解决方法：在Startup的ConfigureServices方法里加上下面的红色部分。
public IServiceProvider ConfigureServices(IServiceCollection services) { services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1).
AddJsonOptions(options => { options.SerializerSettings.ContractResolver = new DefaultContractResolver(); }); }
asp.net core mvc api 返回结果的json字段名大写小混乱的问题解决
原文：https://www.cnblogs.com/wjx-blog/p/10087072.html