ASP.NET Core MVC中所提供的Model Binding功能简单但实用,其主要目的是将请求中包含的数据映射到action的方法参数中。这样就避免了开发者像在Web Forms时代那样需要从Request类中手动获取数据的繁锁操作,直接提高了开发效率。此功能继承自ASP.NET MVC,所以熟悉上一代框架开发的工程师,可以毫无障碍地继续享有它的便利。
本文想要探索下Model Binding相关的内容,这里先从源码中找到其发生的时机与场合。
在ControllerActionInvoker类的Next方法内部,可以看到对BindArgumentsAsync方法的调用,这里即会对方法的参数进行绑定数据的处理。
private Task Next(ref State next, ref Scope scope, ref object state, ref bool isCompleted){ switch (next) { case State.ActionBegin: { var controllerContext = _controllerContext; _cursor.Reset(); _instance = _cacheEntry.ControllerFactory(controllerContext); _arguments = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase); var task = BindArgumentsAsync(); if (task.Status != TaskStatus.RanToCompletion) { next = State.ActionNext; return task; } goto case State.ActionNext; } ... } }
此方法又调用了ControllerActionInvokerCacheEntry类中ControllerBinderDelegate属性,该属性是一个delegate方法,所以传入参数后可直接执行处理。
private Task BindArgumentsAsync(){ ... return _cacheEntry.ControllerBinderDelegate(_controllerContext, _instance, _arguments); }
创建ControllerActionInvokerCacheEntry的地方是前两篇文章(Controller,Action)中已经提到过的ControllerActionInvokerCache类。
public (ControllerActionInvokerCacheEntry cacheEntry, IFilterMetadata[] filters) GetCachedResult(ControllerContext controllerContext) { ... if (!cache.Entries.TryGetValue(actionDescriptor, out var cacheEntry)) { ... var propertyBinderFactory = ControllerBinderDelegateProvider.CreateBinderDelegate( _parameterBinder, _modelBinderFactory, _modelMetadataProvider, actionDescriptor); var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor); cacheEntry = new ControllerActionInvokerCacheEntry( filterFactoryResult.CacheableFilters, controllerFactory, controllerReleaser, propertyBinderFactory, objectMethodExecutor, actionMethodExecutor); cacheEntry = cache.Entries.GetOrAdd(actionDescriptor, cacheEntry); } ... return (cacheEntry, filters); }
于是跟踪至ControllerBinderDelegateProvider类,找到CreateBinderDelegate方法。
public static ControllerBinderDelegate CreateBinderDelegate( ParameterBinder parameterBinder, IModelBinderFactory modelBinderFactory, IModelMetadataProvider modelMetadataProvider, ControllerActionDescriptor actionDescriptor){ ... var parameterBindingInfo = GetParameterBindingInfo(modelBinderFactory, modelMetadataProvider, actionDescriptor); ... return Bind; async Task Bind(ControllerContext controllerContext, object controller, Dictionary<string, object> arguments) { var valueProvider = await CompositeValueProvider.CreateAsync(controllerContext); var parameters = actionDescriptor.Parameters; for (var i = 0; i < parameters.Count; i++) { var parameter = parameters[i]; var bindingInfo = parameterBindingInfo[i]; var modelMetadata = bindingInfo.ModelMetadata; if (!modelMetadata.IsBindingAllowed) { continue; } var result = await parameterBinder.BindModelAsync( controllerContext, bindingInfo.ModelBinder, valueProvider, parameter, modelMetadata, value: null); if (result.IsModelSet) { arguments[parameter.Name] = result.Model; } } ... } }
这里可以看到创建绑定的delegate方法,与之对应的是之前那句_cacheEntry.ControllerBinderDelegate(_controllerContext, _instance, _arguments)
代码。
public virtual async Task<ModelBindingResult> BindModelAsync( ActionContext actionContext, IModelBinder modelBinder, IValueProvider valueProvider, ParameterDescriptor parameter, ModelMetadata metadata, object value){ ... var modelBindingContext = DefaultModelBindingContext.CreateBindingContext( actionContext, valueProvider, metadata, parameter.BindingInfo, parameter.Name); modelBindingContext.Model = value; ... await modelBinder.BindModelAsync(modelBindingContext); ... var modelBindingResult = modelBindingContext.Result; ... return modelBindingResult; }
到了此处,就是旅程的终点。ParameterBinder类的BindModelAsync中可以找到对IModelBinder类型的BindModelAsync方法的调用。Model Binding这一操作便是在此时此地实现的。
接下来的疑问有两处,modelBinder是如何产生的,请求中的数据又是怎样与modelBinder发生联系。
ModelBinder
回到ControllerBinderDelegateProvider类的CreateBinderDelegate方法,可以看到其中调用了GetParameterBindingInfo方法。
