EF Code First: How to get random rows
How can I build a query where I would retrieve random rows?
If I were to write it in SQL then I would put an order by on newid() and chop off n number of rows from the top. Anyway to do this in EF code first?
I have tried creating a query that uses newid() and executing it using DbSet.SqlQuery(). while it works, its not the cleanest of solutions.
Also, tried retrieve all the rows and sorting them by a new guid. Although the number of rows are fairly small, its still not a good solution.
Any ideas?
Just call:
something.OrderBy(r => Guid.NewGuid()).Take(5)
Comparing two options:
Skip(random number of rows)
Method
private T getRandomEntity<T>(IGenericRepository<T> repo) where T : EntityWithPk<Guid> {
var skip = (int)(rand.NextDouble() * repo.Items.Count());
return repo.Items.OrderBy(o => o.ID).Skip(skip).Take(1).First();
}
- Takes 2 queries
Generated SQL
SELECT [GroupBy1].[A1] AS [C1]
FROM (SELECT COUNT(1) AS [A1]
FROM [dbo].[People] AS [Extent1]) AS [GroupBy1];
SELECT TOP (1) [Extent1].[ID] AS [ID],
[Extent1].[Name] AS [Name],
[Extent1].[Age] AS [Age],
[Extent1].[FavoriteColor] AS [FavoriteColor]
FROM (SELECT [Extent1].[ID] AS [ID],
[Extent1].[Name] AS [Name],
[Extent1].[Age] AS [Age],
[Extent1].[FavoriteColor] AS [FavoriteColor],
row_number() OVER (ORDER BY [Extent1].[ID] ASC) AS [row_number]
FROM [dbo].[People] AS [Extent1]) AS [Extent1]
WHERE [Extent1].[row_number] > 15
ORDER BY [Extent1].[ID] ASC;
Guid
Method
private T getRandomEntityInPlace<T>(IGenericRepository<T> repo) {
return repo.Items.OrderBy(o => Guid.NewGuid()).First();
}
Generated SQL
SELECT TOP (1) [Project1].[ID] AS [ID],
[Project1].[Name] AS [Name],
[Project1].[Age] AS [Age],
[Project1].[FavoriteColor] AS [FavoriteColor]
FROM (SELECT NEWID() AS [C1],
[Extent1].[ID] AS [ID],
[Extent1].[Name] AS [Name],
[Extent1].[Age] AS [Age],
[Extent1].[FavoriteColor] AS [FavoriteColor]
FROM [dbo].[People] AS [Extent1]) AS [Project1]
ORDER BY [Project1].[C1] ASC