Asp.Net Web API Error: The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'

Question

Simplest example of this, I get a collection and try to output it via Web API:

// GET api/items
public IEnumerable<Item> Get()
{
    return MyContext.Items.ToList();
}

And I get the error:

Object of type
'System.Data.Objects.ObjectQuery`1[Dcip.Ams.BO.EquipmentWarranty]' cannot be converted to type
'System.Data.Entity.DbSet`1[Dcip.Ams.BO.EquipmentWarranty]'

This is a pretty common error to do with the new proxies, and I know that I can fix it by setting:

MyContext.Configuration.ProxyCreationEnabled = false;

But that defeats the purpose of a lot of what I am trying to do. Is there a better way?

Azores

How does turning off the proxy defeat serializing an object? – Oidium

Its a proxy object, not the actual POCO – Azores

Turning off the proxy globally means that you don't get to use lazy-loaded navigation properties. I agree that that's not a proper solution if you need the navigation properties. Still looking for an answer myself for this problem. – Rosenkranz

Answer 1

I would suggest Disable Proxy Creation only in the place where you don't need or is causing you trouble. You don't have to disable it globally you can just disable the current DB context via code...

    [HttpGet]
    [WithDbContextApi]
    public HttpResponseMessage Get(int take = 10, int skip = 0)
    {
        CurrentDbContext.Configuration.ProxyCreationEnabled = false;

        var lista = CurrentDbContext.PaymentTypes
            .OrderByDescending(x => x.Id)
            .Skip(skip)
            .Take(take)
            .ToList();

        var count = CurrentDbContext.PaymentTypes.Count();

        return Request.CreateResponse(HttpStatusCode.OK, new { PaymentTypes = lista, TotalCount = count });
    }

Here I only disabled the ProxyCreation in this method, because for every request there is a new DBContext created and therefore I only disabled the ProxyCreation for this case . Hope it helps

Rincon

Answer 2

if you have navigation properties and you do not want make them non virtual, you should using JSON.NET and change configuration in App_Start to using JSON not XML!
after install JSON.NET From NuGet, insert this code in WebApiConfig.cs in Register method

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);

Ickes

Adding the code in the config works. Suppose JSON.NET is added by default with the new webapi project on VS15 – Ratio

Answer 3

If you have navigation properties make them non virtual. Mapping will still work but it prevents the creation of Dynamic Proxy entities which cannot be serialized.]

Not having lazy loading is fine in a WebApi as you don't have a persistent connection and you ran a .ToList() anyway.

Bromeosin

I had the same issue and making the navigation properties non virtual does the trick but I am curious to know if there are any drawbacks to this technique? Thanks! – Whitt

@Whitt marking them as vitual will allow the class to be overridden internally. EF will override to allow for lazy loading, for example, it will only fetch internal lists or properties when they are requested. In the case of MVC or something where there is disconnected architecture it really makes no difference as you need all the data immediately. – Bromeosin

Answer 4

I just disabled proxy classes on a per needed basis:

    // GET: ALL Employee
    public IEnumerable<DimEmployee> Get()
    {
        using (AdventureWorks_MBDEV_DW2008Entities entities = new AdventureWorks_MBDEV_DW2008Entities())
        {
            entities.Configuration.ProxyCreationEnabled = false;
            return entities.DimEmployees.ToList();
        }
    }

Fanti

Answer 5

Add the following code in Application_Start function of Global.asax.cs:

GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings
    .ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
GlobalConfiguration.Configuration.Formatters
    .Remove(GlobalConfiguration.Configuration.Formatters.XmlFormatter);

This instruct the API to serialize every response into JSON and remove XML responses.

Davon

Answer 6

In my case the object being returned had a property within it with a type that did not have an argumentless/default constructor. By adding a zero-argument constructor to that type the object could be serialized successfully.

Antidote

Answer 7

I had the same problem and my DTO was missing an parameter less constructor.

public UserVM() { }

public UserVM(User U)
    {
        LoginId = U.LoginId;
        GroupName = U.GroupName;
    }

First constructor was missing.

Bermuda

Answer 8

I got this error message and it turns out the problem was that I had accidentally set my class to use the same serialized property name for two properties:

public class ResultDto
{
    //...
    [JsonProperty(PropertyName="DataCheckedBy")]
    public string ActualAssociations { get; set; }
    [JsonProperty(PropertyName="DataCheckedBy")]
    public string ExpectedAssociations { get; set; }
    //...
}

If you're getting this error and you aren't sending entities directly through your API, copy the class that's failing to serialize to LINQPad and just call JsonConvert.SerializeObject() on it and it should give you a better error message than this crap. As soon as I tried this it gave me the following error message: A member with the name 'DataCheckedBy' already exists on 'UserQuery+ResultDto'. Use the JsonPropertyAttribute to specify another name.

Denbrook

Answer 9

After disable Proxy Creation, use eager loading (Include()) to load the proxy object.

Immortality

Answer 10

In my Project EntityCollection returned from the WebApi action method. Configuration.ProxyCreationEnabled = false not applicable. I have tried the below approach it is working fine for me.

1. Control Panel. 2.Turn on Windows Features on or off
2. Choose Internet Information Service
3. Check all the World Wide Web Components it would be better to check all the components in IIS.
4. Install the components.
5. Go to (IIS) type inetmgr in command prompt.
6. select the published code in the Virtual directory.
7. Convert into application
8. Browse it the application.

Pretended

Answer 11

The answer by @Mahdi perfectly fixes the issue for me, however what I noticed is that if my Newtonsoft.JSON is 11.0 version then it doesn't fix the issue, but the moment I update Newtonsoft.JSON to latest 13.0 it starts working.

Butterfat