ASP.NET 核心 MVC 默认模型值

Question

在我的应用程序中，我正在使用CQRS方法。对于一些查询，我写了IPagedRequest：

public interface IPagedRequest<out TResponse>: IRequest<TResponse> { 
int Page { get; set; } 
int PageSize { get; set; } 
}

我的问题是：如何全局设置页面和页面大小属性的默认值？我尝试使用IModelBinder，但我的代码不起作用：

public class PagedRequestBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
return typeof(IPagedRequest<object>).IsAssignableFrom(context.Metadata.ModelType)
? new PagedRequestBinder()
: null;
}
}
public class PagedRequestBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null)
{
throw new ArgumentNullException(nameof(bindingContext));
}
var pagedList = (IPagedRequest<object>) bindingContext.Model;
if (pagedList.Page == 0) pagedList.Page = 1;
if (pagedList.PageSize == 0) pagedList.PageSize = 25;
bindingContext.Result = ModelBindingResult.Success(pagedList);
return Task.CompletedTask;
}
}

Answer 1

对于将请求体绑定到模型，有两种类型，一种是通过[FromForm]从Form data绑定，另一种是通过[FromBody]application/json。

对于[FromForm]，它按IModelBinder绑定模型，对于FromBody，它使用JsonFormatter。

要[FromBody]操作，请尝试以下步骤：

1. 创建自定义 JSON 格式化程序

   public class CustomJsonInputFormatter : JsonInputFormatter
   {
   public CustomJsonInputFormatter(
   ILogger logger,
   JsonSerializerSettings serializerSettings,
   ArrayPool<char> charPool,
   ObjectPoolProvider objectPoolProvider,
   MvcOptions options,
   MvcJsonOptions jsonOptions) : base(logger, serializerSettings, charPool, objectPoolProvider, options, jsonOptions)
   {
   }
   public override async Task<InputFormatterResult> ReadRequestBodyAsync(InputFormatterContext context, Encoding encoding)
   {
   InputFormatterResult result = await base.ReadRequestBodyAsync(context, encoding);
   var pagedList = (IPagedRequest<object>)result.Model;
   if (pagedList != null)
   {
   if (pagedList.Page == 0) pagedList.Page = 1;
   if (pagedList.PageSize == 0) pagedList.PageSize = 25;
   }
   return result;
   }
   }
   

2. 注册 json 格式化程序

   services.AddMvc(options => {
   var serviceProvider = services.BuildServiceProvider();
   var customJsonInputFormatter = new CustomJsonInputFormatter(
   serviceProvider.GetRequiredService<ILoggerFactory>().CreateLogger<CustomJsonInputFormatter>(),
   serviceProvider.GetRequiredService<IOptions<MvcJsonOptions>>().Value.SerializerSettings,
   serviceProvider.GetRequiredService<ArrayPool<char>>(),
   serviceProvider.GetRequiredService<ObjectPoolProvider>(),
   options,
   serviceProvider.GetRequiredService<IOptions<MvcJsonOptions>>().Value
   );
   options.InputFormatters.Insert(0, customJsonInputFormatter);
   }).SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
   

3. 控制器

   [HttpPost]
   public ActionResult Test([FromBody]PagedRequest<Product> input)
   {
   return Ok(new PagedRequest<Product> {
   Page = 1,
   PageSize = 100
   });
   }