Convert decimals to integer when deserializing JSON using Newtonsoft.Json

Question

Is it possible to convert decimals to integer when deserializing JSON using Newtonsoft.Json?

Suddenly our service is receiving JSON data containing decimal values where int types are expected, example: 18483.0.

As a result exceptions are thrown like "Newtonsoft.Json.JsonReaderException: Input string '18483.0' is not a valid integer."

Obviously this specific property is defined as integer, and I prefer not to change it to some decimal type, but to convert the input to int, and stripping the decimals (which are always .0 anyway).

Does this answer your question? [Custom deserializer only for some fields with json.NET](https://stackoverflow.com/questions/41510242/custom-deserializer-only-for-some-fields-with-json-net) — Crowcoder, Sep 20 '22 at 14:14

Eldar · Accepted Answer · 2022-09-20T15:10:02.937

4

You can have a custom generic JsonConverter like below :

public class CustomIntConverter : JsonConverter<int>
{
    public override void WriteJson(JsonWriter writer, int value, JsonSerializer serializer)
    {
        writer.WriteValue(value.ToString());
    }

    public override int ReadJson(JsonReader reader, Type objectType, int existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        return Convert.ToInt32(reader.Value);
    }
}

It tries to cast it to an integer if it fails then it casts it to a double and then to an int. You can use it like below :

var json = @"{""B"":42.0}";
var result = JsonConvert.DeserializeObject<A>(json, new CustomIntConverter());

Fiddle

Edit Applied @vernou's suggestion

edited Sep 20 '22 at 15:10

answered Sep 20 '22 at 14:22

Eldar

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1

Using a safe cast `return reader.Value as int ?? ((int)(double)reader.Value);` might be a simpler method than blindly casting and catching an exception – Charlieface Sep 20 '22 at 14:26
I tested, it don't work. Json.Net return integer as `long`. Then `reader.Value` is a `long` and the cast to `int` or `double` fail. You can reproduce with `var json = @"{""B"":42}";`. – vernou Sep 20 '22 at 15:01
1

It's manage more case : `return Convert.ToInt32(reader.Value);` – vernou Sep 20 '22 at 15:01
@vernou indeed Json.Net has its default as `long` – Eldar Sep 20 '22 at 15:08

Serge · Answer 2 · 2022-09-20T23:18:14.080

you can create a custom property converter

    var json = @"{ ""StringProperty"":""StringProperty"", ""IntProperty"":29.0}";

    var test = JsonConvert.DeserializeObject<Test>(json);

public class Test
{
    public string StringProperty { get; set; }

    [JsonConverter(typeof(DoubleToIntConverter))]
    public int IntProperty { get; set; }
}
    
public class DoubleToIntConverter : JsonConverter<int>
{
    public override void WriteJson(JsonWriter writer, int value, JsonSerializer serializer)
    {
        writer.WriteValue(value);
    }

        public override int ReadJson(JsonReader reader, Type objectType, int existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        return Convert.ToInt32( reader.Value);
    }
}

Convert decimals to integer when deserializing JSON using Newtonsoft.Json

2 Answers2