I am new to Linq to Entity and here is my test scenario:
I want to write a method which displays Count and Name of Tags used in Albums of a particular User using Linq.
Here is the method that I wrote and it works fine
public static void TestStatistics(int userId)
{
// select AlbumTitle, TagName, TagCount where UserId = userId
var results = from photo in dbSet.PhotoSet
join album in dbSet.AlbumSet on photo.AlbumId equals album.Id into albumSet
from alb in albumSet
where alb.UserId == userId
join photoTag in dbSet.PhotoTagSet on photo.Id equals photoTag.PhotoId into photoTagSet
from pt in photoTagSet
join tag in dbSet.TagSet on pt.TagId equals tag.Id
group new { alb, tag } by new { alb.Title, tag.Name }
into resultSet
orderby resultSet.Key.Name
select new
{
AlbumTitle = resultSet.Key.Title,
TagName = resultSet.Key.Name,
TagCount = resultSet.Count()
};
foreach (var item in results)
{
Console.WriteLine(item.AlbumTitle + "\t" + item.TagName + "\t" + item.TagCount);
}
}
And this is the standart T-SQL query which does the same
SELECT a.Title AS AlbumTitle, t.Name AS TagName , COUNT(t.Name) AS TagCount
FROM TblPhoto p, TblAlbum a, TblTag t, TblPhotoTag pt
WHERE p.Id = pt.PhotoId AND t.Id = pt.TagId AND p.AlbumId = a.Id AND a.UserId = 1
GROUP BY a.Title, t.Name
ORDER BY t.Name
It is pretty obvious that standard T-SQL query is much simpler than the Linq query. I know Linq does not supposed to be simpler than T-SQL but this complexity difference makes me think that I am doing something terribly wrong. Besides the SQL query generated by Linq is extremly complex.
Is there any way to make the Linq query simpler?
I made it a little simpler without using joins but using a approach like used in T-SQL. Actually it is now as simple as T-SQL. Still no navigation properties and no relations on db.
var results = from photo in dbSet.PhotoSet
from album in dbSet.AlbumSet
from photoTag in dbSet.PhotoTagSet
from tag in dbSet.TagSet
where photo.AlbumId == album.Id && photo.Id == photoTag.PhotoId &&
tag.Id == photoTag.TagId && album.UserId == userId
group new { album, tag } by new { album.Title, tag.Name } into resultSet
orderby resultSet.Key.Name
select new {
AlbumTitle = resultSet.Key.Title,
TagName = resultSet.Key.Name,
TagCount = resultSet.Count()
};
If every photo has at least one tag , then try
var results = (from r in PhotoTag
where r.Photo.Album.UserID == userId
group r by new { r.Photo.Album.Title, r.Tag.Name } into resultsSet
orderby resultsSet.Key.Name
select new
{
AlbumTitle = resultsSet.Key.Title ,
TagName = resultsSet.Key.Name ,
TagCount = resultsSet.Count()
}
);
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