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Why asp.net core sending empty object as response?

When I debug the code in VS, the cities list, which I am returning have 3 objects in it along with the properties. When I call this endpoint I am receiving a response of 3 list items of empty objects.
How to resolve this issue?
Model Class:
public class City
{
public string CityName;
public string AssociatedCities;
public string Province;
public int Status;
public City(string cityName, string associatedCities, string province, int status)
{
this.CityName = cityName;
this.AssociatedCities = associatedCities;
this.Province = province;
this.Status = status;
}
}
Endpoint:
[HttpGet]
[Route("cities")]
public ActionResult<IEnumerable<City>> GetCities()
{
return Ok(Cities);
}
This is how I am calling the endpoint
getCities() {
this.http.get<City[]>('/api/wizard/cities')
.subscribe(result => {
console.log(result);
this.cities = result;
}, error => console.error('Something went wrong : ' + error));
}
The response I get:
The response that is needed:
[
{
"SearchCity": "Toronto",
"AssociatedCities": "Ajax, Whitby, Toronto, Mississauga, Brampton",
"Province": "ON",
"Status": 1
},
{
"SearchCity": "Vancouver",
"AssociatedCities": "Vancouver, Vancouver City",
"Province": "BC",
"Status": 1
}
]
I have tried this already: Fresh ASP.NET Core API returns empty JSON objects

System.Text.Json currently does not support serialization/deserialization of fields and non-parameter-less, non-default constructors.
Your example model uses both fields and a non-default constructor. If you need to use a custom constructor for some reason, you would need to implement your own JsonConverter<T> to support that. This doc might be helpful for that:
https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-migrate-from-newtonsoft-how-to#deserialize-to-immutable-classes-and-structs
Only public properties with public getters/setters are supported along with the default, parameter-less constructor (what is referred to as Plain_old_CLR_object (POCO)). Note: If you are only serializing (i.e. writing), the setters generally don't have to be public.
Properties are different from fields (and contain getters/setters).
Here is the fix:
public class City
{
public string CityName { get; set; }
public string AssociatedCities { get; set; }
public string Province { get; set; }
public int Status { get; set; }
}

In my case, I just added this in my ConfigureServices method in Startup.cs (I am using Dot Net 5.0)
services.AddControllers().AddNewtonsoftJson();

Based on the fact that all your action does is return Cities, which presumably is a property or field defined on your controller, I'm going to take a shot in the dark and assume that you're setting that in another request and expecting it to still be there in this request. That's not how it works. The controller is instantiated and disposed with each request, so anything set to it during the lifetime of a request will not survive. As a result, Cities has nothing in this request, so you get an empty response.
If you need a list of cities in the action, then you should query those in that action. Also, for what it's worth, System.Text.Json does not currently support serializing fields, as others have mentioned in the comments, but you may still use JSON.NET instead, which does. See: https://learn.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.1&tabs=visual-studio#jsonnet-support

