外连接和 Linq

发布于 2024-07-10 21:01:47 字数 861 浏览 9 评论 0原文

所以我有以下代码：

  return from a in DBContext.Acts
         join artist in DBContext.Artists on a.ArtistID equals artist.ID into art
         from artist in art.DefaultIfEmpty()

         select new Shared.DO.Act
         {
             ID = a.ID,
             Name = a.Name,
             Artist = new Shared.DO.Artist
             {
                 ID = artist.ID,
                 Name = artist.Name
             },
             GigId = a.GigID
         };

这会加载一个 act 对象并将其从 linq 对象调整为我的域 act 对象。

正如您所看到的，我已经定义了艺术家与表演关系的外部连接。

我这样做是因为我一直想要这个表演，无论它是否有艺术家。

如果该表演确实有艺术家，那么效果非常好。

如果没有，那么代码就死了。这就是罪魁祸首：

 Artist = new Shared.DO.Artist
          {
              ID = artist.ID,
              Name = artist.Name
          },

如果我把它去掉，那就没问题了。可以做我正在尝试的事情吗？

原文

So I have the following code:

  return from a in DBContext.Acts
         join artist in DBContext.Artists on a.ArtistID equals artist.ID into art
         from artist in art.DefaultIfEmpty()

         select new Shared.DO.Act
         {
             ID = a.ID,
             Name = a.Name,
             Artist = new Shared.DO.Artist
             {
                 ID = artist.ID,
                 Name = artist.Name
             },
             GigId = a.GigID
         };

This loads an act object and adapts it from a linq object to my domain act object.

As you can see I have defined an outer join on the artist to act relationship.

I have done this because I always want the act, irrespective of if it has an artist.

This works really well if the act does indeed have an artist.

If it doesnt then the code dies. This is the the culprit:

 Artist = new Shared.DO.Artist
          {
              ID = artist.ID,
              Name = artist.Name
          },

If I remove it, its fine. Is it possible to do what I'm attempting?

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梦巷 2024-07-17 21:01:47

           Artist = new Shared.DO.Artist
           {
               ID = artist == null ? Guid.NewGuid() : artist.ID,
               Name = artist == null ? string.Empty : artist.Name
           }

或者，向 Shared.DO.Artist 添加一个构造函数，该构造函数采用 Artist 的 Linq 表示形式。构造函数可以检查 null 并执行所有初始化。

           Artist = new Shared.DO.Artist
           {
               ID = artist == null ? Guid.NewGuid() : artist.ID,
               Name = artist == null ? string.Empty : artist.Name
           }

Alternatively, add a constructor to Shared.DO.Artist that takes the Linq representation of Artist. The constructor can check for null and perform all initialization.

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就像说晚安 2024-07-17 21:01:47

实际上......这对我来说似乎是最好的答案......

Artist = artist == null ? null : new Shared.DO.Artist
                    {
                       ID =  artist.ID,
                       Name = artist.Name
                    },

Actually... this seems the best answer for me....

Artist = artist == null ? null : new Shared.DO.Artist
                    {
                       ID =  artist.ID,
                       Name = artist.Name
                    },

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