[Web API] Web API 2 深入系列(6) Model绑定(上)

2022-03-10 17:26:40

解决什么问题
Model元数据解析
- 复杂类型
ValueProvider
ValueProviderFactory

解决什么问题

Model： Action方法上的参数

Model绑定：对Action方法参数绑定

通过2个实例说明它的作用

定义控制器和特性路由

    [RoutePrefix("demo")]

    public class DemoController : ApiController

    {

        [Route("get/{x?}/{y?}/{z?}")]

        public IEnumerable<int> Get(int x, int y, int z)

        {

            yield return x;

            yield return y;

            yield return z;

        }

    }

SelfHost

    using (var server = new HttpSelfHostServer(new HttpSelfHostConfiguration("http://localhost:10000")))

    {

        server.Configuration.MapHttpAttributeRoutes();

        server.OpenAsync();

        Console.Read();

    }

请求地址:

请求结果,截图:

我们可以看到都返回了同样的结果,说明数据被绑定上了.

除了简单类型(基元类型和可空的值类型)支持绑定外,复杂类型也支持绑定.

    [Route("get2/{x}/{y}/{z}")]

    public Model Get(Model model)

    {

        return model;

    }

    [ModelBinder]

    public class Model

    {

        public string X { get; set; }

        public string Y { get; set; }

        public string Z { get; set; }

    }

请求地址:

路由地址

请求结果,截图:

同样成功绑定上!

补充:

查询参数的绑定优先级高于路由绑定

Model元数据解析

从上面的例子中,我们看到复杂类型同样能实现Model绑定.其依赖于Model元数据.

Model元数据不仅对复杂类型本身做描述,对复杂类型下的每个属性同样也有描述.

ModelMetadata则为Model元数据

public class ModelMetadata

{

    //类型

    public Type ModelType { get; }

    //是否复杂类型

    public virtual bool IsComplexType { get; }

    //是否可空类型

    public bool IsNullableValueType { get; }

    //父容器类型(root 为 null)

    public Type ContainerType { get; }

    //当前属性名

    public string PropertyName { get; }

    //当前属性值

    public object Model { get; set; }

    //所有子属性

    public virtual IEnumerable<ModelMetadata> Properties { get: }

}

复杂类型

IsComplexType判断是否为复杂类型

标准:是否允许字符串类型向该类型转换.

默认:基元类型和可空值类型

    public virtual bool IsComplexType

    {

      get { return !HasStringConverter(this.ModelType); }

    }

    internal static bool HasStringConverter(Type type)

    {

        //获取TypeConverter ,调用CanConvertFrom判断是否为复杂类型

      return TypeDescriptor.GetConverter(type).CanConvertFrom(typeof (string));

    }

定义一个TypeConverter

public class PointTypeConverter : TypeConverter

{

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)

    {

        if (value is string)

        {

            return ParsePoint(value as string);

        }

        return base.ConvertFrom(context, culture, value);

    }

    static Point ParsePoint(string value)

    {

        var point = new Point();

        var split = value.Split(',');

        point.X = double.Parse(split[0]);

        point.Y = double.Parse(split[1]);

        return point;

    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)

    {

        return sourceType == typeof(string);

    }

}

应用Point的TypeConverter 为 PointTypeConverter

[TypeConverter(typeof(PointTypeConverter))]

public class Point

{

    public double X { get; set; }

    public double Y { get; set; }

}

在DemoController加入一个Action

    [Route("get/{point}")]

    public Point Get(Point point)

    {

        return point;

    }

请求地址:

路由地址注意地址为1,2

Web API默认描述元数据类型为CachedDataAnnotationsModelMetadata

public class CachedDataAnnotationsModelMetadata : CachedModelMetadata<CachedDataAnnotationsMetadataAttributes>

