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?
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.
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");
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
);
}
To sum things up, there are 4 solutions to this:
Solution 1: turn off ProxyCreation for the DBContext and restore it in the end.
private DBEntities db = new DBEntities();//dbcontext
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;
private DBEntities db = new DBEntities();//dbcontext
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);
}
}
Following two solutions are the same, but using a model is better because it's strong typed.
Solution 3: return a Model which includes the needed properties only.
private DBEntities db = new DBEntities();//dbcontext
public class ProductModel
{
public int Product_ID { get; set;}
public string Product_Name { get; set;}
public double Product_Price { get; set;}
}
public ActionResult Index()
{
try
{
var data = db.Products.Select(p => new ProductModel
{
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);
}
}
Solution 4: return a new dynamic object which includes the needed properties only.
private DBEntities db = new DBEntities();//dbcontext
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);
}
}
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)
add [JsonIgnore] to virtuals properties in your model.
Using Newtonsoft.Json: In your Global.asax Application_Start method add this line:
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
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:
Either you just serialize and return the properties you need on the client
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/
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.:
access an event - only header data (identifier, name, date etc.) is loaded -> service model (JSON) containing only header data
managed attendees list - access a popup and lazy load the list -> service model (JSON) containing only the list of attendees
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.
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_;
}
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
}
//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);
}
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.
Currently I have an IActionFilter that accepts a List<T> as parameter. In that action method I examine the posted viewmodel values. It looks something like this:
[HttpPost]
public async Task<IActionResult> SavePage(List<BaseField> fields)
{
for (var i = 0; i < fields.Count; i++)
{
if (fields[i].Type == "bb")
{
var inputObj = new InputConfigViewModel();
await TryUpdateModelAsync(inputObj, $"fields[{i}]");
}
if (fields[i].Type == "ee")
{
var tObj = new TextareaConfigViewModel();
await TryUpdateModelAsync(tObj, $"fields[{i}]");
}
}
return RedirectToAction("Index", "Dashboard");
}
This works so far. But I would like to abstract this code away to a custom ModelBinder class.
public class BaseFieldModelBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
// Need access to "List<BaseField> fields"...
return Task.CompletedTask;
}
}
How can I get access the List<BaseField> fields values in my ModelBinder, like I can from the action method in my Controller?
Custom model binders work on objects and not generic lists. You cannot access the all list inside the binder, but you can access each individual object.
With this said, I don't believe you can abstract the code, because you don't have the ControllerContext you need to access the FormCollection inside the binder context, neither to execute the TryUpdateModelAsync call in order to get extra information from form post that is not present on the List<BaseField>. You just have the ModelBindingContext.
If you still want to try, you have a good working example here.
Here is the relevant part, where you can get the reference of the object:
// Try to fetch the value of the argument by name
var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName);
if (valueProviderResult == ValueProviderResult.None)
{
return TaskCache.CompletedTask;
}
bindingContext.ModelState.SetModelValue(modelName, valueProviderResult);
var value = valueProviderResult.FirstValue;
// Check if the argument value is null or empty
if (string.IsNullOrEmpty(value))
{
return TaskCache.CompletedTask;
}
I'm working with ASP.Net MVC4, I customize my login, this is ok, I would like save this object USER and I can access from differents controllers and differents Areas. I was trying to defined this object as "static" but I can't acces to values of object:
if (Servicio.ValidarUsuario())
{
string Mensaje = "";
Models.AdmUsuario oAdmUsuario = new Models.AdmUsuario();
oAdmUsuario.Au_codusuario = login.UserName;
Servicio.RetornaEntidad<Models.AdmUsuario>(ref Mensaje, "admsis.adm_usuario", oAdmUsuario.getPk(), oAdmUsuario);
***Models.AdmUsuario.UserWeb = oAdmUsuario;***
FormsAuthentication.SetAuthCookie(login.UserName, false);
Session["Modulo"] = null;
Session["Menu"] = null;
return RedirectToAction("index", "raMainReclamo", new { area = "Reclamos" });
}
In the model I define:
public static AdmUsuario UserWeb;
But I can't access to value.
Do you have any idea, how I can to access the values of an object from different controllers in different areas?
You need a way to store the object between requests. You could put the object in Session Memory and pull it back out.
{
// Other Code
Session["AdmUsuario"] = oAdmUsuario;
return RedirectToAction("index", "raMainReclamo", new { area = "Reclamos" });
}
Controller in Reclamos Area
public class raMainReclamoController : Controller
{
public ActionResult Index() {
var oAdmUsuario = Session["AdmUsuario"] as Models.AdmUsuario;
// Other Code
}
}
However, the a more standard approach would be to persist the object to a database and then pull it back out. You could read up on using Entity Framework to access a sql database. I like to use RavenDB for storage as it makes saving objects really easy.
