dataContext.Entitites.Select(x => new { ID = x.ID, AnotherAttribute = x.AnotherAttribute });
   return j.Serialize(entityList );
}

This helps render a view with less data, just with the attributes you need, and makes your web run faster.