Linq: random order

Question

How can I change the code below to get 50 different random data from the database each time?

return (from examQ in idb.Exam_Question_Int_Tbl where examQ.Exam_Tbl_ID==exam_id select examQ).OrderBy(x=>x.Exam_Tbl_ID).Take(50); 

Answer 1

http://msdn.microsoft.com/en-us/library/system.guid.newguid.aspx

 return (from examQ in idb.Exam_Question_Int_Tbl where examQ.Exam_Tbl_ID==exam_id select examQ).OrderBy(x => Guid.NewGuid()).Take(50); 

If it's LINQ-to-SQL, you can simply add ORDER BY NEWID() to the SELECT statement.

As already noted, it might be better to use an algorithm like Fisher-Yates Shuffle , here is the implementation: https://stackoverflow.com/a/212718/

Answer 2

How big is the collection? Can you select them all in memory and then select a random collection? If so, then Shuffle's algorithm. Is using Random and OrderBy a good shuffle algorithm? - a good choice.

 return idb.Exam_Question_Int_Tbl .Where( e => e.Exam_Tbl_ID == exam_id ) .ToList() .Shuffle() .Take( 50 ); 

If not, then I would suggest a stored procedure that does newid() ordering newid() SQL Server Random Sort ). I don't think there is any way to translate an expression based on a random number generator in C # in LINQ to SQL / Entities.

Answer 3

If you have the same problem, I had ...

 int Limit = 24; return (from Q in Context.table where Q.some_key == 1234 select new classDataType() { FirstAttribute = Q.FirstCol, SecondAttribute = Q.SecondCol, ThirdAttribute = Q.ThirdCol }).ToList().OrderBy(x => Guid.NewGuid()).Take(Limit).ToList(); 

After sql-linq, it should be a LIST, so maybe you need to change the list before using the OrderBy-NewGuid method:

 return (...-SQL-SELECT-LINQ-...) .ToList() //**** .OrderBy(x => Guid.NewGuid()).Take(Limit).ToList();