Asp网核rc2.抽象类模型绑定

Question

在RC1中,我使用以下代码进行抽象类或接口绑定:

public class MessageModelBinder : IModelBinder {

    public Task<ModelBindingResult> BindModelAsync(ModelBindingContext bindingContext) {
        if(bindingContext.ModelType == typeof(ICommand)) {
            var msgTypeResult = bindingContext.ValueProvider.GetValue("messageType");
            if(msgTypeResult == ValueProviderResult.None) {
                return ModelBindingResult.FailedAsync(bindingContext.ModelName);
            }
            var type = Assembly.GetAssembly(typeof(MessageModelBinder )).GetTypes().SingleOrDefault(t => t.FullName == msgTypeResult.FirstValue);
            if(type == null) {
                return ModelBindingResult.FailedAsync(bindingContext.ModelName);
            }
            var metadataProvider = (IModelMetadataProvider)bindingContext.OperationBindingContext.HttpContext.RequestServices.GetService(typeof(IModelMetadataProvider));
            bindingContext.ModelMetadata = metadataProvider.GetMetadataForType(type);
        }
        return ModelBindingResult.NoResultAsync;
    }
}

此绑定程序仅从messageType查询字符串中读取模型类型(参数)并覆盖元数据类型.其余的工作由标准粘合剂执行,如BodyModelBinder.

在Startup.cs中我只添加第一个binder:

services.AddMvc().Services.Configure<MvcOptions>(options => {
    options.ModelBinders.Insert(0, new MessageModelBinder());
});

控制器:

[Route("api/[controller]")]
public class MessageController : Controller {
    [HttpPost("{messageType}")]
    public ActionResult Post(string messageType, [FromBody]ICommand message) {
    } 
}

我怎样才能在RC2中执行此操作？

据我了解,现在我必须使用IModelBinderProvider.好的,我试过了.Startup.cs:

services.AddMvc().Services.Configure<MvcOptions>(options => {
    options.ModelBinderProviders.Insert(0, new MessageModelBinderProvider());
});

ModelBinderProvider:

public class MessageModelBinderProvider : IModelBinderProvider {
    public IModelBinder GetBinder(ModelBinderProviderContext context) {
        if(context == null) {
            throw new ArgumentNullException(nameof(context));
        }
        return context.Metadata.ModelType == typeof(ICommand) ? new MessageModelBinder() : null;
    }
}

ModelBinder的:

public class MessageModelBinder : IModelBinder {
    public Task BindModelAsync(ModelBindingContext bindingContext) {
        if(bindingContext.ModelType == typeof(ICommand)) {
            var msgTypeResult = bindingContext.ValueProvider.GetValue("messageType");
            if(msgTypeResult == ValueProviderResult.None) {
                bindingContext.Result = ModelBindingResult.Failed(bindingContext.ModelName);
                return Task.FromResult(0);
            }
            var type = typeof(MessageModelBinder).GetTypeInfo().Assembly.GetTypes().SingleOrDefault(t => t.FullName == msgTypeResult.FirstValue);
            if(type == null) {
                bindingContext.Result = ModelBindingResult.Failed(bindingContext.ModelName);
                return Task.FromResult(0);
            }
            var metadataProvider = (IModelMetadataProvider)bindingContext.OperationBindingContext.HttpContext.RequestServices.GetService(typeof(IModelMetadataProvider));
            bindingContext.ModelMetadata = metadataProvider.GetMetadataForType(type);
            bindingContext.Result = ModelBindingResult.Success(bindingContext.ModelName, Activator.CreateInstance(type));
        }
        return Task.FromResult(0);
    }
}

但我无法指明NoResult.如果我没有指定bindingContext.Result,我在控制器中得到null模型.如果我指定bindingContext.Result,我得到空模型而不设置模型字段.

Answer 1

我对自定义模型绑定和抽象类有类似的要求， dougbu在 github AspNet/Mvc/issues/4703上发布的建议对我有用。我从RC1升级到ASP.NET Core 1.0，需要根据他的建议修改我的自定义模型绑定器。我已经复制并粘贴了他的代码，以防 github 问题的链接中断。阅读 github 问题中的评论，了解有关在服务器上创建请求类型的对象的代码的安全注意事项。

消息模型绑定器提供者

public class MessageModelBinderProvider : IModelBinderProvider 
{
    public IModelBinder GetBinder(ModelBinderProviderContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        if (context.Metadata.ModelType != typeof(ICommand))
        {
            return null;
        }

        var binders = new Dictionary<string, IModelBinder>();
        foreach (var type in typeof(MessageModelBinderProvider).GetTypeInfo().Assembly.GetTypes())
        {
            var typeInfo = type.GetTypeInfo();
            if (typeInfo.IsAbstract || typeInfo.IsNested)
            {
                continue;
            }

            if (!(typeInfo.IsClass && typeInfo.IsPublic))
            {
                continue;
            }

            if (!typeof(ICommand).IsAssignableFrom(type))
            {
                continue;
            }

            var metadata = context.MetadataProvider.GetMetadataForType(type);
            var binder = context.CreateBinder(metadata);
            binders.Add(type.FullName, binder);
        }

        return new MessageModelBinder(context.MetadataProvider, binders);
    }
}

消息模型绑定器

public class MessageModelBinder : IModelBinder
{
    private readonly IModelMetadataProvider _metadataProvider;
    private readonly Dictionary<string, IModelBinder> _binders;

    public MessageModelBinder(IModelMetadataProvider metadataProvider, Dictionary<string, IModelBinder> binders)
    {
        _metadataProvider = metadataProvider;
        _binders = binders;
    }

    public async Task BindModelAsync(ModelBindingContext bindingContext)
    {
        var messageTypeModelName = ModelNames.CreatePropertyModelName(bindingContext.ModelName, "messageType");
        var messageTypeResult = bindingContext.ValueProvider.GetValue(messageTypeModelName);
        if (messageTypeResult == ValueProviderResult.None)
        {
            bindingContext.Result = ModelBindingResult.Failed();
            return;
        }

        IModelBinder binder;
        if (!_binders.TryGetValue(messageTypeResult.FirstValue, out binder))
        {
            bindingContext.Result = ModelBindingResult.Failed();
            return;
        }

        // Now know the type exists in the assembly.
        var type = Type.GetType(messageTypeResult.FirstValue);
        var metadata = _metadataProvider.GetMetadataForType(type);

        ModelBindingResult result;
        using (bindingContext.EnterNestedScope(metadata, bindingContext.FieldName, bindingContext.ModelName, model: null))
        {
            await binder.BindModelAsync(bindingContext);
            result = bindingContext.Result;
        }

        bindingContext.Result = result;
    }
}