Newtonsoft.json: Handling duplicate elements in JSON payload

[dmoeff]

What is the best way with Json.NET to restrict occurrence of duplicate elements in JSON payload?
For example:
{
"role" : "default",
"username" : "mallory",
"role": "admin",
"password" : "Evil123!"
}

[thebothead]

I would like to know how to do this using the JSON.NET schema library as well.

[thebothead]

According to the spec as well:

2.2. Objects

An object structure is represented as a pair of curly brackets
surrounding zero or more name/value pairs (or members). A name is a
string. A single colon comes after each name, separating the name
from the value. A single comma separates a value from a following
name. The names within an object SHOULD be unique.

  object = begin-object [ member *( value-separator member ) ]
  end-object

  member = string name-separator value

[JamesNK]

You will need to use JsonTextReader

[thebothead]

We tried that. The text reader does not restrict duplicates, in fact it
seems to allow them and uses the last property/value combination specified.
On Jun 6, 2016 5:28 PM, "James Newton-King" [email protected]
wrote:

You will need to use JsonTextReader

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[JamesNK]

Oh I misunderstood. There is no way in Json.NET to restrict them. It will use the last value.

[thebothead]

Seeing as the JSON spec indicates valid JSON should contain unique names
within an object it seems like this should be a feature of the
validation/schema library of JSON.NET? Perhaps a feature request is in
order?
On Jun 6, 2016 6:09 PM, "James Newton-King" [email protected]
wrote:

Oh I misunderstood. There is no way in Json.NET to restrict them. It will
use the last value.

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[dmoeff]

        {
            var message =   "{" +
                                "\"DeviceAdded\" :" + 
                                "{" +
                                    "\"DeviceId\" : \"SN123456\"," +
                                    "\"Protocols\" : []," +
                                    "\"DeviceType\" : \"UPS\"," +
                                    "\"Model\" : \"12345\"," +
                                    "\"HardwareVersion\" : \"1.0.0.0\"," +
                                    "\"FirmwareVersion\" : \"2.0.0.0\"," +
                                    "\"SoftwareVersion\" : \"3.0.0.0\"," +
                                    "\"SerialNumber\" : \"1\"," +
                                    "\"SerialNumber\" : \"456\"" +
                                "}" +
                            "}";

            var jobj = JsonConvert.DeserializeObject<JObject>(message);
            Console.WriteLine(jobj);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.GetType());
            Console.WriteLine(ex.Message);
        }

If I use Newtonsoft.Json 6.0.8 I get exception System.ArgumentException: Can not add property SerialNumber to Newtonsoft.Json.Linq.JObject. Property with the same name already exists on object.

If I use Newtonsoft.Json 8.0.2 the code executes without error. What changed between these two versions? How with Newtonsoft.Json 6.0.8 I can get the same behavior as with Newtonsoft.Json 6.0.8?

[IanYates]

What changed between these two versions? How with Newtonsoft.Json 6.0.8 I can get the same behavior as with Newtonsoft.Json 6.0.8?

A lot I suspect. You've accidentally specified the same version twice in your sentence. Are you trying to get 8.0.2 to behave like 6.0.8, or make 6.0.8 behave like 8.0.2?

[dmoeff]

I would like 8.0.2 to behave as 6.0.8 in that when duplicate elements occurs in JSON payload an exception to be thrown. For example:

var message = "{" +
"\"role\" : \"default\"," +
"\"username\" : \"mallory\"," +
"\"role\" : \"admin\"," +
"\"password\" : \"password!\"" +
"}";
var jobj = JsonConvert.DeserializeObject(message);

Here "role" element occurs twice. In this case 6.0.8 will throw a System.ArgumentException exception, where 8.0.2 deserialize it successfully with admin value for the "role".

[dbjorge]

@JamesNK My team would really like to be able to detect this case. Would you be amenable to a PR that adds a new JsonSerializerSettings option for switching between the current "accept last" behavior and "emit parse error" behavior?

[JamesNK]

JsonLoadSettings will have a DuplicatePropertyNameHandling options. Setting it to DuplicatePropertyNameHandling.Error will throw when a duplicate property name is encountered.

[davidagross]

How can this functionality be employed by patterns that use JsonConvert.DeserializeObject? If it can't, I'd like to open an issue to add this functionality to JsonSerializerSettings.

[imtrobin]

I just found this issue too. I thought it was supposed to throw, and it didn't.

[mikhail-barg]

How can this functionality be employed by patterns that use JsonConvert.DeserializeObject? If it can't, I'd like to open an issue to add this functionality to JsonSerializerSettings.

see #1922:
с# new JsonLoadSettings { DuplicatePropertyNamesHandling = DuplicatePropertyNamesHandling.Throw }

[mschmitz2]

How can this functionality be employed by patterns that use JsonConvert.DeserializeObject? If it can't, I'd like to open an issue to add this functionality to JsonSerializerSettings.

see #1922:

new JsonLoadSettings { DuplicatePropertyNamesHandling = DuplicatePropertyNamesHandling.Throw }

@mikhail-barg could you elaborate on how one can pass the JsonLoadSettings into JsonConvert.DeserializeObject, which, as I understand, only takes a string and JsonSerializerSettings as arguments?

public static T DeserializeObject<T>(string value, JsonSerializerSettings settings)

Thanks!

[DanCarterGMSL]

+1 for adding this as a property to JsonSerializerSettings.

I'm using Json.NET indirectly through ASP.NET Core, and I was surprised to see it behaving this way.

[rajrao]

While we wait for JsonSerializerSettings to get this behavior, I have found this code to work:

public object DeserializeObject(string json, JsonSerializerSettings settings)
{
    JsonSerializer jsonSerializer = JsonSerializer.CreateDefault(settings);
    using (var stringReader = new StringReader(json))
    using (var jsonTextReader = new JsonTextReader(stringReader))
    {
                jsonTextReader.DateParseHandling = DateParseHandling.None;
        JsonLoadSettings loadSettings = new JsonLoadSettings { 
                                                DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error 
                                            };
        var jtoken = JToken.ReadFrom(jsonTextReader, loadSettings);
        return jtoken.ToObject<object>(jsonSerializer);
    }
}