有没有人能够提供一个多态模型绑定的工作示例？我正在尝试使用这个示例（适用于Mvc而不是Api项目），但在API项目中无法运行。我认为在填充ValueProvider方面缺少一些步骤，但我找不到任何与此相关的资源（AspNet Core 3.1）。
我的尝试：
Dtos：
public abstract class Device
{
public string Kind { get; set; }
}
public class Laptop : Device
{
public string CPUIndex { get; set; }
}
public class SmartPhone : Device
{
public string ScreenSize { get; set; }
}
自定义模型绑定器实现：
public class DeviceModelBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context.Metadata.ModelType != typeof(Device))
{
return null;
}
var subclasses = new[] { typeof(Laptop), typeof(SmartPhone), };
var binders = new Dictionary<Type, (ModelMetadata, IModelBinder)>();
foreach (var type in subclasses)
{
var modelMetadata = context.MetadataProvider.GetMetadataForType(type);
binders[type] = (modelMetadata, context.CreateBinder(modelMetadata));
}
return new DeviceModelBinder(binders);
}
}
public class DeviceModelBinder : IModelBinder
{
private Dictionary<Type, (ModelMetadata, IModelBinder)> binders;
public DeviceModelBinder(Dictionary<Type, (ModelMetadata, IModelBinder)> binders)
{
this.binders = binders;
}
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
var modelKindName = ModelNames.CreatePropertyModelName(bindingContext.ModelName, nameof(Device.Kind));
var modelTypeValue = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
IModelBinder modelBinder;
ModelMetadata modelMetadata;
if (modelTypeValue.FirstValue == "Laptop")
{
(modelMetadata, modelBinder) = binders[typeof(Laptop)];
}
else if (modelTypeValue.FirstValue == "SmartPhone")
{
(modelMetadata, modelBinder) = binders[typeof(SmartPhone)];
}
else
{
bindingContext.Result = ModelBindingResult.Failed();
return;
}
var newBindingContext = DefaultModelBindingContext.CreateBindingContext(
bindingContext.ActionContext,
bindingContext.ValueProvider,
modelMetadata,
bindingInfo: null,
bindingContext.ModelName);
await modelBinder.BindModelAsync(newBindingContext);
bindingContext.Result = newBindingContext.Result;
if (newBindingContext.Result.IsModelSet)
{
// Setting the ValidationState ensures properties on derived types are correctly
bindingContext.ValidationState[newBindingContext.Result] = new ValidationStateEntry
{
Metadata = modelMetadata,
};
}
}
}
I register the model binder provider like so:
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers(o => o.ModelBinderProviders.Insert(0, new DeviceModelBinderProvider()));
}
然后我的控制器：
[ApiController]
[Route("test")]
public class TestController : ControllerBase
{
[HttpPost]
public IActionResult Test(Device dto)
{
var x = dto;
return Ok();
}
}
我要发送一个 JSON 请求体，类似这样：
{
"ScreenSize": "1",
"Kind": "SmartPhone"
}
这个文档真的让我感到很沮丧，因为其中涉及的魔法太多了。我的备选方案是手动解析请求中的HttpContent并反序列化。但是我希望能够像示例中一样使用模型绑定器方法。唯一奇怪的两件事是，bindingContext.ModelName为空，而bindingContext.ValueProvider仅包含一个路由值提供程序，其中包含action和controller键。所以，看起来请求正文甚至没有被解析成值提供程序。