{

}

//主要存储了Model上的特性

public class CachedDataAnnotationsMetadataAttributes

{

    public DisplayAttribute Display { get; protected set; }

    public DisplayNameAttribute DisplayName { get; protected set; }

    public DisplayFormatAttribute DisplayFormat { get; protected set; }

    public EditableAttribute Editable { get; protected set; }

    public ReadOnlyAttribute ReadOnly { get; protected set; }

    //从Model特性上赋值

    public CachedDataAnnotationsMetadataAttributes(IEnumerable<Attribute> attributes)

    {

        this.Display = attributes.OfType<DisplayAttribute>().FirstOrDefault<DisplayAttribute>();

        this.DisplayFormat = attributes.OfType<DisplayFormatAttribute>().FirstOrDefault<DisplayFormatAttribute>();

        this.DisplayName = attributes.OfType<DisplayNameAttribute>().FirstOrDefault<DisplayNameAttribute>();

        this.Editable = attributes.OfType<EditableAttribute>().FirstOrDefault<EditableAttribute>();

        this.ReadOnly = attributes.OfType<ReadOnlyAttribute>().FirstOrDefault<ReadOnlyAttribute>();

    }

}

补充:

Editable优先级高于ReadOnly

我们可以通过一个例子获取Model元数据

    //获取ModelMetadataProvider

    var provider = new HttpConfiguration().Services.GetModelMetadataProvider();

    foreach (CachedDataAnnotationsModelMetadata property in provider.GetMetadataForType(() => new Model { X = "1" }, typeof(Model)).Properties)

    {

        Console.WriteLine($"{property.GetDisplayName()}-{property.Model}-{property.ModelType}-{property.IsReadOnly}");

    }

运行截图:

ModelMetadataProvider

WebAPI利用ModelMetadataProvider 获取ModelMetadata

public abstract class ModelMetadataProvider

{

    //获取容器下所有属性元数据

    public abstract IEnumerable<ModelMetadata> GetMetadataForProperties(object container, Type containerType);

    //获取容器下指定属性元数据(modelAccessor 通过委托返回对象)

    public abstract ModelMetadata GetMetadataForProperty(Func<object> modelAccessor, Type containerType, string propertyName);

    //获取复杂数据的元数据

    public abstract ModelMetadata GetMetadataForType(Func<object> modelAccessor, Type modelType);

}

而WebAPI中默认的ModelMetadataProvider 为DataAnnotationsModelMetadataProvider,这也印证了上面的代码可行性

public class DataAnnotationsModelMetadataProvider : AssociatedMetadataProvider<CachedDataAnnotationsModelMetadata>

{

    //根据特性创建ModelMetadata

    protected override CachedDataAnnotationsModelMetadata CreateMetadataPrototype(IEnumerable<Attribute> attributes, Type containerType, Type modelType, string propertyName)

    {

      return new CachedDataAnnotationsModelMetadata(this, containerType, modelType, propertyName, attributes);

    }

    //根据原型创建ModelMetadata

    protected override CachedDataAnnotationsModelMetadata CreateMetadataFromPrototype(CachedDataAnnotationsModelMetadata prototype, Func<object> modelAccessor)

    {

      return new CachedDataAnnotationsModelMetadata(prototype, modelAccessor);

    }

}

ValueProvider

通过第1节,我们知道Model绑定的数据源有2个:路由和查询字符串.

ValueProvider可以视为数据源

IValueProvider

public interface IValueProvider

{

    //是否存在指定前缀

    bool ContainsPrefix(string prefix);

    //根据key 查找对应数据项

    ValueProviderResult GetValue(string key);

}

IEnumerableValueProvider

public interface IEnumerableValueProvider : IValueProvider

{

    //根据指定前缀 返回所有该前缀的key

    IDictionary<string, string> GetKeysFromPrefix(string prefix);

}

ValueProviderResult

public class ValueProviderResult

{

    //转换成字符串类型的值

    public string AttemptedValue { get; protected set; }

    //原始数据

    public object RawValue { get; protected set; }

    //类型转换 使用

    public CultureInfo Culture { get; protected set; }

    //类型转换

    public object ConvertTo(Type type)

    public virtual object ConvertTo(Type type, CultureInfo culture)

