How to throw an exception when member comes twice on Deserializing with JsonConvert

Question

I have JSON which contains duplicated members:

[
  {
    "MyProperty": "MyProperty1",
    "MyProperty": "MyWrongProperty1",
    "MyProperty2": "MyProperty12",
    "MyProperty2": "MyWrongProperty2"
  },
  {
    "MyProperty": "MyProperty21",
    "MyProperty2": "MyProperty22"
  }
]

When I deserialize, it is getting the last property. Here is the code:

var myJson = File.ReadAllText("1.txt");
List<MyClass> myClasses = JsonConvert.DeserializeObject<List<MyClass>>(myJson);

But I need to throw an exception when JSON string contains duplicated properties. How can I do that?

Use a custom Converter using the `JsonConverter`. Refer https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to — Sathish Guru V, May 16 '20 at 08:22
This might help: https://stackoverflow.com/questions/20714160/how-to-deserialize-json-with-duplicate-property-names-in-the-same-object — Willy David Jr, May 16 '20 at 08:32
Does this answer your question? [How to deserialize JSON with duplicate property names in the same object](https://stackoverflow.com/questions/20714160/how-to-deserialize-json-with-duplicate-property-names-in-the-same-object) — Pavel Anikhouski, May 16 '20 at 08:47
@maytham-ɯɐɥʇʎɐɯ Actully, it seems to be an exact duplicate, as well as many others questions on this site, which can be found by googling within few minutes (like [Json.NET (Newtonsoft.Json) - Two 'properties' with same name?](https://stackoverflow.com/questions/3877526/json-net-newtonsoft-json-two-properties-with-same-name). One of the answers below shows the same approach with answers in duplicates — Pavel Anikhouski, May 16 '20 at 10:07

score 2 · Answer 1 · answered May 16 '20 at 08:33

You can use JsonTextReader from Newtonsoft.Json to get all tokens which are of PropertyName and then probably use LINQ GroupBy() like

string json = "[
  {
    "MyProperty": "MyProperty1",
    "MyProperty": "MyWrongProperty1",
    "MyProperty2": "MyProperty12",
    "MyProperty2": "MyWrongProperty2"
  },
  {
    "MyProperty": "MyProperty21",
    "MyProperty2": "MyProperty22"
  }
]";

List<string> props = new List<string>();

JsonTextReader reader = new JsonTextReader(new StringReader(json));
while (reader.Read())
{
    if (reader.Value != null && reader.TokenType == "PropertyName")
    {
        props.Add(reader.Value);
    }
}

Now use GroupBy() on the list to see duplicates

var data = props.GroupBy(x => x).Select(x => new 
           {
             PropName = x.Key,
             Occurence = x.Count()
           }).Where(y => y.Occurence > 1).ToList();

If (data.Any())
{
  Throw New Exception("Duplicate Property Found");
}

score 2 · Accepted Answer · answered May 16 '20 at 08:41

2

You need to added DuplicatePropertyNameHandling = DuplicatePropertyNameHandling.Error in your JsonLoadSettings.

You can dig in details following this answer.

There is also a thread from Newtonsoft.json that cover this topic.

answered May 16 '20 at 08:41

Maytham Fahmi

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How to throw an exception when member comes twice on Deserializing with JsonConvert

2 Answers2