[Web API] Web API 2 深入系列(7) Model绑定(下)
目录
-
ModelBinder
-
ModelBinderProvider
-
不同类型的Model绑定
- 简单类型
- 复杂类型
- 其他类型
ModelBinder
ModelBinder是Model绑定的核心.
public interface IModelBinder
{
//绑定Model方法,返回绑定是否成功
bool BindModel(HttpActionContext actionContext, ModelBindingContext bindingContext);
}
ModelBindingContext
public class ModelBindingContext
{
//数据源
public IValueProvider ValueProvider { get; set; }
//最终创建的对象 绑定过程就是创建Model
public object Model { get; set; }
//参数名称
public string ModelName { get; set; }
//参数类型
public Type ModelType { get; }
//参数元数据
public ModelMetadata ModelMetadata { get; set; }
//属性元数据
public IDictionary<string, ModelMetadata> PropertyMetadata { get; }
//存储绑定结果(包括错误信息,ValueProviderResult),该值引用自ApiController的ModelState
public ModelStateDictionary ModelState { get; set; }
public bool FallbackToEmptyPrefix { get; set; }
}
当ModelBinder特性的Name(为null),FallbackToEmptyPrefix为True.
FallbackToEmptyPrefix为False时,则必须数据源有前缀才能绑定上.
Web API定义了一系列的ModelBinder,这里先介绍
public class CompositeModelBinder : IModelBinder
{
//IModelBinder 集合
public CompositeModelBinder(params IModelBinder[] binders)
//使用内部ModelBinder进行绑定Model(默认遍历一次,如果FallbackToEmptyPrefix为True,则会有2次遍历机会)
public virtual bool BindModel(HttpActionContext actionContext, ModelBindingContext bindingContext)
}
ModelBinderProvider
Web API通过ModelBinderProvider创建ModelBinder
public abstract class ModelBinderProvider
{
public abstract IModelBinder GetBinder(HttpConfiguration configuration, Type modelType);
}
Web API中默认注册了一系列的ModelBinderProvider
this.SetMultiple<ModelBinderProvider>(new ModelBinderProvider[8]
{
(ModelBinderProvider) new TypeConverterModelBinderProvider(),
(ModelBinderProvider) new TypeMatchModelBinderProvider(),
(ModelBinderProvider) new KeyValuePairModelBinderProvider(),
(ModelBinderProvider) new ComplexModelDtoModelBinderProvider(),
(ModelBinderProvider) new ArrayModelBinderProvider(),
(ModelBinderProvider) new DictionaryModelBinderProvider(),
(ModelBinderProvider) new CollectionModelBinderProvider(),
(ModelBinderProvider) new MutableObjectModelBinderProvider()
});
对应的我们先介绍一下
//同样都是组装一批ModelBinderProvider
public sealed class CompositeModelBinderProvider : ModelBinderProvider
{
public CompositeModelBinderProvider(IEnumerable<ModelBinderProvider> providers)
public override IModelBinder GetBinder(HttpConfiguration configuration, Type modelType)
}
ModelBinderAttribute除了通过Name设置FallbackToEmptyPrefix,还有个更重要的属性BinderType
public class ModelBinderAttribute : ParameterBindingAttribute
{
public string Name { get; set; }
//用来指定ModelBinder 或 ModelBinderProvider
public Type BinderType { get; set; }
}
不同类型的Model绑定
不同的数据类型,有不同的数据结构.
所以针对他们的绑定机制也是不同的.
简单类型
TypeConverterModelBinder
public sealed class TypeConverterModelBinder : IModelBinder
{
public bool BindModel(HttpActionContext actionContext, ModelBindingContext bindingContext)
{
ValueProviderResult valueProviderResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueProviderResult);
model = valueProviderResult.ConvertTo(bindingContext.ModelType);
bindingContext.Model = model;
return true;
}
}
复杂类型
在介绍复杂类型的Bind前,先介绍一下下面2个类型.
ComplexModelDto包含复杂类型的元数据和绑定结果
public class ComplexModelDto
{
public ComplexModelDto(ModelMetadata modelMetadata, IEnumerable<ModelMetadata> propertyMetadata)
public ModelMetadata ModelMetadata { get; private set; }
public Collection<ModelMetadata> PropertyMetadata { get; private set; }
//key 为属性的元数据,value 为绑定结果
public IDictionary<ModelMetadata, ComplexModelDtoResult> Results { get; private set; }
}
ComplexModelDtoResult
public sealed class ComplexModelDtoResult
{
//绑定结果值
public object Model { get; private set; }
//验证信息
public ModelValidationNode ValidationNode { get; private set; }
}
复杂类型的绑定由 MutableObjectModelBinder 和 ComplexModelDtoModelBinder共同完成.
而上面2个类型,实际就是用来在2个ModelBinder间传递的对象
public class MutableObjectModelBinder : IModelBinder
{
public virtual bool BindModel(HttpActionContext actionContext, ModelBindingContext bindingContext)
{
//类型筛选
if (!bindingContext.ValueProvider.ContainsPrefix(bindingContext.ModelName) || !MutableObjectModelBinder.CanBindType(bindingContext.ModelType))
return false;
//1. 创建空对象
bindingContext.ModelMetadata.Model = Activator.CreateInstance(bindingContext.ModelType);
//2. 创建ComplexModelDto对象
ComplexModelDto complexModelDto = new ComplexModelDto(bindingContext.ModelMetadata,bindingContext.PropertyMetadata);
//3. 进入绑定流程
this.ProcessDto(actionContext, bindingContext, complexModelDto);
return true;
}
internal void ProcessDto(HttpActionContext actionContext, ModelBindingContext bindingContext, ComplexModelDto dto)
{
//创建子ModelBindingContext
var subContext = new ModelBindingContext(bindingContext)
{
ModelName = bindingContext.ModelName,
ModelMetadata = GetMetadata(typeof(ComplexModelDto))
};
//调用ComplexModelDtoModelBinder 对ComplexModelDto进行绑定
actionContext.Bind(subContext);
//对复杂类型的属性进行绑定
foreach (var result in (IEnumerable<KeyValuePair<ModelMetadata, ComplexModelDtoResult>>) dto.Results)
{
ModelMetadata key = result.Key;
ComplexModelDtoResult dtoResult = result.Value;
if (dtoResult != null)
{
var property = bindingContext.ModelType.GetProperty(key.PropertyName);
this.SetProperty(actionContext, bindingContext, key, dtoResult,property);
}
}
}
}
ComplexModelDtoModelBinder则将所有属性再通过调度其他的ModelBinder进行绑定.并将结果保存在ComplexModelDto的Results属性中.
其他类型
Web API还提供了其他常用的数据类型 ModelBinder
CollectionModelBinder来实现 集合 类型(指的集合是实现了IEnumerable接口的类型)
ArrayModelBinder来实现 数组 类型
DictionaryModelBinder来实现 字典 类型
通过对应的ModelBinderProvider可以知道对应的ModelBinder 能实现哪种类型的绑定
备注
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文章中的代码并非完整WebAPI代码,一般是经过自己精简后的.
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本篇内容使用MarkDown语法编辑