返回JSON时的C＃递归限制

Question

I ran into an annoying issue recently. I'm going to simplify my datamodel here, but the principle is just the same. I have a class "User". In that class I have a property that is a list of objects the user owns. I also have this class "object". Because every "object" has an owner, it has a property of type "User", which links to its owner. Now, what I'm trying to do is basically this

return Json(myUser,JsonRequestBehavior.AllowGet);

When I load the page, it takes like 30 seconds and then I get the error "RecursionLimit exceeded".

I guess this is because the objects are linking to each other. Now my question is, how can I tell "Json" that it shouldn't go deeper then 1 level of objects to avoid this?

Answer 1

myUser is probably a type generated by EntityFramework.

When you return Json, the framework is going to prepare each property in essence firing off SQL command to lazy-load all the data.

Instead, you should prepare a ViewModel class with concrete properties not attached to EntityFramework and prepare that object as deep as you want it to go.

Answer 2

It might happen when your object has some properties of itself. for example.

public object Employee()
{
    string ID {get; set;}
    string Name {get; set;}
    int Age {get; set;}
    Employee Boss{get; set;} //<-- here
}

var employee = new Employee();
return Json(employee,JsonRequestBehavior.AllowGet); //The Boss property will cause "RecursionLimit exceeded".

To avoid that. you can do something like that:

var employee = new Employee();
var prepareForJson = new {
    ID = employee.ID,
    Name = employee.Name,
    Age = employee.Age,
    Boss = employee.Boss.ID
};
return Json(prepareForJson , JsonRequestBehavior.AllowGet);

Answer 3

You can configure recursion depth through web.config

http://msdn.microsoft.com/en-us/library/bb763183.aspx

but you probably just want to sort out your model not to have recursion in the first place. Think how much data is needed in your current situation and return just that.

Answer 4

I think Edison Chuang is the answer for the vast majority of cases (mapping data models to some service models that do not have those navigation properties that will most certainly cause loops during the serialization).

However, since most of the service models will share many of the properties of the data models (EF models), AutoMapper can be used, greatly simplifying code especially for objects with many properties. Eg:

// set up map
cfg.CreateMap<Employee, EmployeeSm>();

// use the map
var sm = Mapper.Map<EmployeeSm>(employee);
// this can be also set up during mapping configuration phase
sm.Boss = employee.Boss.ID;

For those rare cases when serialization depth goes beyond the default 100, you can either increase this limit or use Json.NET to serialize your objects.