Question

I’ve been trying to write a linq query but the groupby performance is horrifically slow, so I wrote my query in SQL instead and it’s really speady but I can’t get linq pad to convert it to linq for me. Can any body help me convert this sql to Linq please:

(SELECT mm.rcount, * FROM
(SELECT m.TourID AS myId, COUNT(m.RecordType) AS rcount FROM
(
((SELECT *
FROM Bookings h
WHERE h.RecordType = 'H' AND h.TourArea like '%bull%')
union
(SELECT *
FROM Bookings t
WHERE t.RecordType = 'T' and t.TourGuideName like '%bull%'))
) m
group by m.TourID) mm
INNER JOIN Bookings b ON mm.myId= b.TourID
WHERE b.RecordType = 'H');

here’s my LINQ effort but it takes like 20 seconds to iterate over 200 records:

        var heads = from head in db.GetTable<BookingType>()
                    where head.RecordType == "H" &&
                    head.TourArea.Contains("bull")
                    select g;

        var tgs = from tourguides in db.GetTable<BookingType>()
                  where tourguides.RecordType == "T" &&
                  tourguides.TourGuideName.Contains("bull")
                  select tourguides;

        var all = heads.Union(tgs);
        var groupedshit = from r in all
                          group r by r.BookingID into g
                          select g;

        return heads;

Edit 1:
Here’s my database structure:

BookingID [PK] | TourID | RecordType | TourArea | TourGuideName | ALoadOfOtherFields

And here’s some sample data:

1 | 1 | H | Bullring | null

2 | 1 | T | null | Bulldog

3 | 2 | H | Bullring | null

4 | 2 | T | null | Bulldog

5 | 2 | T | null | bull stamp

There will only ever be a single H (head) record but could potentially have many T (tour guide) records. After the grouping if I select a new (like this question: How to use LINQ to SQL to create ranked search results?) on the .Contains(‘bull’) with a .Count() I can then get ranked searching (which is the whole point of this exercise).

Edit 2:
I’ve added in a property for search rank in the class itself to avoid the problem of then converting my results into a key/value pair. I don’t know if this is best practice but it works.

    /// <summary>
    /// Search Ranking
    /// </summary>
    public int? SearchRank { get; set; }

and then I execute a SQL query directly using linq-to-sql:

        IEnumerable<BookingType> results = db.ExecuteQuery<BookingType>
        ("(SELECT  mm.rcount AS SearchRank, b.* FROM (SELECT m.TourID AS myId, COUNT(m.RecordType) AS rcount FROM (((SELECT * FROM Bookings h WHERE h.RecordType = 'H' AND h.TourArea like '%{0}%') union (SELECT * FROM Bookings t WHERE t.RecordType = 'T' and t.TourGuideName like '%{0}%')) ) m group by m.TourID) mm INNER JOIN Bookings b ON mm.myId= b.TourID WHERE b.RecordType = 'H')", "bull");

I can add in as many ‘AND’s and ‘OR’s as I like now without Linq-to-sql going mental (the query it generated was a crazy 200 lines long!

Ranked Search viola!

Answer 1

Why bother converting it? You can just call the SQl you have opptimized.