Is it possible to have a custom decimal precision when returning JSON data?

Question

I have a webapi returning an amount (simplified example):

so it can return for example :

{
    Amount:40
}

{
    Amount:40.1
}

{
    Amount:40.15
}

Is it possible to return always a number with 2 decimals :

{
    Amount:40.00
}

{
    Amount:40.10
}

{
    Amount:40.15
}

If you're using Json.Net, [this](https://stackoverflow.com/questions/34568963/how-can-i-force-a-minimum-number-of-decimal-places-in-json-net) may be the solution. — stuartd, Jun 27 '17 at 14:45
@SergeyBerezovskiy I agree it's the same, was just wondering if it's possible (and I dont want to return a string) — Bruno, Jun 27 '17 at 14:46
Why would you want to do this instead of handling formating with UI code? — SQLMason, Jun 27 '17 at 14:47
It changes the formatting of the number as it's converted to a string when it's written to the Json output. It's still a number. — stuartd, Jun 27 '17 at 14:51
but will it return `{ Amount:"40.10" }` or `{ Amount:40.10 }` ? In the former case, it's now a string — Bruno, Jun 27 '17 at 14:54
Number. Easy to test for yourself, but here you go: https://i.stack.imgur.com/BLz1c.png — stuartd, Jun 27 '17 at 14:59

Sergey Berezovskiy · Answer 1 · 2017-06-27T15:10:00.820

You can use custom converter which rounds each decimal value to given number of fraction digits:

public class JsonDecimalConverter : JsonConverter
{
    private int decimals;

    public JsonDecimalConverter(int decimals = 2)
    {
        this.decimals = decimals;
    }

    public override bool CanConvert(Type objectType) => objectType == typeof(decimal);

    public override object ReadJson(JsonReader reader,
       Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer,
       object value, JsonSerializer serializer)
    {
        writer.WriteValue(Decimal.Round((decimal)value, decimals));
    }
}

Usage:

var thing = new Thing { Amount = 40.12345M, Name = "Foo" };
var json = JsonConvert.SerializeObject(thing, new JsonDecimalConverter());

Output:

{
  "Amount": 40.12,
  "Name": "Foo"
}

Note that this will give you 40 for decimal number 40. Because there are no meaningful digits to be stored. 40.00 is a string formatting issue which you should handle where you want to display or store this decimal representation.

apparently @stuartd provided an example that would work even with 40: http://i.stack.imgur.com/BLz1c.png — Bruno, Jun 27 '17 at 15:14
@ibiza well, it's a little bit surprising for me that Json NET outputs value as a number. But all you gain here is a bigger size of json. After you will consume this json and deserialize it, zeroes of `40.00` will be gone. To output those zeroes you will need to format number anyway — Sergey Berezovskiy, Jun 27 '17 at 15:28

RobPethi · Answer 2 · 2017-06-27T14:55:32.877

0

You simply need to use

decimal.Round(myDecimalValue, 2)

edited Jun 27 '17 at 14:55

answered Jun 27 '17 at 14:49

RobPethi

551
9
27

1

but if I want to keep returning a number (not a string), is it possible? – Bruno Jun 27 '17 at 14:50
is your value a decimal or a double type? – RobPethi Jun 27 '17 at 14:53
the Amount is a decimal – Bruno Jun 27 '17 at 14:54
This will only work if there's actually 2 or more decimal values. 2 will return 2 and 2.1 will return 2.1. – krlzlx Jun 27 '17 at 15:05

Is it possible to have a custom decimal precision when returning JSON data?

2 Answers2