将DisplayFormatAttribute.ConvertEmptyStringToNull的默认值设置为false

Question

我刚刚将一堆Web服务转换为Web API2.现在,当浏览器发送一个空字符串并且我输入的代码转换为null时,我的C#代码就会爆炸.我研究过全球解决方案,但没有找到我为我工作的解决方案.

我当然可以为我的所有Web API模型中的每个字符串手动设置它,但我有很多模型,所以更喜欢全局解决方案.

在这里:string.empty在将JSON对象传递给MVC Controller和其他页面时转换为null并尝试实现每个解决方案,但无济于事.

如何将ConvertEmptyStringToNull的默认值全局设置为false？

Answer 1

您需要将 替换为ModelMetadataProvider设置ConvertEmptyStringToNull为false

如：

public class EmptyStringAllowedModelMetadataProvider : DataAnnotationsModelMetadataProvider
{
    protected override CachedDataAnnotationsModelMetadata CreateMetadataFromPrototype(CachedDataAnnotationsModelMetadata prototype, Func<object> modelAccessor)
    {
        var metadata = base.CreateMetadataFromPrototype(prototype, modelAccessor);
        metadata.ConvertEmptyStringToNull = false;
        return metadata;
    }

    protected override CachedDataAnnotationsModelMetadata CreateMetadataPrototype(IEnumerable<Attribute> attributes, Type containerType, Type modelType, string propertyName)
    {
        var metadata = base.CreateMetadataPrototype(attributes, containerType, modelType, propertyName);
        metadata.ConvertEmptyStringToNull = false;
        return metadata;
    }
}

您将在您的 WebApiConfig 中注册，例如：

config.Services.Replace(typeof(ModelMetadataProvider), new EmptyStringAllowedModelMetadataProvider());

这是受https://gist.github.com/nakamura-to/4029706启发

Answer 2

您可以使用 Postsharp 尝试 Aspect 模式并在下面声明 Aspect。
它将适用于整个解决方案。为我工作。

using System;
using System.Linq;
using System.Reflection;
using Helpers.Aspects;
using PostSharp.Aspects;
using PostSharp.Extensibility;

[assembly: EmptyStringModelBindingAspect(
    AttributeTargetTypes = @"regex:[^\.]*\.Controllers\..*Controller",
    AttributeTargetTypeAttributes = MulticastAttributes.Public,
    AttributeTargetElements = MulticastTargets.Method,
    AttributeTargetMemberAttributes = MulticastAttributes.Public)]

namespace Helpers.Aspects
{
    [Serializable]
    public class EmptyStringModelBindingAspect : MethodInterceptionAspect
    {
        public override void OnInvoke(MethodInterceptionArgs args)
        {
            for (int i = 0; i < args.Arguments.Count; i++)
            {
                FixString(args, i);
                FixStringsInObjects(args.Arguments[i]);
            }

            args.Proceed();
        }

        private static void FixString(MethodInterceptionArgs args, int i)
        {
            if (args.Arguments[i] is string && args.Arguments[i] == null)
            {
                args.Arguments.SetArgument(i, string.Empty);
            }
        }

        private static void FixStringsInObjects(object obj)
        {
            if (obj == null)
            {
                return;
            }

            var type = obj.GetType();
            var properties = (from p in type.GetProperties() 
                                         let paramerers = p.GetIndexParameters() 
                                         where !paramerers.Any() 
                                         where p.PropertyType == typeof (string) && 
                                               p.CanRead && 
                                               p.CanWrite && 
                                               p.GetValue(obj, null) == null 
                                         select p).ToArray();

            foreach (var item in properties)
            {
                item.SetValue(obj, string.Empty, null);
            }
        }

        public override bool CompileTimeValidate(MethodBase method)
        {
            return !(method.Name.StartsWith("get_") || method.Name.StartsWith("set_"));
        }
    }
}