** UPDATE IN RESPONSE TO COMMENTS **
This is just psuedo code as I don't know what you are using to connect to postgres.
{
// Other Code
oAdmUsuario = postgresContext.Store(oAdmUsuario);
postgresContext.SaveChanges();
return RedirectToAction("index", "raMainReclamo", new { area = "Reclamos", id = oAdmnUsuario.Id });
}
Controller in Reclamos Area
public class raMainReclamoController : Controller
{
public ActionResult Index(int id) {
var oAdmUsuario = postgresContext.GetById<Models.AdmUsuario>(id);
// Other Code
}
I have two controller actions outlined below:
public ViewResult TitleStorylines(int id)
{
var vm = Service.Get(id);
vm.IsEditable = User.HasPermission(SecurityPermissionType.ManageStorylines);
return View(vm);
}
public ViewResult TitleStorylinesCreate(TitleStorylineModel model)
{
var created = Service.Create(model);
return TitleStorylines(created.TitleId);
}
I only have one view in my project, called TitleStorylines, which the first controller action handles fine. But when I call the second method, it gives me an error saying that it can't find the view called TitleStorylinesCreate even though I'm explicitly calling the previous method. What gives?
Did you try ?
return View("TitleStorylines",created.TitleId);
EDIT: Based on your update : I guess you are posting your form back the TitleStorylinesCreate. So probably after saving, dont you want to redirect the user back to the Get action of same ?
[HttpPost]
public ViewResult TitleStorylinesCreate(TitleStorylineModel model)
{
var created = Service.Create(model);
return RedirectToAction("TitleStorylines",new { #id=created.TitleId});
}
In the above example we are doing the PRG pattern. Post -> Redirect -> Get
After saving, we are redirecting them back to the first method. It will be a HTTP GET method.
public ActionResult TitleStorylinesCreate(TitleStorylineModel model)
{
var created = Service.Create(model);
return RedirectToAction("TitleStorylines",new { #id=created.TitleId});
}
I have 2 actions on a controller:
public class CalculatorsController : Controller
{
//
// GET: /Calculators/
public ActionResult Index()
{
return RedirectToAction("Accounting");
}
public ActionResult Accounting()
{
var combatants = Models.Persistence.InMemoryCombatantPersistence.GetCombatants();
Debug.Assert(combatants != null);
var bvm = new BalanceViewModel(combatants);
Debug.Assert(bvm!=null);
Debug.Assert(bvm.Combatants != null);
return View(bvm);
}
}
When the Index method is called, I get a null model coming out. When the Accounting method is called directly via it's url, I get a hydrated model.
This is less an answer than a workaround. I am not sure why you are getting a null model as it looks like it should work. In fact, I can confirm the behavior you are seeing when I try it out myself. [EDIT: I discovered a flaw in my initial test code that was causing my own null model. Now that that is corrected, my test works fine using RedirectToAction.] If there is a reason for it, I don't know it off the top of my head.
Now for the workaround...I assume that you are doing it this way since the default route sends all traffic to http://www.domain.com/Calculators to "Index". So why not create a new route like this:
routes.MapRoute(
"Accounting",
"Calculators/{action}/",
new { controller = "Calculators", action = "Accounting" }
);
This route specifies the default action to the Calculators controller will be "Accounting" instead of Index.
Your view for the Action Accounting expects a model. (the BalanceViewModel). The index action method does not have a instance of the BalanceViewModel.
There are a number of ways you can solve this. In your View (aspx page) you can check for nulls...
Or in the index action method, you create a new instance of a BalanceViewModel and store it in TempData, and then retrieve this in your view when your model is null.
Or in your action method, you could also call return View("Accounting", new BalanceViewModel()) instead of using redirect to action.
EDIT: Example Code -
If you want to share this functinality, create a private method like this:
public class CalculatorsController : Controller {
// GET: /Calculators/
public ActionResult Index() {
return View(GetBalanceViewModel());
}
public ActionResult Accounting() {
return View(GetBalanceViewModel());
}
private BalanceViewModel GetBalanceViewModel() {
var combatants = Models.Persistence.InMemoryCombatantPersistence.GetCombatants();
Debug.Assert(combatants != null);
var bvm = new BalanceViewModel(combatants);
Debug.Assert(bvm != null);
Debug.Assert(bvm.Combatants != null);
return bvm;
}
}
Have you seen this Question?