在 LINQ 中使用强类型对象执行 JOIN

发布于 2024-11-02 14:11:20 字数 616 浏览 0 评论 0原文

我有两个使用实体数据模型生成的对象。这些对象如下所示：

public class Song
{
  public int ID { get; set; }
  public string Title { get; set; }
  public double Duration { get; set; }
}

public class AlbumSongLookup
{
  public int ID { get; set; }
  public int SongID { get; set; }
  public int AlbumID { get; set; }
}

我需要使用 LINQ 获取专辑的 Song 对象。我有专辑ID。目前，我正在尝试：

int albumID = GetAlbumID();
var results = from lookup in context.AlbumSongLookups
              where lookup.AlbumID=albumID
              select lookup;

我知道我需要加入。但我不确定的是，如何使用此 LINQ 查询将结果获取为 Song 对象？

谢谢！

原文

I have two objects that have been generated with an entity data model. The objects look like the following:

public class Song
{
  public int ID { get; set; }
  public string Title { get; set; }
  public double Duration { get; set; }
}

public class AlbumSongLookup
{
  public int ID { get; set; }
  public int SongID { get; set; }
  public int AlbumID { get; set; }
}

I need to get the Song objects for an Album using LINQ. I have the Album ID. Currently, I'm trying:

int albumID = GetAlbumID();
var results = from lookup in context.AlbumSongLookups
              where lookup.AlbumID=albumID
              select lookup;

I understand that I need to do a join. But what I'm not sure about is, how do I get the results to be Song objects with this LINQ query?

Thanks!

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离旧人 2024-11-09 14:11:20

此查询返回您期望的结果吗？

var results = from lookup in context.AlbumSongLookups
              join song in context.Songs on lookup.SongID equals song.ID
              where lookup.AlbumID == albumID
              select song;

我假设这里存在 context.Songs 。

Does this query return what you're expecting?

var results = from lookup in context.AlbumSongLookups
              join song in context.Songs on lookup.SongID equals song.ID
              where lookup.AlbumID == albumID
              select song;

I'm assuming the existence of context.Songs here.

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空心↖ 2024-11-09 14:11:20

这不行吗？

from lookup in context.AlbumSongLookups
from songs in context.Song
where lookup.SongID == songs.ID && lookup.SongID == albumID
select songs

does this not work?

from lookup in context.AlbumSongLookups
from songs in context.Song
where lookup.SongID == songs.ID && lookup.SongID == albumID
select songs

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从来不烧饼 2024-11-09 14:11:20

您可以将“导航属性”添加到“歌曲”实体，这样您就可以直接访问特定专辑的相应歌曲。实体框架将为您完成繁重的工作。

在您的情况下，它返回一个查找集合，您需要做的是查找与它们对应的 Song 对象。这可以使用以下方法完成：

int albumID = GetAlbumID();
var results = from lookup in context.AlbumSongLookups
              where lookup.AlbumID=albumID
              select context.Songs.SingleOrDefault(s=>s.SongID==lookup.SongID);

You could add a "Navigation Property" to your "Song" Entity, this way, you'll be able to directly access the corresponding Songs of a particular album. Entity framework will do the heavy lifting for you.

In your case, it returns a collection of lookups, what you need to do is look for the Song objects corresponding to them. this can be done using:

int albumID = GetAlbumID();
var results = from lookup in context.AlbumSongLookups
              where lookup.AlbumID=albumID
              select context.Songs.SingleOrDefault(s=>s.SongID==lookup.SongID);

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伴我老 2024-11-09 14:11:20

像这样的东西应该有效：

int albumID = GetAlbumID();
var songIDs = from lookup in contenxt.AlbumSongLookups
              where lookup.AlbumID == albumID
              select lookup.SongID;
var results = from song in context.Songs
              where song.SongID in SongIDs
              select song;

Something like this should work:

int albumID = GetAlbumID();
var songIDs = from lookup in contenxt.AlbumSongLookups
              where lookup.AlbumID == albumID
              select lookup.SongID;
var results = from song in context.Songs
              where song.SongID in SongIDs
              select song;

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