将日期时间转换为LINQ-to-entities查询中的格式化字符串 [英] Convert datetime to a formatted string inside a LINQ-to-entities query

问题描述

如何将DateTime转换为格式化的字符串?

How can I convert DateTime into a formatted string?

这是以下查询中需要帮助的行:

This is the line in the following query that needs help:

StartDate = string.Format("{0:dd.MM.yy}", p.StartDate)

整个查询:

var offer = (from p in dc.CustomerOffer
             join q in dc.OffersInBranch
             on p.ID equals q.OfferID
             where q.BranchID == singleLoc.LocationID
             let value = (p.OriginalPrice - p.NewPrice) * 100 / p.OriginalPrice
             orderby value descending
             select new Offer()
             {
                 Title = p.OfferTitle,
                 Description = p.Description,
                 BestOffer = value,
                 ID = p.ID,
                 LocationID = q.BranchID,
                 LocationName = q.CustomerBranch.BranchName,
                 OriginalPrice = SqlFunctions.StringConvert((decimal)p.OriginalPrice),
                 NewPrice = SqlFunctions.StringConvert((decimal)p.NewPrice),
                 StartDate = string.Format("{0:dd.MM.yy}", p.StartDate)
             }).First();

我收到以下错误消息:

LINQ to Entities无法识别方法'System.String ToString(System.String)'，并且该方法无法转换为商店表达式.

LINQ to Entities does not recognize the method 'System.String ToString(System.String)' method, and this method cannot be translated into a store expression.

推荐答案

现在，我明白了这个问题，现在再给它一个镜头:)

Now that I understand the question, I'm giving it another shot :)

var offer = (from p in dc.CustomerOffer
                     join q in dc.OffersInBranch
                         on p.ID equals q.OfferID
                     where q.BranchID == singleLoc.LocationID
                     let value = (p.OriginalPrice - p.NewPrice) * 100 / p.OriginalPrice
                     orderby value descending
                     select new
                     {
                         Title = p.OfferTitle,
                         Description = p.Description,
                         BestOffer=value,
                         ID=p.ID,
                         LocationID=q.BranchID,
                         LocationName=q.CustomerBranch.BranchName,
                         OriginalPrice=SqlFunctions.StringConvert((decimal)p.OriginalPrice),
                         NewPrice=SqlFunctions.StringConvert((decimal)p.NewPrice),
                         StartDate=p.StartDate

                     })
                     .ToList()
                     .Select(x => new Offer()
                     {
                         Title = x.OfferTitle,
                         Description = x.Description,
                         BestOffer=value,
                         ID=x.ID,
                         LocationID=x.BranchID,
                         LocationName=x.CustomerBranch.BranchName,
                         OriginalPrice=x.OriginalPrice,
                         NewPrice=x.NewPrice,
                         StartDate=x.StartDate.ToString("dd.MM.yy")
                     }).First();

我知道它有点长，但这就是Linq To SQL的问题.

I know it's a bit long, but that's the problem with Linq To SQL.

使用linq时，直到使用诸如ToList()或First()之类的会导致实际对象的东西时，数据库调用才会执行.一旦第一个.First()调用执行了该SQL调用，您现在就可以使用.NET类型，并且可以使用DateTime内容.

When you use linq, the database call isn't executed until you use something such as ToList() or First() that results in actual objects. Once that SQL call is executed by the first .First() call, you're now working with .NET types, and can use DateTime stuff.

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