Json.net : Do not derserialize numbers as booleans

Question

Is there any built in settings in json.net to disable the conversion of numbers to booleans. I would prefer it to return an error instead : (without writing a Custom Converter for each class that has a bool property )


    public class MyClass
    {
        public bool flag { get; set; }
    }

    var str = @"{"flag":123}";
    MyClass result = JsonConvert.DeserializeObject<MyClass>(str) ; // flag is true !

A serializer would not serialize a bool to `123`...well, not a well working one — Ňɏssa Pøngjǣrdenlarp, Feb 04 '20 at 22:31
You'll need to sanitize this data yourself first. A `bool` in this context is clearly defined by JSON.NET as non-zero being `true` and zero being `false`. Your software should not allow the entry of a number that you don't want. — Robert Harvey, Feb 04 '20 at 22:36
Only allow the user to enter `true/false`. Don't allow them to enter `123` in a boolean field — haldo, Feb 04 '20 at 22:37
You could never store `"I like pie"` or any non bool in a boolean field in a class in order to be serialized, so this appears to be an XY problem — Ňɏssa Pøngjǣrdenlarp, Feb 04 '20 at 22:39
[Json.net Schema](https://www.newtonsoft.com/jsonschema) can validate your json — Sir Rufo, Feb 04 '20 at 22:47
@ŇɏssaPøngjǣrdenlarp of course you can , if you are using a dynamic language — mLar, Feb 04 '20 at 22:51

score 1 · Accepted Answer · edited Feb 05 '20 at 04:23

You shouldn't use different types in one property to get one bool result. But if you wish not to declare one custom JsonConvert for every property in the class, you can always create DefaultSettings in your code.

void Initialize()
{
    JsonConvert.DefaultSettings = () => new JsonSerializerSettings
    {
        Converters = new List<JsonConverter>
        {
            new BoolJsonConverter()
        }
    };
}

// Create JsonConvert you want to add to DefaultSettings
public class BoolJsonConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(bool);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {

    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {

    }
}

var json = @"{""flag"":123}"
var myClass = JsonConvert.DeserializeObject<MyClass>(json);

Complete code is available in https://stackoverflow.com/a/9741557/477420 — Alexei Levenkov, Feb 04 '20 at 23:27

score 0 · Answer 2 · answered Feb 04 '20 at 22:42

I'm assuming this is a Deserialize only situation. If that is the case, you could have your int value go into an int and use another var to hold the bool. Something like -

public class MyClass
{
    public int flagInt { get; set; }

    [JsonIgnore]
    public bool flag
    {
        get
        {
            switch (flagInt)
            {
                case 0: return false;
                case 1: return true;
                default: throw new Exception("Cannot convert flag to bool");
            }
        }
    }
}

Note that I don't have a setter on flag so doing something like flag = false will not have expected results and will not serialize correctly either.

good trick, but it needs to be implemented on every boolean property of every class of the application — mLar, Feb 04 '20 at 22:54

Json.net : Do not derserialize numbers as booleans

2 Answers2