.netcore2.1 统一接口返回属性名称

　　为了开发规范，有时需要统一响应属性名称，.netcore已为我们封装好了，我们直接用即可。

　　在StartUp类中ConfigureServices方法中，添加如下代码：

 public void ConfigureServices(IServiceCollection services)
        {
          
            services.AddMvc()
            .AddJsonOptions(opt =>
            {
                // opt.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();//原样输出，后台属性怎么写的，返回的 json 就是怎样的

               // opt.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.CamelCasePropertyNamesContractResolver();//驼峰命名法，首字母小写

                opt.SerializerSettings.ContractResolver =new LowercaseContractResolver();//自定义扩展，属性全为小写
            })
            .SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

　　自定义全部小写扩展类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace MyApi.Common.Extension
{
    public class LowercaseContractResolver: Newtonsoft.Json.Serialization.DefaultContractResolver
    {
        protected override string ResolvePropertyName(string propertyName)
        {
            return propertyName.ToLower();
        }
    }
}