Building json response

I'm working on a self hosting rest api used to monitor de status of several servers.
I was tasked that, when everything is working correctly, I should only return
{"response":"ok"}
But, when there's an error on queried server, or servers, I must return
{ "response" : [ {"agent":"<server>:<port>","port":"<port>" ,"Error":"<Description of the error>"} ] }
I was thinking on building a helper class to build object on this schema and returning them over the rest api
public class HelperErrorResponseClass
{
public string agent { get; set; }
public string port { get; set; }
public string Error { get; set; }
}
This is no problem, the issue is, how to deal when everything it ok. I have this Api response helper class
public class Response
{
public string response { get; set; }
}
But I'm seeing that I'll need to change the response property to List<HelperErrorResponseClass> in order to send the error response. Do you think that, if I stringify the List<HelperErrorResponseClass> object with Json.Net it will be returned in the desired format?
Edit: Forgot to add that, I-m using Web Api to build the rest service.
UDPATE:
After further research, I found a way to work this out.
Following this post, I was able to rewrite the helper classes like this
[DataContract]
[KnownType(typeof(List<HelperErrorResponseClass>))]
public class Response
{
[DataMember]
public object response { get; set; }
}
[DataContract]
public class HelperErrorResponseClass
{
[DataMember(EmitDefaultValue = false)]
public string agent { get; set; }
[DataMember(EmitDefaultValue = false)]
public string port { get; set; }
[DataMember(EmitDefaultValue = false)]
public string error { get; set; }
}
This work to fulfill my and my client needs... except for one little thing. When I get the result from a List, and given that I added the KnownTypes directive, my response is now this
{"response":[{"__type":"HelperErrorResponseClass:#AppCommonLib","Error":"ERROR","InstanceId":"<InstanceId> : <Port>","PortType":"<PortType>"},{"__type":"HelperErrorResponseClass:#AppCommonLib","Error":"ERROR","InstanceId":"<InstanceId> : <Port>","PortType":"<PortType>"}]}
Any idea how to get rid of that __type property of the response? make that it must be explicit to only return the declared properties of the helper class?

Simplest way to deal with this is to set the return type on the handling function to string, then you can check for errors and do something like;
//pseudo code to give an idea
if (errorsList.Count() > 0)
{
return JsonConvert.SerializeObject(errorsList);
}
else
{
return JsonConvert.SerializeObject(new Response("ok"));
}
Now this being said... Unless the people providing requirements aren't at all flexible you should just redo the design. How about just returning the errors array and the person calling the API can infer that if it's length is 0 then everything is working OK. Seems pretty straight forward, right? You could also just put all the properties on one object and those fields would just come back as null or empty strings. Or you could change you serializer settings to exclude them if they don't have a value.

Keep things simple and use an anonymous type.
if (condition)
{
return JsonConvert.SerializeObject(new { response = new { agent = "x", port = "y", error = "z" }});
}
else
{
return JsonConvert.SerializeObject(new { response = "ok"});
}
More info:
https://msdn.microsoft.com/en-us/library/bb397696.aspx

I personally don't think you need a Response class, especially that it is of object type. IMHO, you've overcomplicated the very simple issue that you have. It is not only the __type, but also other info like HelperErrorResponseClass:#AppCommonLib that isn't supposed to be there.
Another Issue you have is the incorrect name of the HelperErrorResponseClass class. This is not a helper class. It is a standard data-object class.
A helper class is a class filled with static methods. It is usually used to isolate a "useful" algorithm.
This is how I would do it:
I'd get rid of the Response class.
I'd use your original simple HelperErrorResponseClass class, but rename it to something more meaningful like ErrorDetails.
I'd return the response like this:
.
if (errorsList.Count() > 0) {
return JsonConvert.SerializeObject(new { response = errorsList});
}
else {
return JsonConvert.SerializeObject(new { response = "ok"});
}
However, if you really want to stick to your updated solution, an easy way to get rid of the __type is simply removing it from the final serialized string:
if (errorsList.Count() > 0) {
string r = JsonConvert.SerializeObject(new { response = errorsList});
return r.Replace("__type", "");
}
else {
return JsonConvert.SerializeObject(new { response = "ok"});
}

mapping ajax data in c# using object binder

The following screen shot shows the data I'm sending (shown with firebug in firefox).
The code below then shows the method the ajax method calls. The Date and Id properties are correctly populated when hitting the server side method call but my array (of type CustomerRequests) has no values inside it, however the number of CustomerRequests in the post is correct.
Any ideas?
Thanks
My Controller method
public ActionResult Show(Customers request)
{
..
// Number of request.CustomerRequests is correct
// Although request.CustomerRequests[0].Name == null ?? which is wrong
Customers class below:
[DataContract]
public class Customers
{
[DataMember]
public CustomerRequests[] CustomerRequests{ get; set; }
[DataMember]
public DateTime Date { get; set; } // I can see this value
[DataMember]
public int Id{ get; set; } // I can see this value
}
[DataContract]
public class CustomerRequests
{
[DataMember]
public string Name { get; set; }
[DataMember]
public string Expression { get; set; }
}
Javascript
$('textarea').each(function () {
var theName = 'The Name';
var theExpression = 'The Expression';
var obj = {
'Name': theName,
'Expression': theExpression
};
expressionArray.push(obj);
}); // close each
// val is the posted data
var val = {
'Id': '1',
'Date': '2013-10-10',
'CustomerRequests': $.makeArray(expressionArray)
};
I've tried although it doesn't work.
JSON.stringify({ Customers: val })

