WebApi result lost decimal property's precision?

[Rorschach331]

use the simple web api template:

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.MapGet("/weatherforecast", () =>
    {
        var forecast = new WeatherForecast
        (
            19493.7797202797203M
        );
        return forecast;
    })
    .WithName("GetWeatherForecast")
    .WithOpenApi();

app.Run();
record WeatherForecast(decimal Amount)
{
   
}

when i call the api in the swagger,i get a json like this:

{
  "amount": 19493.77972027972
}

the amount value is 19493.77972027972,but i want the value 19493.7797202797203,what should i do?

[engineering87]

Hello @Rorschach331,
to preserve the full precision, you can work around return it as a string.
If you need it to remain a number, you'll have to write a custom JsonConverter for decimal to control the formatting:

public class DecimalJsonConverter : JsonConverter<decimal>
{
    public override decimal Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
        => reader.GetDecimal();

    public override void Write(Utf8JsonWriter writer, decimal value, JsonSerializerOptions options)
    {
        writer.WriteRawValue(value.ToString("G29", System.Globalization.CultureInfo.InvariantCulture));
    }
}

In your Program.cs:

builder.Services.Configure<Microsoft.AspNetCore.Http.Json.JsonOptions>(options =>
{
    options.SerializerOptions.Converters.Add(new DecimalJsonConverter());
});

and use:

record WeatherForecast(decimal Amount);

app.MapGet("/weatherforecast", () =>
{
    var forecast = new WeatherForecast(19493.7797202797203M);
    return forecast;
});

Try and let me know.

[Rorschach331]

Thank you for your reply.
My solution at the time was to return a string to the front-end.
I tested the DecimalJsonConverter and it worked fine.
However, I think this issue is caused by JavaScript Number type. To correctly handle high-precision numbers, the front-end needs to reference a library like decimal.js.