.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();
        }
    }
}