实体框架 – 我们如何使用Breeze的本地时区生存

当实体框架从数据库中获取DateTime值时,将其设置为DateTimeKind.Unspecified.换句话说,本地或UTC.我们特意将日期标记为DateTimeKind.Local.

为了实现这一点,我们决定调整实体框架的生成实体类的模板.而不是我们的日期是一个简单的属性,我们引入了一个后台存储日期,并使用属性设置器将日期设置为本地,如果它是未指定的.

在模板(.tt文件)中,我们更换了…

public string Property(EdmProperty edmProperty)
{
    return string.Format(
        CultureInfo.InvariantCulture,"{0} {1} {2} {{ {3}get; {4}set; }}",Accessibility.ForProperty(edmProperty),_typeMapper.GetTypeName(edmProperty.TypeUsage),_code.Escape(edmProperty),_code.SpaceAfter(Accessibility.ForGetter(edmProperty)),_code.SpaceAfter(Accessibility.ForSetter(edmProperty)));
}

…与…

public string Property(EdmProperty edmProperty)
{
    // Customised DateTime property handler to default DateKind to local time
    if (_typeMapper.GetTypeName(edmProperty.TypeUsage).Contains("DateTime")) {
        return string.Format(
            CultureInfo.InvariantCulture,"private {1} _{2}; {0} {1} {2} {{ {3}get {{ return _{2}; }} {4}set {{ _{2} = DateKindHelper.DefaultToLocal(value); }}}}",_code.SpaceAfter(Accessibility.ForSetter(edmProperty)));
    } else {
        return string.Format(
            CultureInfo.InvariantCulture,_code.SpaceAfter(Accessibility.ForSetter(edmProperty)));
    }
}

这造成了一个相当丑陋的一线设置者,但它完成了工作.它使用帮助函数将日期默认为本地,如下所示：

public class DateKindHelper
{
    public static DateTime DefaultToLocal(DateTime date)
    {
        return date.Kind == DateTimeKind.Unspecified ? DateTime.SpecifyKind(date,DateTimeKind.Local) : date;
    }

    public static DateTime? DefaultToLocal(DateTime? date)
    {
        return date.HasValue && date.Value.Kind == DateTimeKind.Unspecified ? DateTime.SpecifyKind(date.Value,DateTimeKind.Local) : date;
    }
}

我们的解决方案第2部分：IQueryable过滤器

下一个问题是Breeze在将where子句应用于IQueryable控制器操作时通过UTC日期.在审查了Breeze,Web API和实体框架的代码后,我们决定最好的选择是拦截对我们的控制器操作的调用,并在本地日期的QueryString中交换UTC日期.

我们选择使用我们可以应用于我们的控制器操作的自定义属性来执行此操作,例如：

[UseLocalTime]
public IQueryable<Product> Products()
{
    return _dc.Context.Products;
}

实现此属性的类是：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http;
using System.Web.Http.Filters;
using System.Text.RegularExpressions;
using System.Xml;

namespace TestBreeze.Controllers.api
{
    public class UseLocalTimeAttribute : ActionFilterAttribute
    {
        Regex isoRegex = new Regex(@"((?:-?(?:[1-9][0-9]*)?[0-9]{4})-(?:1[0-2]|0[1-9])-(?:3[0-1]|0[1-9]|[1-2][0-9])T(?:2[0-3]|[0-1][0-9]):(?:[0-5][0-9]):(?:[0-5][0-9])(?:.[0-9]+)?Z)",RegexOptions.IgnoreCase);

        public override void OnActionExecuting(System.Web.Http.Controllers.HttpActionContext actionContext)
        {
            // replace all ISO (UTC) dates in the query string with local dates
            var uriString = HttpUtility.UrlDecode(actionContext.Request.RequestUri.OriginalString);
            var matches = isoRegex.Matches(uriString);
            if (matches.Count > 0)
            {
                foreach (Match match in matches)
                {
                    var localTime = XmlConvert.ToDateTime(match.Value,XmlDateTimeSerializationMode.Local);
                    var localString = XmlConvert.ToString(localTime,XmlDateTimeSerializationMode.Local);
                    var encoded = HttpUtility.UrlEncode(localString);
                    uriString = uriString.Replace(match.Value,encoded);
                }
                actionContext.Request.RequestUri = new Uri(uriString);
            }

            base.OnActionExecuting(actionContext);
        }
    }
}

我们的解决方案第3部分：Json

这可能更有争议,但是我们的网络应用程序受众也完全是本地的:).

我们希望Json默认发送到客户端以包含本地时区的日期/时间.此外,我们还希望从客户端收到的Json中的任何日期转换为本地时区.为此,我们创建了一个自定义的JsonLocalDateTimeConverter并交换出了Json转换器Breeze的安装.

转换器如下所示：

public class JsonLocalDateTimeConverter : IsoDateTimeConverter
{
    public JsonLocalDateTimeConverter () : base() 
    {
        // Hack is for the issue described in this post (copied from BreezeConfig.cs):
        // https://stackoverflow.com/questions/11789114/internet-explorer-json-net-javascript-date-and-milliseconds-issue
        DateTimeFormat = "yyyy-MM-ddTHH:mm:ss.fffK";
    }


    // Ensure that all dates go out over the wire in full LOCAL time format (unless date has been specifically set to DateTimeKind.Utc)
    public override void WriteJson(JsonWriter writer,object value,JsonSerializer serializer)
    {
        if (value is DateTime)
        {
            // if datetime kind is unspecified then treat is as local time
            DateTime dateTime = (DateTime)value;
            if (dateTime.Kind == DateTimeKind.Unspecified)
            {
                dateTime = DateTime.SpecifyKind(dateTime,DateTimeKind.Local);
            }

            base.WriteJson(writer,dateTime,serializer);
        }
        else
        {
            base.WriteJson(writer,value,serializer);
        }
    }


    // Ensure that all dates arriving over the wire get parsed into LOCAL time
    public override object ReadJson(JsonReader reader,Type objectType,object existingValue,JsonSerializer serializer)
    {
        var result = base.ReadJson(reader,objectType,existingValue,serializer);

        if (result is DateTime)
        {
            DateTime dateTime = (DateTime)result;
            if (dateTime.Kind != DateTimeKind.Local)
            {
                result = dateTime.ToLocalTime();
            }
        }

        return result;
    }
}

最后,我们创建了一个CustomBreezeConfig类：

public class CustomBreezeConfig : Breeze.WebApi.BreezeConfig
{

    protected override JsonSerializerSettings CreateJsonSerializerSettings()
    {
        var baseSettings = base.CreateJsonSerializerSettings();

        // swap out the standard IsoDateTimeConverter that breeze installed with our own
        var timeConverter = baseSettings.Converters.OfType<IsoDateTimeConverter>().SingleOrDefault();
        if (timeConverter != null)
        {
            baseSettings.Converters.Remove(timeConverter);
        }
        baseSettings.Converters.Add(new JsonLocalDateTimeConverter());

        return baseSettings;
    }
}

就是这样欢迎所有意见和建议.