为自定义类型创建自定义模型绑定器

Question

在ASP.NET CORE 1.1项目中,我有以下模型:

public class GetProductsModel {
  public OrderExpression OrderBy { get; set; }
}

OrderExpression是一个具有以下方法的类:

Boolean TryParse(String value, out OrderExpression expression)

该方法OrderExpression从a 创建一个实例String并可以使用:

OrderExpression expression;

Boolean parsed = OrderExpression.TryParse(value, out expression);

如何为类型属性创建自定义模型绑定器OrderExpression？

Answer 1

我假设在您的请求数据中有一个orderBy您想要绑定到OrderExpression使用的属性OrderExpression.TryParse.

我们假设你的OrderExpression类看起来如下,我提供了一个非常简单的TryParse方法实现:

public class OrderExpression
{
    public string RawValue { get; set; }
    public static bool TryParse(string value, out OrderExpression expr)
    {
        expr = new OrderExpression { RawValue = value };
        return true;
    }
}

然后你可以创建一个模型绑定器,它基本上获取原始字符串值并调用OrderExpression.TryParse:

public class OrderExpressionBinder : IModelBinder
{
    public Task BindModelAsync(ModelBindingContext bindingContext)
    {            
        var values = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if (values.Length == 0) return Task.CompletedTask;

        // Attempt to parse
        var stringValue = values.FirstValue;
        OrderExpression expression;
        if (OrderExpression.TryParse(stringValue, out expression))
        {
            bindingContext.ModelState.SetModelValue(bindingContext.ModelName, expression, stringValue);
            bindingContext.Result = ModelBindingResult.Success(expression);
        }

        return Task.CompletedTask;
    }
}

您还需要一个新的模型绑定程序提供程序,它只返回OrderExpression类型的新绑定程序:

public class OrderExpressionBinderProvider : IModelBinderProvider
{
    public IModelBinder GetBinder(ModelBinderProviderContext context)
    {
        return context.Metadata.ModelType == typeof(OrderExpression) ? new OrderExpressionBinder() : null;
    }
}

// It should be registered in your Startup class, adding it to the ModelBinderProviders collection:
services.AddMvc(opts => {
    opts.ModelBinderProviders.Insert(0, new OrderExpressionBinderProvider());
});

有了这个,您将能够绑定OrderExpression控制器操作的参数.类似于以下示例中的内容:

[HttpPost]
public IActionResult Products([FromBody]OrderExpression orderBy) 
{
    return Ok();
}

$.ajax({
    method: 'POST', 
    dataType: 'json', 
    url: '/home/products', 
    data: {orderby: 'my orderby expression'}
});

但是,还需要做一些事情才能发送json并将其绑定到GetProductsModel内部包含的复杂模型OrderExpression.我在谈论这样的场景:

[HttpPost]
public IActionResult Products([FromBody]GetProductsModel model)
{
    return Ok();
}

public class GetProductsModel
{
    public OrderExpression OrderBy { get; set; }
}

$.ajax({
    method: 'POST', 
    dataType: 'json', 
    contentType: 'application/json; charset=utf-8', 
    url: '/home/products', 
    data: JSON.stringify({orderby: 'my orderby expression'})
});

在那种情况下,ASP.Net Core将使用Newtonsoft.Json作为InputFormatter并将接收到的json转换为GetProductsModel模型的实例,而不尝试将new OrderExpressionBinderProvider用于内部属性.

幸运的是,您还可以OrderExpression通过创建JsonConverter 告诉Newtonsoft.Json如何格式化类型的属性:

public class OrderExpressionJsonConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(OrderExpression);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var stringValue = reader.Value?.ToString();
        OrderExpression expression;
        if (OrderExpression.TryParse(stringValue, out expression))
        {
            return expression;
        }
        return null;
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

哪个应该在您的Startup类中注册:

services.AddMvc(opts => {
    opts.ModelBinderProviders.Insert(0, new OrderExpressionBinderProvider());

}).AddJsonOptions(opts => {
    opts.SerializerSettings.Converters.Add(new OrderExpressionJsonConverter());
});

现在你终于可以处理这两种情况:)