}

NameValuePairsValueProvider则是IEnumerableValueProvider的一个实现

public class NameValuePairsValueProvider : IEnumerableValueProvider, IValueProvider

{

    public virtual ValueProviderResult GetValue(string key)

    {

      object rawValue;

      if (this.Values.TryGetValue(key, out rawValue))

        return new ValueProviderResult(rawValue, string.Join(",", (IEnumerable<string>) rawValue), this._culture);

      return (ValueProviderResult) null;

    }

}

我们在本节开始已经说明Model绑定有2个数据来源,其对应的ValueProvider为

RouteDataValueProvider

public class RouteDataValueProvider : NameValuePairsValueProvider

{

    public RouteDataValueProvider(HttpActionContext actionContext, CultureInfo culture)

      : base(RouteDataValueProvider.GetRouteValues(actionContext.ControllerContext.RouteData), culture)

    {

    }

    internal static IEnumerable<KeyValuePair<string, string>> GetRouteValues(IHttpRouteData routeData)

    {

      foreach (KeyValuePair<string, object> keyValuePair in (IEnumerable<KeyValuePair<string, object>>) routeData.Values)

      {

        string value = keyValuePair.Value == null ? (string) null : keyValuePair.Value.ToString();

        yield return new KeyValuePair<string, string>(keyValuePair.Key, value);

      }

    }

}

QueryStringValueProvider

public class QueryStringValueProvider : NameValuePairsValueProvider

{

    public QueryStringValueProvider(HttpActionContext actionContext, CultureInfo culture)

        : base(actionContext.ControllerContext.Request.GetQueryNameValuePairs(), culture)

    {

    }

}

除了NameValuePairsValueProvider,Web API还定义了一个特殊的Provider

CompositeValueProvider 既是1个Provider 又是1个Provider集合

public class CompositeValueProvider : Collection<IValueProvider>, IEnumerableValueProvider, IValueProvider

{

    public CompositeValueProvider(IList<IValueProvider> list)

    //调用内部Provider集合

    public virtual ValueProviderResult GetValue(string key)

    //调用内部Provider集合

    public virtual IDictionary<string, string> GetKeysFromPrefix(string prefix)

}

ValueProviderFactory

ValueProvider是用来提供数据源的.Web API同时定义了ValueProviderFactory来创建ValueProvider

public abstract class ValueProviderFactory

{

    //根据HttpActionContext获取IValueProvider

    public abstract IValueProvider GetValueProvider(HttpActionContext actionContext);

}

同样,也有对应的RouteDataValueProviderFactory和QueryStringValueProviderFactory,另外,在这2个Factory中,做了同一次请求只创建一次的缓存处理.

对应的Web API也提供了CompositeValueProviderFactory

public class CompositeValueProviderFactory : ValueProviderFactory

{

    public CompositeValueProviderFactory(IEnumerable<ValueProviderFactory> factories)

    public override IValueProvider GetValueProvider(HttpActionContext actionContext)

    {

        //通过返回CompositeValueProvider来返回多个ValueProvider

        return (IValueProvider) new CompositeValueProvider(factories);

    }

}

通过ServicesContainer.GetValueProviderFactories()可以获取到HttpConfiguration注册的Factory.

而默认注册到ServicesContainer上的为DefaultServices

public DefaultServices(HttpConfiguration configuration)

{

    //由于QueryStringValueProviderFactory先注册,所以查询字符串的方式优先级高于路由数据

    this.SetMultiple<ValueProviderFactory>(new ValueProviderFactory[2]

    {

        (ValueProviderFactory) new QueryStringValueProviderFactory(),

        (ValueProviderFactory) new RouteDataValueProviderFactory()

    });

}

备注

文章中的代码并非完整WebAPI代码,一般是经过自己精简后的.
本篇内容使用MarkDown语法编辑
首发地址:http://neverc.cnblogs.com/p/6001891.html

码农公寓

解决什么问题

Model元数据解析

复杂类型

ValueProvider

ValueProviderFactory

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