ASP.NET Core 请求/查询/响应参数格式转换（下划线命名）

业务场景：

在 ASP.NET Core 项目中，所有的代码都是骆驼命名，比如userName, UserName，但对于 WebApi 项目来说，因为业务需要，一些请求、查询和响应参数的格式需要转换，比如转换成下划线命名（又称为snake case），比如user_name。

具体实现：

请求和响应参数格式转换（请求具体是非get请求，响应参数一般为json），ASP.NET Core 实现很简单，Startup只需要下面配置代码：

public void ConfigureServices(IServiceCollection services)
{

    services.AddMvc()
    .AddJsonOptions(options => options.SerializerSettings.ContractResolver = new DefaultContractResolver()
    {
        NamingStrategy = new SnakeCaseNamingStrategy()
    });
}

查询参数实现比较麻烦点（具体为get请求，比如users?user_name=xishuai&user_id=1），实现代码：

public class RewriteQueryStringMiddleware
{
    private readonly RequestDelegate _next;

    //Your constructor will have the dependencies needed for database access
    public RewriteQueryStringMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        var query = context.Request.QueryString;
        if (query.HasValue)
        {
            var parms = string.Join("&", query.Value.TrimStart('?').Split('&').Select(s =>
            {
                var kv = s.Split('=');
                var k = kv[0].Replace("_", "");
                var v = kv[1];
                return $"{k}={v}";
            }));
            QueryString newQuery = new QueryString($"?{parms}");
            context.Request.QueryString = newQuery;
        }

        //Let the next middleware (MVC routing) handle the request
        //In case the path was updated, the MVC routing will see the updated path
        await _next.Invoke(context);
    }
}

public static class RewriteQueryStringExtensions
{
    public static IApplicationBuilder UseRewriteQueryString(this IApplicationBuilder builder)
    {
        return builder.UseMiddleware<RewriteQueryStringMiddleware>();
    }
}

实现原理就是截获请求，并对QueryString转换和重写，Startup中添加配置：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    app.UseRewriteQueryString();
}

参考资料：

• snake_case JSON with ASP.NET Core MVC
• Web Api Parameter binding: snake_case to camelCase
• Model binding in ASP.NET Core to map underscores to title case property names