.NET JSON naiming style attribute. A action attribute that converts JSON columns naming style.

JsonCamelCaseAttribute.cs

using System;
using System.Text.Json;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;

namespace Demo.Attributes
{
    public class JsonCamelCase : Attribute, IResultFilter
    {
        private bool IsLowerCamelCase { get; }

        public JsonCamelCase(bool isLowerCamelCase)
        {
            IsLowerCamelCase = isLowerCamelCase;
        }

        public void OnResultExecuted(ResultExecutedContext context)
        {
        }

        public void OnResultExecuting(ResultExecutingContext context)
        {
            try
            {
                if (context.Result is JsonResult jsonResult)
                {
                    var options = new JsonSerializerOptions();
                    if (jsonResult.SerializerSettings != null)
                    {
                        options = jsonResult.SerializerSettings as JsonSerializerOptions;
                    }
                    options.PropertyNamingPolicy = IsLowerCamelCase ? JsonNamingPolicy.CamelCase : null;

                    jsonResult.SerializerSettings = options;
                }
            }
            catch (Exception)
            {
                // ignored
            }
        }
    }

}