private static BinderItem[] GetParameterBindingInfo( IModelBinderFactory modelBinderFactory, IModelMetadataProvider modelMetadataProvider, ControllerActionDescriptor actionDescriptor) { var parameters = actionDescriptor.Parameters; ... var parameterBindingInfo = new BinderItem[parameters.Count]; for (var i = 0; i < parameters.Count; i++) { var parameter = parameters[i]; ... var binder = modelBinderFactory.CreateBinder(new ModelBinderFactoryContext { BindingInfo = parameter.BindingInfo, Metadata = metadata, CacheToken = parameter, }); parameterBindingInfo[i] = new BinderItem(binder, metadata); } return parameterBindingInfo; }
这里的代码很明显地说明了modelBinder由ModelBinderFactory类的CreateBinder方法创建。
public IModelBinder CreateBinder(ModelBinderFactoryContext context){ ... IModelBinder binder; if (TryGetCachedBinder(context.Metadata, context.CacheToken, out binder)) { return binder; } var providerContext = new DefaultModelBinderProviderContext(this, context); binder = CreateBinderCoreUncached(providerContext, context.CacheToken); ... AddToCache(context.Metadata, context.CacheToken, binder); return binder; }
CreateBinder方法内部中如果缓存可以取到值,则从缓存内取值并直接返回,否则通过CreateBinderCoreUncached方法取值。
private IModelBinder CreateBinderCoreUncached(DefaultModelBinderProviderContext providerContext, object token){ ... IModelBinder result = null; for (var i = 0; i < _providers.Length; i++) { var provider = _providers[i]; result = provider.GetBinder(providerContext); if (result != null) { break; } } ... return result; }
这里的providers集合又包含哪些数据呢?可以从MvcCoreMvcOptionsSetup类中找到答案。
public void Configure(MvcOptions options){ // Set up ModelBinding options.ModelBinderProviders.Add(new BinderTypeModelBinderProvider()); options.ModelBinderProviders.Add(new ServicesModelBinderProvider()); options.ModelBinderProviders.Add(new BodyModelBinderProvider(options.InputFormatters, _readerFactory, _loggerFactory, options)); options.ModelBinderProviders.Add(new HeaderModelBinderProvider()); options.ModelBinderProviders.Add(new FloatingPointTypeModelBinderProvider()); options.ModelBinderProviders.Add(new EnumTypeModelBinderProvider(options)); options.ModelBinderProviders.Add(new SimpleTypeModelBinderProvider()); options.ModelBinderProviders.Add(new CancellationTokenModelBinderProvider()); options.ModelBinderProviders.Add(new ByteArrayModelBinderProvider()); options.ModelBinderProviders.Add(new FormFileModelBinderProvider()); options.ModelBinderProviders.Add(new FormCollectionModelBinderProvider()); options.ModelBinderProviders.Add(new KeyValuePairModelBinderProvider()); options.ModelBinderProviders.Add(new DictionaryModelBinderProvider()); options.ModelBinderProviders.Add(new ArrayModelBinderProvider()); options.ModelBinderProviders.Add(new CollectionModelBinderProvider()); options.ModelBinderProviders.Add(new ComplexTypeModelBinderProvider()); ... }
以上便是.NET Core MVC中所有被框架支持的ModelBinderProvider。
以一个最典型的FormCollectionModelBinderProvider为例。它以Metadata.ModelType的类型作为判断依据,如果是IFormCollection类型的话,则返回一个FormCollectionModelBinder对象。
public IModelBinder GetBinder(ModelBinderProviderContext context){ ... var modelType = context.Metadata.ModelType; ... if (modelType == typeof(IFormCollection)) { var loggerFactory = context.Services.GetRequiredService<ILoggerFactory>(); return new FormCollectionModelBinder(loggerFactory); } return null; }
在CreateBinderCoreUncached方法的循环体内部会依次尝试ModelBinderProvider们是否能创建合适的ModelBinder,一旦能够生成ModelBinder,则跳出当前循环,以这个对象作为返回值。
ValueProvider
有了ModelBinder,还需要有数据才能进行绑定。而为ModelBinder提供数据的是一些ValueProvider。
MvcCoreMvcOptionsSetup类的Configure方法里,再往下找,可以看到ValueProvider们的踪影。更确切地是与之对应的工厂类们。
public void Configure(MvcOptions options){ ... // Set up ValueProviders options.ValueProviderFactories.Add(new FormValueProviderFactory()); options.ValueProviderFactories.Add(new RouteValueProviderFactory()); options.ValueProviderFactories.Add(new QueryStringValueProviderFactory()); options.ValueProviderFactories.Add(new JQueryFormValueProviderFactory()); ... }
以FormValueProviderFactory为例,看一下其内部:
public Task CreateValueProviderAsync(ValueProviderFactoryContext context){ ... var request = context.ActionContext.HttpContext.Request; if (request.HasFormContentType) { // Allocating a Task only when the body is form data. return AddValueProviderAsync(context); } return Task.CompletedTask; }private static async Task AddValueProviderAsync(ValueProviderFactoryContext context){ var request = context.ActionContext.HttpContext.Request; var valueProvider = new FormValueProvider( BindingSource.Form, await request.ReadFormAsync(), CultureInfo.CurrentCulture); context.ValueProviders.Add(valueProvider); }
