C# linq：随机排序
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linq: order by random
提问by user972087
How can I change below code, to each time get 50 different random data from database?
如何更改以下代码，每次从数据库中获取 50 个不同的随机数据？
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);
采纳答案by Tim Schmelter
http://msdn.microsoft.com/en-us/library/system.guid.newguid.aspx
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 this is LINQ-to-SQL you could simply add a ORDER BY NEWID()to your SELECT statement.
如果这是 LINQ-to-SQL，您可以简单地将 a 添加ORDER BY NEWID()到您的 SELECT 语句。
As commented it might be better to use an algorithm like Fisher-Yates Shuffle, here is an implementation: https://stackoverflow.com/a/375446/284240
正如评论的那样，使用像Fisher-Yates Shuffle这样的算法可能会更好，这是一个实现：https: //stackoverflow.com/a/375446/284240
回答by tvanfosson
How big is the collection? Can you select them all into memory then choose a random collection? If so, then the Shuffle algorithm at Is using Random and OrderBy a good shuffle algorithm?would be a good choice.
收藏量有多大？您可以将它们全部选择到内存中然后选择一个随机集合吗？如果是这样，那么使用 Random 和 OrderBy的 Shuffle 算法是一个好的 shuffle 算法吗？会是一个不错的选择。
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 an ordering by 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# to LINQ to SQL/Entities.
如果没有，那么我会建议一个按newid()（SQL Server Random Sort）排序的存储过程。我认为没有任何方法可以将基于 C# 中随机数生成器的表达式转换为 LINQ to SQL/Entities。
回答by Froschkoenig84
If you've the same problem, I had...
如果你有同样的问题，我有...
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 needs to be a LIST, so maybe U need changing to a list, before you're using the OrderBy-NewGuid-Method:
在 sql-linq 之后它需要是一个列表，所以在你使用 OrderBy-NewGuid-Method 之前，你可能需要更改为一个列表：
return (...-SQL-SELECT-LINQ-...)
.ToList() //****
.OrderBy(x => Guid.NewGuid()).Take(Limit).ToList();