After all, we just have to add a content-type to your call and to remove the name from data.
It's something like
$.ajax({
url: '/controller/action',
cache: false,
type: 'POST',
contentType: 'application/json; charset=utf-8',
data: JSON.stringify(viewModel)
});
Please note that:
hard coding the URL is a bad practice. You should use #Url.Content("") or something like that
JSON.stringify may not work with older browsers. You may need to add this lib: http://www.json.org/js.html

Although this is not exactly an answer, because I have never used the built-in serializers, I can advise you to use the Json.NET library. I've been using it now for a long time, and I like it very much.
As for your question, I would try using List<T> instead of array, and I would probably try to instantiate the List in the constructor of the model. But these are just guesses, to be honest.

Issue with Entity Framework class being returned via Web Service

I've implemented a web service and I am calling it via ajax.
Note: My entities have been made for an entity framework code first purpose.
My ajax looks as follows:
$.ajax({
type: "GET",
url: "/MyProject/MyService.svc/GetEntity",
data: "entityID=1",
dataType: "json",
contentType: "application/json; charset=utf-8",
success: AjaxSucceeded,
error: function (msg, status, extra) {
alert(status + " - " + extra);
}
});
AjaxSucceeded is simply a function with the data variable where I am simply logging the data in the console.
My GetEntity function currently looks like this:
[OperationContract]
[WebGet(ResponseFormat = WebMessageFormat.Json)]
public MyEntity GetEntity(int entityID)
{
AccessObject accessObject = new AccessObject("MyConnectionString");
MyEntity theEntity = accessObject.GetByID(entityID);
return theEntity;
}
I have tested this with a class created purposefully for testing and it worked as expected (for example, I created a MyEntity class within the web service that was very simple, a couple of properties and no other methods etc.).
The problems arises when I return an entity that I have made for code first Entity Framework. It doesn't work, the web service function is called multiple times and then an error appears in the console stating "Failed to load resource" referring to my service function.
For reference, here is my entity:
[DataContract(IsReference=true)]
public class MyEntity
{
#region Properties
[Key]
[DataMember]
public int ID { get; set; }
public bool SomeBoolean { get; set; }
[StringLength(1000)]
public string Description { get; set;}
#endregion
#region Relationships
public virtual SomeOtherEntity OtherEntity { get; set; }
#endregion
}
I have only set the ID to be DataMember for testing but still no success.
Could anyone point me in the correct direction? I know the web service works because other functions work and if I set up a local (within the web service) class it will return that with no issues. So I'm of the assumption that it has something to do with the entity framework attributes? I may be wrong but that's all I can imagine.
Thank you for your time.
Oh also, for reference, my service class has the following attributes:
[ServiceContract(Namespace = "")]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]

The problem is simply Entities aren't really built for serialization. My advice would be to create a DTO, map the relevant properties across and pass that over the wire instead e.g.
public class EntityDto
{
public int ID { get; set; }
public string Description { get; set; }
...
}
[OperationContract]
[WebGet(ResponseFormat = WebMessageFormat.Json)]
public EntityDto MyEntity(int entityId)
{
AccessObject accessObject = new AccessObject("MyConnectionString");
MyEntity theEntity = accessObject.GetByID(entityID);
return new EntityDto()
{
ID = theEntity.ID,
Description = theEntity.Description,
...
};
}