通过CreateValueProviderAsync方法可以得到一个FormValueProvider对象。
而这些ValueProviderFactory所创建的ValueProvider又统一被CompositeValueProvider类的CreateAsync方法聚合成CompositeValueProvider这个集合对象的内部元素。
public static async Task<CompositeValueProvider> CreateAsync( ActionContext actionContext, IList<IValueProviderFactory> factories){ var valueProviderFactoryContext = new ValueProviderFactoryContext(actionContext); for (var i = 0; i < factories.Count; i++) { var factory = factories[i]; await factory.CreateValueProviderAsync(valueProviderFactoryContext); } return new CompositeValueProvider(valueProviderFactoryContext.ValueProviders); }
再到ControllerBinderDelegateProvider类的CreateBinderDelegate方法中,找到valueProvider创建的起始点。
async Task Bind(ControllerContext controllerContext, object controller, Dictionary<string, object> arguments){ var valueProvider = await CompositeValueProvider.CreateAsync(controllerContext); var parameters = actionDescriptor.Parameters; for (var i = 0; i < parameters.Count; i++) { var parameter = parameters[i]; var bindingInfo = parameterBindingInfo[i]; var modelMetadata = bindingInfo.ModelMetadata; if (!modelMetadata.IsBindingAllowed) { continue; } var result = await parameterBinder.BindModelAsync( controllerContext, bindingInfo.ModelBinder, valueProvider, parameter, modelMetadata, value: null); if (result.IsModelSet) { arguments[parameter.Name] = result.Model; } } ... }
所得到的valueProvider在ParameterBinder类的BindModelAsync方法里还要再作进一步的处理。先作为参数传入创建DefaultModelBindingContext的方法:
var modelBindingContext = DefaultModelBindingContext.CreateBindingContext( actionContext, valueProvider, metadata, parameter.BindingInfo, parameter.Name);
再对ValueProvider作过滤处理:
return new DefaultModelBindingContext() { ActionContext = actionContext, BinderModelName = binderModelName, BindingSource = bindingSource, PropertyFilter = propertyFilterProvider?.PropertyFilter, // Because this is the top-level context, FieldName and ModelName should be the same. FieldName = binderModelName ?? modelName, ModelName = binderModelName ?? modelName, IsTopLevelObject = true, ModelMetadata = metadata, ModelState = actionContext.ModelState, OriginalValueProvider = valueProvider, ValueProvider = FilterValueProvider(valueProvider, bindingSource), ValidationState = new ValidationStateDictionary(), };
FilterValueProvider方法最终会调用CompositeValueProvider类的Filter方法,以得到所有合适的valueProvider。
public IValueProvider Filter(BindingSource bindingSource){ ... var filteredValueProviders = new List<IValueProvider>(); foreach (var valueProvider in this.OfType<IBindingSourceValueProvider>()) { var result = valueProvider.Filter(bindingSource); if (result != null) { filteredValueProviders.Add(result); } } ... return new CompositeValueProvider(filteredValueProviders); }
那么当在ModelBinder的BindModelAsync方法里需要获取数据时,以FloatModelBinder为例:
public Task BindModelAsync(ModelBindingContext bindingContext){ ... var modelName = bindingContext.ModelName; var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName); ... }
会试图从已过滤的ValueProvider中获取值。这时还是利用了CompositeValueProvider类中的方法。
public virtual ValueProviderResult GetValue(string key){ // Performance-sensitive // Caching the count is faster for IList<T> var itemCount = Items.Count; for (var i = 0; i < itemCount; i++) { var valueProvider = Items[i]; var result = valueProvider.GetValue(key); if (result != ValueProviderResult.None) { return result; } } return ValueProviderResult.None; }
这里的逻辑是从valueProvider集合中逐一尝试取值,有数据的则直接返回。
这也意味着数据绑定会以FormValueProvider到RouteValueProvider,再到QueryStringValueProvider,最后向JQueryFormValueProvider取值,这一流程执行,中间如果有任何一个能得到数据的话,则不再继续访问后面的ValueProvider。当然,前提是这些ValueProvider要不被先前的过滤处理排除在外。
若是还不明白这一顺序关系的话,可以回想下从ValueProviderFactories的添加顺序,再至ValueProvider集合生成时各个ValueProvider的顺序,就比较容易了解其中道理了。
原文出处:https://www.cnblogs.com/kenwoo/p/9514817.html
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