C# 匿名类型 foreach 循环，更好的方法

本文关键字：更好 方法 循环 foreach 类型 | 更新日期: 2023-09-27 17:56:08

我有一个简单的匿名类型的foreach循环，我想知道是否有办法使其更有效率。

如果它循环浏览 155 个项目，则需要大约 20 秒才能完成。我省略了它在boAsset对象上设置的其他一些属性，但没有什么特别的 - 只是Strings/Integers。

有什么想法吗？

List<BoAsset> assetList = new List<BoAsset>();
foreach (var asset in result)
{
     BoAsset boAsset = new BoAsset();
     boAsset.Description = asset.Description;
     boAsset.DetailedDescription = asset.DetailedDescription;
     boAsset.AssetCustomerID = asset.AssetCustomerID;
     boAsset.AssetId = asset.AssetId;
     boAsset.Keywords = asset.Keywords;
     boAsset.Notes = asset.Notes;
     boAsset.Photographer = asset.Photographer;
     boAsset.PhotographerEmail = asset.PhotographerEmail;
     boAsset.Notes = asset.Notes;
     boAsset.Author = asset.Author;
     boAsset.FileName = asset.FileName;
     boAsset.FileExtension = asset.FileExtension;
     boAsset.AssetCreateDate = asset.AssetCreateDate;
     boAsset.AssetExpireDate = asset.AssetExpireDate;
     assetList.Add(boAsset);
}

var query =   (from a in context.Assets
              join subAf1 in context.AssetFiles on new { aid = a.AssetID, ftid = 1 } equals new { aid = subAf1.AssetID, ftid = subAf1.AssetTypeID } into theAf1
              from Af1 in theAf1.DefaultIfEmpty()
              join subAf2 in context.AssetFiles on new { aid = a.AssetID, ftid = 2 } equals new { aid = subAf2.AssetID, ftid = subAf2.AssetTypeID } into theAf2
              from Af2 in theAf2.DefaultIfEmpty()
              join subAf3 in context.AssetFiles on new { aid = a.AssetID, ftid = 3 } equals new { aid = subAf3.AssetID, ftid = subAf3.AssetTypeID } into theAf3
              from Af3 in theAf3.DefaultIfEmpty()
              join subAf4 in context.AssetFiles on new { aid = a.AssetID, ftid = 4 } equals new { aid = subAf4.AssetID, ftid = subAf4.AssetTypeID } into theAf4
              from Af4 in theAf4.DefaultIfEmpty()
              join subAf5 in context.AssetFiles on new { aid = a.AssetID, ftid = 5 } equals new { aid = subAf5.AssetID, ftid = subAf5.AssetTypeID } into theAf5
              from Af5 in theAf5.DefaultIfEmpty()
              join subFp in context.FilePaths on new { fpid = Af1.FilePathID } equals new { fpid = subFp.FilePathID } into theFp1
              from fp1 in theFp1.DefaultIfEmpty()
              //join fp in context.FilePaths on Af1.FilePathID equals fp.FilePathID
              where a.AssetCustomerID == custId && a.AssetID == assetId
              select new { a, Af1, Af2, Af3, Af4, Af5, fp1 }).Distinct();
var result =   from q in query
               select new
               {
                   AssetId = q.a.AssetID,
                   AssetCustomerId = q.a.AssetCustomerID,
                   StockImage = q.a.StockImage,
                   Description = q.a.Description,
                   DetailedDescription = q.a.DetailedDescription,
                   Author = q.a.Author,
                   FileName = q.Af1.FileName, //was 1
                   FileExtension = q.Af1.FileExtension, //was 1
                   AssetCreateDate = q.a.AssetCreateDate,
                   AssetExpireDate = q.a.AssetExpireDate,
                   AssetActivateDate = q.a.AssetActivateDate,
                   Notes = q.a.Notes,
                   Keywords = q.a.Keywords,
                       Photographer = q.a.Photographer,
                       PhotographerEmail = q.a.PhotographerEmail
               }

C# 匿名类型 foreach 循环，更好的方法

创建 155 个对象并将数据复制到其中的时间大约是一毫秒。您无法对该代码执行任何操作来进行任何重大（甚至显着）改进。

如果要节省任何时间，则应查看创建结果的查询。这就是需要时间的。

我认为

您的查询太复杂了（连接太多），特别是考虑到有一些甚至没有使用。

请注意，如果查询很复杂，某些 LINQ 提供程序（如 LINQ to Entities）在简单地处理查询树以将其转换为 SQL 时可能需要相当长的时间。（我已经有一些查询需要 10 或 15 秒才能让 EF 对其进行分析。

如果，正如我怀疑的那样，您正在使用的 LINQ 实现正在访问数据库，请使用 SQL 分析工具来检查传递给服务器的实际 SQL 以及该 SQL 的性能如何。

另外，请注意，给定您使用的字段，您实际上可以通过将结果直接具体化到BoAsset对象中来取消foreach循环。

那是：

var result = from q in query
             select new BoAsset
             {
                 AssetId = q.a.AssetID,
                 AssetCustomerId = q.a.AssetCustomerID,
                 StockImage = q.a.StockImage,
                 Description = q.a.Description,
                 DetailedDescription = q.a.DetailedDescription,
                 Author = q.a.Author,
                 FileName = q.Af1.FileName, //was 1
                 FileExtension = q.Af1.FileExtension, //was 1
                 AssetCreateDate = q.a.AssetCreateDate,
                 AssetExpireDate = q.a.AssetExpireDate,
                 AssetActivateDate = q.a.AssetActivateDate,
                 Notes = q.a.Notes,
                 Keywords = q.a.Keywords,
                 Photographer = q.a.Photographer,
                 PhotographerEmail = q.a.PhotographerEmail
             };
List<BoAsset> assetList = result.ToList();
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