Trouble model binding a JSON array to a List in ASP.NET MVC 3

I am having trouble model binding a JSON array to a C# list in MVC 3.
I have an object called a DockState. It looks like this:
[Serializable]
public class DockState
{
public bool Closed { get; set; }
public bool Collapsed { get; set; }
public string DockZoneID { get; set; }
public int ExpandedHeight { get; set; }
public Unit Height { get; set; }
public int Index { get; set; }
public Unit Left { get; set; }
public bool Pinned { get; set; }
public bool Resizable { get; set; }
public string Tag { get; set; }
public string Text { get; set; }
public string Title { get; set; }
public Unit Top { get; set; }
public string UniqueName { get; set; }
public Unit Width { get; set; }
}
My action method accepts a list of dock states, like this:
public JsonResult SaveDockStates(List<DockState> dockStates)
On the client I am building an array of JSON objects that contain all the same properties as the C# DockState object. I am then assigning this array to a JSON object of its own with the property of the argument in the action method, like this:
function get_allDockStates()
{
var allRadDocks = []; // declare array.
var allRadControls = $telerik.radControls; // use telerik API to obtain all controls.
// loop through all telerik controls.
for (var i = 0; i < allRadControls.length; i++)
{
var element = allRadControls[i];
// Check if control is a rad dock element.
if (Telerik.Web.UI.RadDock && element instanceof Telerik.Web.UI.RadDock)
{
// Build a JSON object containing the same properties as the C# DockState
// object. Leaving out a couple that should just be null anyway. Add new
// JSON object to array.
Array.add(allRadDocks,
{
UniqueName: element._uniqueName,
DockZoneID: element._dockZoneID,
Width: element._width,
Height: element._height,
ExpandedHeight: element._expandedHeight,
Top: element._top,
Left: element._left,
Resizable: element._resizable,
Closed: element._closed,
Collapsed: element._collapsed,
Pinned: element._pinned,
Title: element._title,
Index: element._index
});
}
}
// Return the array.
return allRadDocks;
}
// This function is fired by the rad dock controls when they are moved.
function positionChanged(sender, e)
{
// obtain the array of dock states.
var dockStates = get_allDockStates();
// Make ajax call to MVC action method to save dock states.
jQuery.ajax({
data: { dockStates: dockStates },
type: 'POST',
dataType: 'json',
url: '/AjaxServices/DashboardService/SaveDockStates'
});
}
Unfortunately something rather odd happens when the AJAX call is made. It hits the action method and my List<DockState> does have items in it.
http://www.codetunnel.com/content/images/dockStateListInstantiated.jpg
However, the items in the list are all default. Meaning all their values are the default values, not the ones submitted in the request.
http://www.codetunnel.com/content/images/dockStatesDefaultValues.jpg
I'm not sure why the list contains the correct number of items, but all items appear to be nothing more than instantiated. Their properties were not set to the values in the JSON array. The request definitely contains the right data, as shown here:
http://www.codetunnel.com/content/images/dockStatesFormData.jpg
Am I doing something wrong? Is the form data formatted incorrectly? Is there a problem with the default model binder?
Update (testing Darin Dimitrov's answer)
I discovered that JSON was being overridden by an unused old script. I have removed and now JSON.stringify is working fine. Here is the request payload.
http://www.codetunnel.com/content/images/dockStatesJsonStringify.jpg
Much better. However now when I am debugging my list has zero items in it. This did not seem to fix the problem, though I appreciate the effort :)

Try sending a JSON request:
jQuery.ajax({
// TODO: Never hardcode urls like this => always use URL helpers
// when you want to generate an url in an ASP.NET MVC application
url: '/AjaxServices/DashboardService/SaveDockStates',
type: 'POST',
data: JSON.stringify({ dockStates: dockStates }),
contentType: 'application/json; charset=utf-8',
success: function(result) {
// TODO: process the results
}
});
The JSON.stringify method is natively built into modern browsers. If you want to support legacy browsers you need to include the json2.js script to your page.